Noble metal-containing colloidal solution and method for producing the same, and exhaust gas-purifying catalyst using the same and method for producing the same

Abstract

To provide a noble metal-containing colloidal solution capable of forming an excellent exhaust gas cleaning catalyst exhibiting cleaning performance and oxygen supply performance at a low temperature.SOLUTION: A noble metal-containing colloid liquid comprising: a noble metal; Ce; Zr; and at least one rare-earth element other than Ce, wherein a 90% cumulative size (D90) in a volume-based particle size of a colloid particle is 20nm or less, and a content of the noble metal is 0.5 to 110 parts by mass with respect to 100 parts by mass of composite oxides of Ce, Zr, and the rare-earth element.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a precious metal-containing colloidal solution and a method for producing the same, as well as an exhaust gas purification catalyst using the same and a method for producing the same. [Background technology]

[0002] Exhaust gas purification catalysts have been used to remove harmful components such as hydrocarbons (HC) and nitrogen oxides (NOx) from exhaust gases from internal combustion engines such as automobile engines. Three-way catalysts, in which precious metals such as platinum, rhodium, and palladium are supported on a support made of alumina, titania, silica, zirconia, ceria, or the like, are widely known as such exhaust gas purification catalysts. Various precious metal support methods have been investigated for such three-way catalysts, from the viewpoints of improving the purification performance of unburned components at low temperatures and improving the oxygen supply performance of ceria or ceria-zirconia.

[0003] For example, JP 2022-530530 A (Patent Document 1) discloses a method for producing an automobile catalyst, in which a platinum group metal is dispersed in colloidal metal oxide nanoparticles having a D90 diameter of 1.0 nm to 50 nm to obtain a mixture, and the mixture is co-impregnated onto an alumina component, and ceria-zirconia nanoparticles are disclosed as the metal oxide nanoparticles.

[0004] Furthermore, Japanese Patent Laid-Open Publication No. 2010-12397 (Patent Document 2) discloses a method for producing an exhaust gas purification catalyst, which includes a step of adding a basic solution to an acidic solution containing Ce, Zr, and Pd to coprecipitate a first hydroxide containing Ce, Zr, and Pd, a step of adding a basic solution to an acidic solution containing Al to precipitate a second hydroxide containing Al, and a step of mixing the dispersion containing the first hydroxide and the dispersion containing the second hydroxide, and drying and calcining the resulting mixture.

[0005] Furthermore, Japanese Patent Application Laid-Open No. 2004-267961 (Patent Document 3) discloses that in a catalyst consisting of a catalytic metal (noble metal), a promoter metal such as a rare earth metal, and a carrier, the catalytic metal and the promoter metal are supported by attaching a multi-component metal colloid solution to the carrier, and that the multi-component metal colloid solution consists of metal cluster particles consisting of the catalytic metal, a protective agent such as polyethyleneimine that protects the metal cluster particles, and rare earth metal ions that bind to the protective agent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2022-530530 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-12397 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-267961 Summary of the Invention [Problem to be solved by the invention]

[0007] The exhaust gas purification catalysts described in Patent Documents 1 to 3 have problems such as insufficient heat resistance and burial of precious metal active sites, and therefore do not provide sufficient purification performance in the low temperature range immediately after starting an internal combustion engine such as an automobile engine, and their oxygen supply performance is also insufficient.

[0008] The present invention has been made in view of the problems associated with the above-mentioned conventional techniques, and aims to provide an exhaust gas purification catalyst that exhibits excellent purification performance and oxygen supply performance at low temperatures, a precious metal-containing colloidal solution for forming such an exhaust gas purification catalyst, and methods for producing them. [Means for solving the problem]

[0009] As a result of intensive research conducted by the present inventors to achieve the above object, it was found that a raw salt aqueous solution containing a Ce salt, a Zr salt, and a salt of a rare earth element X other than Ce and a neutralizing aqueous solution containing a dispersant were mixed at a shear rate of 100 sec -1 The present inventors have found that by mixing the above ingredients and neutralizing the raw salt aqueous solution, a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and the rare earth element X (CZX composite oxide) is prepared, and by adding a precious metal salt to the composite precursor nanocolloidal solution, a precious metal-containing colloidal solution containing a precious metal and composite precursor nanocolloid particles is obtained. The present inventors have also found that by using this precious metal-containing colloidal solution to support a CZX composite oxide and a precious metal on a carrier, an exhaust gas purification catalyst that exhibits excellent purification performance and oxygen supply performance at low temperatures even after exposure to high temperatures can be obtained, and have completed the present invention.

[0010] That is, the present invention provides the following aspects. [1] A composition containing a precious metal, Ce, Zr, and at least one rare earth element other than Ce, The cumulative 90% diameter (D90) in the volume-based particle size distribution of the colloidal particles is 20 nm or less, The noble metal-containing colloidal solution has a content of the noble metal of 0.5 to 110 parts by mass relative to 100 parts by mass of the composite oxide of Ce, Zr, and the rare earth element. [2] The noble metal-containing colloidal solution according to [1], wherein the cumulative 50% diameter (D50) in the volume-based particle size distribution of the colloidal particles is 1 to 15 nm. [3] The precious metal-containing colloidal solution according to [1] or [2], further containing at least one dispersant selected from the group consisting of monoethanolamine, diethanolamine, ethylenediamine, glycine, hexaaminocaproic acid, polyethyleneimine, cetyltrimethylammonium bromide, polyvinylpyrrolidone, ammonium polyacrylate, and ammonium salt-based carboxylic acid copolymer. [4] preparing a raw salt aqueous solution containing a Ce salt, a Zr salt, and a salt of at least one rare earth element other than Ce; preparing an aqueous neutralization solution containing a dispersant; The raw salt aqueous solution and the neutralization aqueous solution were mixed at a shear rate of 100 sec -1 a step of mixing the above and neutralizing the raw salt aqueous solution to prepare a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and the rare earth element; adding a noble metal salt to the composite precursor nanocolloidal solution to prepare a noble metal-containing colloidal solution containing the noble metal and the composite precursor nanocolloidal particles; A method for producing a precious metal-containing colloidal solution, comprising: [5] The method for producing a precious metal-containing colloidal solution according to [4], wherein the raw salt aqueous solution further contains a dispersant. [6] The method for producing a precious metal-containing colloidal solution according to [4] or [5], wherein the dispersant is at least one selected from the group consisting of monoethanolamine, diethanolamine, ethylenediamine, glycine, hexaaminocaproic acid, polyethyleneimine, cetyltrimethylammonium bromide, polyvinylpyrrolidone, ammonium polyacrylate, and ammonium salt-based carboxylic acid copolymer. [7] A catalyst for purifying exhaust gas, comprising the precious metal-containing colloidal solution according to any one of [1] to [3], and a composite oxide of Ce, Zr, and the rare earth element, and the precious metal, supported on a carrier. [8] A method for producing a catalyst for purifying exhaust gases, comprising attaching the noble metal-containing colloidal solution according to any one of [1] to [3] to a carrier, and then calcining the carrier.

[0011] Although the reason why the use of the noble metal-containing colloidal solution of the present invention enables the production of an exhaust gas purification catalyst that exhibits excellent purification and oxygen supply performance at low temperatures even after exposure to high temperatures is not entirely clear, the inventors speculate as follows. Specifically, it is speculated that in the noble metal-containing colloidal solution of the present invention, the noble metal is coordinated to the surface of composite precursor nanocolloidal particles composed of a precursor of a composite oxide of Ce, Zr, and at least one rare earth element X other than Ce (CZX composite oxide). It is speculated that by using such a noble metal-containing colloidal solution to support a noble metal on various supports, an exhaust gas purification catalyst can be obtained in which the noble metal, acting as an active site, is located on the surface of nanoscale, i.e., high-surface-area, CZX composite oxide particles. Furthermore, it is speculated that such an exhaust gas purification catalyst exhibits excellent purification and oxygen supply performance even at low temperatures, even when the active sites (noble metal) are poisoned by hydrocarbons, because oxygen is readily supplied from the CZX composite oxide particles, accelerating the oxidation of hydrocarbons on the active sites (noble metal). Furthermore, in the exhaust gas purification catalyst, since the composite oxide contains rare earth elements other than Ce in addition to Ce and Zr, it is presumed that the catalyst has excellent heat resistance and will exhibit excellent purification performance and oxygen supply performance even after being exposed to high temperatures. [Effects of the Invention]

[0012] According to the present invention, it is possible to obtain an exhaust gas purification catalyst that has excellent purification performance and oxygen supply performance at low temperatures even after exposure to high temperatures, and a precious metal-containing colloidal solution for forming such an exhaust gas purification catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below based on preferred embodiments thereof.

[0014] [Noble metal-containing colloidal solution] First, the noble metal-containing colloidal solution of the present invention will be described. The noble metal-containing colloidal solution of the present invention contains a noble metal, Ce, Zr, and at least one rare earth element other than Ce, and the 90% cumulative diameter (D90) in the volume-based particle size distribution of the colloidal particles is 20 nm or less, and the content of the noble metal is 0.5 to 110 parts by mass per 100 parts by mass of a composite oxide of Ce, Zr, and the rare earth element.

[0015] Examples of the noble metal include Pd, Pt, Rh, and Ru. These noble metals may be used alone or in combination of two or more. Examples of rare earth elements X other than Ce include Sc, Y, La, Pr, and Nd. These rare earth elements X may be used alone or in combination of two or more.

[0016] In the noble metal-containing colloidal solution, the cumulative 90% diameter (D90) in the volume-based particle size distribution of the colloidal particles is 20 nm or less, preferably 15 nm or less, more preferably 13 nm or less, and particularly preferably 11 nm or less. When D90 is equal to or less than the upper limit, a composite oxide (CZX composite oxide) containing nanoscale Ce and Zr and the rare earth element X, with the noble metal disposed on the surface, can be supported on the support, making it possible to obtain an exhaust gas purification catalyst that has excellent purification performance and oxygen supply performance at low temperatures even after exposure to high temperatures. There is no particular lower limit for D90, but it is preferably 3 nm or more.

[0017] Furthermore, in the noble metal-containing colloidal solution, the cumulative 50% diameter (D50) in the volume-based particle size distribution of the colloidal particles is preferably 1 to 15 nm, more preferably 1.5 to 10 nm, even more preferably 1.8 to 9 nm, and particularly preferably 2.0 to 7.5 nm. When D50 is within this range, a nanoscale CZX composite oxide having a noble metal disposed on its surface can be supported on a support, making it possible to obtain an exhaust gas purification catalyst that has excellent purification performance and oxygen supply performance at low temperatures even after exposure to high temperatures.

[0018] Furthermore, in the noble metal-containing colloidal solution, the content of the noble metal is 0.5 to 110 parts by mass, preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass, and even more preferably 3 to 30 parts by mass, relative to 100 parts by mass of the CZX composite oxide. When the content of the noble metal is within the above range, it is possible to obtain an exhaust gas purification catalyst that has excellent purification performance and oxygen supply performance at low temperatures even after exposure to high temperatures.

[0019] In the noble metal-containing colloidal solution, the Ce content in the CZX composite oxide is preferably 20 to 60 mol %, more preferably 30 to 55 mol %, and even more preferably 40 to 50 mol %, based on the total amount of cationic elements in the CZX composite oxide. When the Ce content is within the above range, the oxygen supply performance tends to be excellent.

[0020] Furthermore, in the noble metal-containing colloidal solution, the content of the rare earth element X in the CZX composite oxide is preferably 0.1 to 5 mol %, more preferably 0.5 to 4 mol %, and even more preferably 1 to 3 mol %, relative to the total amount of cationic elements in the CZX composite oxide. When the content of the rare earth element X is within the above range, the heat resistance tends to be excellent.

[0021] The noble metal-containing colloidal solution preferably contains a dispersant. Examples of such dispersants include monoethanolamine, diethanolamine, ethylenediamine, glycine, hexaaminocaproic acid, polyethyleneimine, cetyltrimethylammonium bromide, polyvinylpyrrolidone, ammonium polyacrylate (molecular weight: 200 to 30,000), and ammonium salt-based carboxylic acid copolymer (molecular weight: 200 to 30,000). These dispersants may be used alone or in combination. The inclusion of such a dispersant allows for the preparation of noble metal-containing colloidal particles in which the colloidal particles are uniformly dispersed, thereby enabling the preparation of an exhaust gas purification catalyst supported on a nanoscale CZX composite oxide having a noble metal disposed on its surface. Such a dispersant may also serve as a neutralizer in the neutralization aqueous solution used in the method for producing a noble metal-containing colloidal solution described below.

[0022] The noble metal-containing colloidal solution of the present invention can be produced, for example, by the following method.

[0023] [Method for producing a precious metal-containing colloidal solution] Next, a method for producing a noble metal-containing colloidal solution of the present invention will be described. preparing a raw salt aqueous solution containing a Ce salt, a Zr salt, and a salt of at least one rare earth element other than Ce; preparing an aqueous neutralization solution containing a dispersant; The raw salt aqueous solution and the neutralization aqueous solution were mixed at a shear rate of 100 sec -1 a step of mixing the above and neutralizing the raw salt aqueous solution to prepare a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and the rare earth element X; adding a noble metal salt to the composite precursor nanocolloidal solution to prepare a noble metal-containing colloidal solution containing the noble metal and the composite precursor nanocolloidal particles; The method includes:

[0024] (Preparation of raw salt aqueous solution) In the method for producing a precious metal-containing colloidal solution of the present invention, first, a raw salt aqueous solution containing a Ce salt, a Zr salt, and a salt of at least one rare earth element X other than Ce is prepared. The Ce salt, Zr salt, and salt of the rare earth element X are not particularly limited as long as they are salts containing Ce, Zeta, and the rare earth element X, respectively, and examples thereof include nitrates, sulfates, carbonates, acetates, oxalates, and phosphates. In the method for producing a precious metal-containing colloidal solution of the present invention, the Ce salt, Zr salt, and salt of the rare earth element X are dissolved in water so that the Ce, Zr, and rare earth element X salt are present in a predetermined ratio to prepare the raw salt aqueous solution. Furthermore, it is preferable to add the dispersant to the raw salt aqueous solution from the viewpoint of suppressing aggregation of the composite precursor nanocolloidal particles after neutralization.

[0025] (Preparation of neutralization aqueous solution) Next, a neutralization aqueous solution containing a dispersant and a neutralizing agent is prepared. In such a neutralization aqueous solution, the dispersant and the neutralizing agent may be different compounds, or one or more compounds may serve as both a dispersant and a neutralizing agent. Examples of dispersants include the compounds described above, and particularly effective neutralizing agents include monoethanolamine, diethanolamine, and ethylenediamine. In the method for producing a precious metal-containing colloidal solution of the present invention, the neutralization aqueous solution is prepared by dissolving such a dispersant and a neutralizing agent in water.

[0026] Furthermore, it is preferable to previously adjust the pH of the neutralization aqueous solution to a high level so that when the raw salt aqueous solution and the neutralization aqueous solution are mixed, the resulting mixed aqueous solution has a pH of preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. If the pH of the mixed aqueous solution is below the lower limit, the rare earth element X tends to become non-uniform.

[0027] (Preparation of nanocolloidal solution of CZX composite oxide precursor) The raw salt aqueous solution and the neutralization aqueous solution were mixed at a shear rate of 100 sec -1The raw salt aqueous solution is mixed at the above temperature. This neutralizes the raw salt aqueous solution, and a composite precursor nanocolloidal solution containing the precursor of the CZX composite oxide is obtained. If the raw salt aqueous solution and the neutralization aqueous solution are mixed at a shear rate below the lower limit, the particle size of the composite precursor nanocolloidal particles consisting of the precursor of the CZX composite oxide tends to increase. In addition, the shear rate is set to 100 sec -1 More than 3000sec is preferable. -1 The above is more preferable. An example of a method for mixing the raw material salt aqueous solution and the neutralization aqueous solution at such a shear rate is a method using an "apparatus for producing ultrafine particles and porous body precursors" (super agitation (SA) reactor) described in JP 2017-140611 A.

[0028] (Preparation of precious metal-containing colloidal solution) Next, a noble metal salt was added to the composite precursor nanocolloid solution obtained in this way so that the ratio of the noble metal to the CZX composite oxide was set to a predetermined ratio, and the mixture was stirred at a shear rate of 100 sec -1 The following are mixed to obtain a noble metal-containing colloidal solution: Examples of the noble metal salt include tetraammine hydroxide, tetraammine chloride, nitrate, and sulfate.

[0029] [Exhaust gas purification catalyst] Next, the exhaust gas purifying catalyst of the present invention will be described. The exhaust gas purifying catalyst of the present invention is obtained using the noble metal-containing colloidal solution of the present invention, and has the CZX composite oxide and the noble metal supported on a carrier.

[0030] Examples of the carrier include oxides such as alumina, titania, silica, zirconia, and ceria. The carrier may also be a composite oxide containing an additive element in these oxide carriers to improve heat resistance or functionality, such as ceria-zirconia, which exhibits oxygen supply performance, ceria-zirconia with an additive element dissolved therein, or a diffusion barrier composite oxide containing alumina or the like that is not dissolved therein. The carrier may be used alone or in combination of two or more.

[0031] In the exhaust gas purification catalyst, the content of the noble metal is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, and even more preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of the support. When the content of the noble metal is within the above range, it is possible to obtain an exhaust gas purification catalyst in which grain growth of the noble metal is suppressed after exposure to high temperatures.

[0032] In the exhaust gas purification catalyst, the content of the CZX composite oxide is preferably 1 to 100 parts by mass, more preferably 1.5 to 50 parts by mass, and even more preferably 3 to 20 parts by mass, per 100 parts by mass of the support. When the content of the noble metal is within the above range, pore clogging of the support is suppressed, and high dispersion can be maintained even after exposure to high temperatures.

[0033] The exhaust gas purifying catalyst of the present invention can be produced, for example, by the following method.

[0034] [Method for producing exhaust gas purification catalyst] Next, a method for producing the exhaust gas purifying catalyst of the present invention will be described. The method for producing the exhaust gas purifying catalyst of the present invention is a method in which the noble metal-containing colloidal solution of the present invention is attached to a support, followed by calcination. This results in an exhaust gas purifying catalyst in which the CZX composite oxide and the noble metal are supported on the support.

[0035] In the method for producing an exhaust gas purifying catalyst of the present invention, first, an aqueous dispersion of the carrier is prepared. Preferably, ammonia, monoethanolamine, diethanolamine, ethylenediamine, or the like is added to the aqueous dispersion of the carrier so that the pH of the aqueous dispersion of the carrier is close to that of the precious metal-containing colloidal solution.

[0036] Next, the precious metal-containing colloidal solution of the present invention, prepared to have the desired amounts of precious metal and CZX composite oxide, is added to the aqueous dispersion of the carrier whose pH has been adjusted, and the resulting suspension is evaporated to dryness and calcined to decompose and remove the by-product salt. This results in an exhaust gas purification catalyst in which the CZX composite oxide and the precious metal are supported on the carrier, and preferably in which nanoscale CZX composite oxide particles are supported on the carrier and the precious metal is disposed on the surface of the supported particles. [Example]

[0037] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0038] Example 1 (Preparation of raw salt aqueous solution) A raw salt solution A-1 containing Ce, Zr, and La (Ce:Zr:La = 47.5:50:2.5 (molar ratio)) was prepared by dissolving 23.44 g of diammonium cerium nitrate (Ce(NH)(NO)), 12.03 g of zirconium oxynitrate dihydrate (ZrO(NO) 2H0), and 0.9743 g of lanthanum nitrate hexahydrate (La(NO) 6H0) in ion-exchanged water to a volume of 100 ml. 20 g of glycine (HNCHCOOH) was added and the solution was stirred using a magnetic stirrer. Ion-exchanged water was then added to bring the total volume to 130 ml.

[0039] (Preparation of neutralization aqueous solution) Ion-exchanged water was added to 20 g of ammonium polyacrylate (50 g of a water-soluble acrylic acid-based dispersant containing 40% by mass of ammonium polyacrylate with a molecular weight of 6000 ("Aron A-30SL" manufactured by Toa Gosei Co., Ltd.) was used), and the solution was dispersed to a volume of 100 ml. 15 g of glycine was then dissolved therein, and monoethanolamine (HN(CH)OH) was added so that the pH would be approximately 9 when the raw salt aqueous solution A-1 and the resulting neutralization aqueous solution B-1 were mixed at a volume ratio of 1:1. Ion-exchanged water was then added to a total volume of 130 ml, thereby preparing a neutralization aqueous solution B-1 containing a dispersant and a neutralizing agent.

[0040] (Preparation of start-up solution) 5 g of glycine was dissolved in 40 ml of ion-exchanged water, and monoethanolamine was added to adjust the pH to 9 to prepare a start-up solution.

[0041] (Preparation of Composite Precursor Nanocolloidal Solution) Using the "Apparatus for Producing Ultrafine Particles and Porous Material Precursors" (Super Agitation (SA) Reactor) described in JP 2017-140611 A, the raw salt aqueous solution A-1 and the neutralization aqueous solution B-1 were mixed to prepare a composite precursor nanocolloid solution. Specifically, the start-up solution was placed in the reaction vessel 20 shown in Figure 1 of the aforementioned patent publication, and an outer nozzle-type homogenizer 10 was installed. The shear rate was approximately 4900 sec -1 The raw salt aqueous solution A-1 and the neutralization aqueous solution B-1 were supplied and mixed under conditions of a rotor rotation speed of 3600 rpm and a liquid feed rate of 5 ml / min, and the raw salt aqueous solution A-1 was neutralized to prepare a CZL precursor nanocolloidal solution, which was a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and La (CZL composite oxide) with a cation concentration of 0.3 mol / L.

[0042] (Preparation of precious metal-containing colloidal solution) A predetermined amount of tetraamminepalladium hydroxide (Pd(NH3)4(OH)2) was added to the CZL precursor nanocolloidal solution so that the Pd:CZL ratio was 1.0:10 (mass ratio, CZL was calculated as oxide), and the mixture was stirred at 250 rpm for 30 minutes using a magnetic stirrer. After that, the mixture was left to stand overnight to prepare a Pd(1)CZL(10) colloidal solution, which is a precious metal-containing colloidal solution containing Pd as the precious metal.

[0043] (Catalyst Preparation) Al2O3 powder (AKP-G015, manufactured by Sumitomo Chemical Co., Ltd.) was dispersed in ion-exchanged water, and monoethanolamine was added to adjust the pH to 9 to prepare an Al2O3 aqueous dispersion. A predetermined amount of the Pd(1)CZL(10) colloidal solution was added to this Al2O3 aqueous dispersion to achieve a Pd:CZL:Al2O3 = 1.0:10:100 (mass ratio, CZL is oxide equivalent), and the resulting suspension was evaporated to dryness. The resulting powder was calcined in air at 300 °C for 6 hours to prepare a Pd(1)CZL(10)-supported Al2O3(100) catalyst powder.

[0044] Example 2 A Pd(2)CZL(10) colloidal solution, which is a precious metal-containing colloidal solution, was prepared in the same manner as in Example 1, except that the amount of tetraamminepalladium hydroxide (Pd(NH3)4(OH)2) added was changed so that the Pd:CZL ratio was 2.0:10 (mass ratio). Furthermore, a Pd(2)CZL(10)-supported Al2O3(100) catalyst powder was prepared.

[0045] Example 3 A Pd(10)CZL(10) colloidal solution, which is a precious metal-containing colloidal solution, was prepared in the same manner as in Example 1, except that the amount of tetraamminepalladium hydroxide (Pd(NH3)4(OH)2) added was changed so that the Pd:CZL ratio was 10:10 (mass ratio). Furthermore, a Pd(10)CZL(10)-supported Al2O3(100) catalyst powder was prepared.

[0046] Example 4 A Pd(2)CZL(20)-supported Al2O3(100) catalyst powder was prepared in the same manner as in Example 1, except that twice the amount of the Pd(1)CZL(10) colloidal solution was added to achieve a Pd:CZL:Al2O3 = 2.0:20:100 (mass ratio).

[0047] Example 5 A Pd(5)CZL(50)-supported Al2O3(100) catalyst powder was prepared in the same manner as in Example 1, except that five times the amount of the Pd(1)CZL(10) colloidal solution was added to achieve a Pd:CZL:Al2O3 = 5.0:50:100 (mass ratio).

[0048] Example 6 (Preparation of raw salt aqueous solution) A raw salt aqueous solution A-2 containing Ce, Zr, and La (Ce:Zr:La = 47.5:50:2.5 (molar ratio)) was prepared in the same manner as in Example 1, except that the amount of diammonium cerium nitrate (Ce(NH)(NO)) was changed to 15.62 g, the amount of zirconium oxynitrate dihydrate (ZrO(NO) 2H0) to 8.02 g, and the amount of lanthanum nitrate hexahydrate (La(NO) 6H0) to 0.6495 g.

[0049] (Preparation of neutralization aqueous solution) Ion-exchanged water was added to 20 g of the ammonium polyacrylate to disperse it to a liquid volume of 100 ml, and then 15 g of glycine was dissolved therein. Furthermore, monoethanolamine was added so that the pH would be about 9 when the raw salt aqueous solution A-2 and the resulting neutralization aqueous solution B-2 were mixed at a volume ratio of 1:1. Then, ion-exchanged water was added to make the total volume 130 ml, thereby preparing a neutralization aqueous solution B-2 containing a dispersant and a neutralizing agent.

[0050] (Preparation of composite precursor nanocolloidal solution and precious metal-containing colloidal solution) A CZL precursor nanocolloidal solution, which is a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and La (CZL composite oxide) with a cation concentration of 0.2 mol / L, was prepared in the same manner as in Example 1, except that the raw salt aqueous solution A-2 was used instead of the raw salt aqueous solution A-1 and the neutralization aqueous solution B-2 was used instead of the neutralization aqueous solution B-1.Furthermore, a Pd(1)CZL(10) colloidal solution, which is a noble metal-containing colloidal solution, was prepared.

[0051] (Catalyst Preparation) A Pd(1)CZL(10)-supported Al2O3(100) catalyst powder was prepared in the same manner as in Example 1, except that a Pd(1)CZL(10) colloidal solution with a cation concentration of 0.2 mol / L was added.

[0052] Example 7 A Pd(2)CZL(10) colloidal solution containing a precious metal was prepared in the same manner as in Example 6, except that the amount of tetraamminepalladium hydroxide (Pd(NH3)4(OH)2) added was changed so that the mass ratio of Pd:CZL was 2.0:10.

[0053] Example 8 A Pd(1)CZL(10) colloidal solution, which is a noble metal-containing colloidal solution, was prepared in the same manner as in Example 6, except that palladium nitrate (Pd(NO3)2) was added instead of tetraamminepalladium hydroxide.

[0054] Example 9 A Pd(1)CZL(10) colloidal solution, which is a noble metal-containing colloidal solution, was prepared in the same manner as in Example 1, except that palladium nitrate (Pd(NO3)2) was added instead of tetraamminepalladium hydroxide.

[0055] Example 10 (Preparation of raw salt aqueous solution) A raw salt solution A-3 containing Ce, Zr, and Y (Ce:Zr:Y = 47.5:50:2.5 (molar ratio)) was prepared in the same manner as in Example 6, except that 0.5745 g of yttrium nitrate hexahydrate (Y(NO) 6H0) was used instead of lanthanum nitrate hexahydrate.

[0056] (Preparation of neutralization aqueous solution) Ion-exchanged water was added to 20 g of the ammonium polyacrylate to disperse it to a liquid volume of 100 ml, and then 15 g of glycine was dissolved therein. Furthermore, monoethanolamine was added so that the pH would be about 9 when the raw salt aqueous solution A-3 and the resulting neutralization aqueous solution B-3 were mixed at a volume ratio of 1:1. Then, ion-exchanged water was added to make the total volume 130 ml, thereby preparing a neutralization aqueous solution B-3 containing a dispersant and a neutralizing agent.

[0057] (Preparation of composite precursor nanocolloidal solution and precious metal-containing colloidal solution) A CZY precursor nanocolloidal solution, which is a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and Y (CZY composite oxide) with a cation concentration of 0.2 mol / L, was prepared in the same manner as in Example 1, except that the raw salt aqueous solution A-3 was used instead of the raw salt aqueous solution A-1, and the neutralization aqueous solution B-3 was used instead of the neutralization aqueous solution B-1.Furthermore, a Pd(1)CZY(10) colloidal solution, which is a noble metal-containing colloidal solution, was prepared.

[0058] Example 11 A Pd(2)CZY(10) colloidal solution, which is a precious metal-containing colloidal solution, was prepared in the same manner as in Example 10, except that the amount of tetraamminepalladium hydroxide (Pd(NH3)4(OH)2) added was changed so that the Pd:CZY = 2.0:10 (mass ratio).

[0059] Example 12 (Preparation of raw salt aqueous solution) A raw salt solution A-4 containing Ce, Zr, and Y (Ce:Zr:Y = 47.5:50:2.5 (molar ratio)) was prepared in the same manner as in Example 1, except that 0.8618 g of yttrium nitrate hexahydrate (Y(NO) 6H0) was used instead of lanthanum nitrate hexahydrate.

[0060] (Preparation of neutralization aqueous solution) Ion-exchanged water was added to 20 g of the ammonium polyacrylate to disperse it to a liquid volume of 100 ml, and then 15 g of glycine was dissolved therein. Furthermore, monoethanolamine was added so that the pH would be about 9 when the raw salt aqueous solution A-4 and the resulting neutralization aqueous solution B-4 were mixed at a volume ratio of 1:1. Then, ion-exchanged water was added to make the total volume 130 ml, thereby preparing a neutralization aqueous solution B-4 containing a dispersant and a neutralizing agent.

[0061] (Preparation of composite precursor nanocolloidal solution and precious metal-containing colloidal solution) A CZY precursor nanocolloidal solution, which is a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and Y (CZY composite oxide) with a cation concentration of 0.3 mol / L, was prepared in the same manner as in Example 1, except that the raw salt aqueous solution A-4 was used instead of the raw salt aqueous solution A-1, and the neutralization aqueous solution B-4 was used instead of the neutralization aqueous solution B-1.Furthermore, a Pd(1)CZY(10) colloidal solution, which is a noble metal-containing colloidal solution, was prepared.

[0062] Example 13 A Pd(2)CZY(10) colloidal solution containing a precious metal was prepared in the same manner as in Example 12, except that the amount of tetraamminepalladium hydroxide (Pd(NH3)4(OH)2) added was changed so that the mass ratio of Pd:CZY was 2.0:10.

[0063] Example 14 A Pd(1)CZY(10) colloidal solution, which is a noble metal-containing colloidal solution, was prepared in the same manner as in Example 10, except that palladium nitrate (Pd(NO3)2) was added instead of tetraamminepalladium hydroxide.

[0064] Example 15 A Pd(1)CZY(10) colloidal solution containing a noble metal was prepared in the same manner as in Example 12, except that palladium nitrate (Pd(NO3)2) was added instead of tetraamminepalladium hydroxide.

[0065] (Comparative Example 1) (Preparation of raw salt aqueous solution not containing rare earth element X) A raw salt aqueous solution a-1 containing Ce and Zr (Ce:Zr = 50:50 (molar ratio)) was prepared by dissolving 13.71 g of diammonium cerium nitrate (Ce(NH4)2(NO3)6) and 6.68 g of zirconium oxynitrate dihydrate (ZrO(NO3)2·2H2O) in ion-exchanged water, and then adding ion-exchanged water to bring the total volume to 200 ml.

[0066] (Preparation of neutralization aqueous solution) Ion-exchanged water was added to 2.61 g of polyethyleneimine (molecular weight: 10,000) to disperse it so that the liquid volume was 180 ml, and then ion-exchanged water was added to make the total volume 200 ml to prepare a neutralization aqueous solution b-1 containing a dispersant and a neutralizing agent.

[0067] (Preparation of Composite Precursor Nanocolloidal Solution) A CZ precursor nanocolloidal solution was prepared in the same manner as in Example 1, except that the raw salt aqueous solution a-1 was used instead of the raw salt aqueous solution A-1, the neutralization aqueous solution b-1 was used instead of the neutralization aqueous solution B-1, and 100 ml of ion-exchanged water was used as the start-up liquid, with a cation concentration of 0.1 mol / L, as a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce and Zr (CZ composite oxide) not containing the rare earth element X.

[0068] (Preparation of precious metal-containing colloidal solution) A Pd(1)CZ(10) colloidal solution, which is a precious metal-containing colloidal solution not containing the rare earth element X, was prepared in the same manner as in Example 1, except that the CZ precursor nanocolloidal solution was used instead of the CZL precursor nanocolloidal solution and palladium nitrate (Pd(NO3)2) was added instead of tetraamminepalladium hydroxide.

[0069] (Catalyst Preparation) An Al2O3 aqueous dispersion was prepared by dispersing Al2O3 powder in ion-exchanged water and adding nitric acid to adjust the pH to 2.3. A Pd(1)CZ(10)-supported Al2O3(100) catalyst powder containing no rare earth element X was prepared in the same manner as in Example 1, except that a predetermined amount of the Pd(1)CZ(10) colloidal solution was added to the Al2O3 aqueous dispersion.

[0070] (Comparative Example 2) (Preparation of Precious Metal-Containing Raw Salt Aqueous Dispersion and Alumina Precursor Aqueous Dispersion by Coprecipitation) A co-precipitated Pd(1)CZL(10) aqueous dispersion containing the precious metals was prepared by dissolving 2.0625 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O), 1.3363 g of zirconium oxynitrate dihydrate (ZrO(NO3)2·2H2O), and 0.1083 g of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) in ion-exchanged water to a volume of 100 ml, with the Ce:Zr:La molar ratio being 47.5:50:2.5 and the Pd:CZL mass ratio being 1.0:10 (CZL is calculated on an oxide basis). 0.3192 g of palladium nitrate (Pd(NO3)2) was then added, and the pH was adjusted to 10 with 25% aqueous ammonia.

[0071] In addition, 108.49 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) was dissolved in 250 ml of ion-exchanged water, and then 25% ammonia water was added to adjust the pH to 10 to prepare an aqueous dispersion of an alumina precursor containing Al hydroxide.

[0072] (Catalyst Preparation) The coprecipitated Pd(l)CZL(10) aqueous dispersion and the alumina precursor aqueous dispersion containing Al hydroxide were mixed and left overnight. After the supernatant was removed, the residue was collected by centrifugation and washed with water. The washed residue was dried at 150 °C for 10 hours and then calcined at 500 °C for 10 hours in air to prepare coprecipitated Pd(l)CZL(10)-supported Al2O3(100) catalyst powder.

[0073] (Comparative Example 3) (Preparation of a precious metal-containing raw salt water dispersion using a Pd colloidal solution) Palladium nitrate (Pd(NO3)2) (0.3192 g) and polyethyleneimine (PEI, molecular weight: 10,000) (0.5898 g) were dissolved in 20 ml of deionized water to prepare a Pd colloidal solution containing PEI as a protective agent. Next, cerium nitrate hexahydrate (Ce(NO3)3 6H2O) (2.0625 g), zirconium oxynitrate dihydrate (ZrO(NO3)2 2H2O) (1.3363 g), and lanthanum nitrate hexahydrate (La(NO3)3 6H2O) (0.1083 g) were dissolved in 100 ml of deionized water to prepare a raw salt solution a-2 containing Ce, Zr, and La (Ce:Zr:La = 47.5:50:2.5 (molar ratio)). The Pd colloidal solution was added to and mixed with this raw salt aqueous solution a-2 so that the Pd:CZL ratio was 1.0:10 (mass ratio, CZL is calculated as oxide), to prepare a precious metal-containing raw salt aqueous dispersion (Pd(1) colloid CZL(10) aqueous dispersion) containing Pd colloid, Ce, Zr, and La.

[0074] (Catalyst Preparation) 14.74 g of Al2O3 powder was added to the Pd(I) colloid CZL(10) aqueous dispersion, and while stirring at 3600 rpm using a homogenizer, 25% aqueous ammonia was added to neutralize the suspension until the pH reached 10. The resulting suspension was left to stand overnight, the supernatant was removed, and the residue was collected by centrifugation and washed with water. The washed residue was dried at 110 °C for 10 hours and then calcined at 400 °C in air for 1 hour to prepare a Pd(I) colloid CZL(10)-supported Al2O3(100) catalyst powder using Pd colloid and nitrate raw materials.

[0075] Comparative Example 4 A Pd(0.01)CZL(10) colloidal solution, which is a precious metal-containing colloidal solution, was prepared in the same manner as in Example 1, except that the amount of tetraamminepalladium hydroxide (Pd(NH3)4(OH)2) added was changed so that the Pd:CZL mass ratio was 0.01:10. Furthermore, a Pd(0.01)CZL(10)-supported Al2O3(100) catalyst powder was prepared.

[0076] (Comparative Example 5) Al2O3 powder was dispersed in ion-exchanged water, and a palladium nitrate (Pd(NO3)2) solution was added to the resulting Al2O3 aqueous dispersion at a Pd:Al2O3 = 1.0:100 (mass ratio). The resulting suspension was then evaporated to dryness. The resulting powder was calcined in air at 500 °C for 2 hours to prepare a Pd(1)-supported Al2O3(100) catalyst powder containing no CZL.

[0077] (Comparative Example 6) A Pd(2)-supported Al2O3(100) catalyst powder containing no CZL was prepared in the same manner as in Comparative Example 5, except that the amount of palladium nitrate (Pd(NO3)2) solution added was changed so that the mass ratio of Pd:Al2O3 was 2.0:100.

[0078] <Particle size distribution measurement> The volumetric particle size distribution of dispersed particles in the precious metal-containing raw salt water dispersions using the precious metal-containing colloidal solutions prepared in Examples 1 to 15, Comparative Examples 1 and 4, and the Pd colloidal solution prepared in Comparative Example 3 was measured by dynamic light scattering using a dynamic light scattering measurement device ("Zetasizer Nano ZSP" manufactured by Malvern Instruments). Note that the measurement sample was prepared by diluting the prepared colloidal solution or aqueous dispersion three times with ion-exchanged water adjusted to the same pH value as the colloidal solution or aqueous dispersion.

[0079] On the other hand, the volume-based particle size distribution of the dispersed particles in the precious metal-containing raw salt water dispersion by coprecipitation prepared in Comparative Example 2 was measured by the laser diffraction / scattering method using a laser diffraction / scattering particle size distribution measuring device (MT3000EX manufactured by Microtrack Bell Corporation) because the particle size range of the dispersed particles was outside the applicable range of the dynamic light scattering method.

[0080] The cumulative 50% diameter (D50) and cumulative 90% diameter (D90) were determined based on the volume-based particle size distribution obtained. These results are shown in Table 1.

[0081] [Table 1]

[0082] As shown in Table 1, a composite precursor nanocolloidal solution containing a precursor of a composite oxide of Ce, Zr, and the rare earth element X (CZX composite oxide) was prepared by mixing a raw salt aqueous solution containing a Ce salt, a Zr salt, and a salt of a rare earth element X other than Ce with a neutralizing aqueous solution containing a dispersant and neutralizing the raw salt aqueous solution. Furthermore, it was confirmed that the precious metal-containing colloidal solutions (Examples 1 to 15) obtained by adding a precious metal salt to the composite precursor nanocolloidal solution had the predetermined cumulative 90% diameter (D90) and cumulative 50% diameter (D50).

[0083] On the other hand, the precious metal-containing raw salt water dispersion containing the hydroxides of Pd, Ce, Zr, and La prepared by coprecipitation (Comparative Example 2) was found to contain particles on the order of micrometers.Furthermore, the precious metal-containing raw salt water dispersion prepared using a precious metal colloid solution containing polyethyleneimine as a protective agent (Comparative Example 3) was found to contain particles on the order of submicrons to microns.

[0084] <Durability test> Each catalyst powder prepared in Examples 1 to 6 and Comparative Examples 1 to 6 was pressed under a pressure of 1000 kg / cm using an isostatic press. 2The resulting green compact was crushed and sized to obtain catalyst pellets with a particle size of 0.5 to 1.0 mm.

[0085] 1.5 g of the obtained catalyst pellets was packed into a reaction tube with an inner diameter of 1.3 cm, and the temperature was 800°C and the flow rate was 500 cm 3 A five-hour durability test was conducted under the conditions of / min, with rich gas [H2 (2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance)] and lean gas [O2 (1 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance)] flowing alternately for five minutes each.

[0086] <Oxygen supply performance evaluation test> After the durability test, the catalyst was packed in the amount shown in Table 2 into a reaction tube with an inner diameter of 10 mm (No. 1) or a reaction tube with an inner diameter of 11 mm (No. 2), and set in a fixed-bed flow-type catalytic activity evaluation apparatus.

[0087] [Table 2]

[0088] Catalyst gas temperature: 450°C, flow rate: 1000cm 3 The catalyst was pretreated by alternately flowing 1 vol% O2 gas (balance: N2) for 90 seconds and 2 vol% CO gas (balance: N2) for 150 seconds under conditions of 1 / min. The catalyst inlet gas temperature was then lowered to 300°C, and the average oxygen supply rate per unit mass of catalyst was calculated from the amount of CO2 generated in 5 seconds after switching from 1 vol% O2 gas (balance: N2) to 2 vol% CO gas (balance: N2). The oxygen supply rate per unit mole of Ce was also calculated from the amount of CO2 generated in 30 seconds.

[0089] <Purification performance evaluation test> After the oxygen supply performance evaluation test, the catalyst inlet gas temperature was lowered to 100°C and the flow rate was increased to 1000 cm 3The evaluation gas [C3H6 (0.1 vol%) + CO (0.52 vol%) + O2 (0.55 vol%) + NO (0.3 vol%) + CO2 (14 vol%) + H2O (3 vol%) + N2 (balance)] was passed through the catalyst at a flow rate of 1 / min, and the temperature was raised to 500°C to determine the C3H6 conversion efficiency and NOx conversion efficiency. The NOx conversion efficiency was also determined at the catalyst inlet gas temperature HC-T50 when the C3H6 conversion efficiency reached 50%, and at a catalyst inlet gas temperature of 400°C.

[0090] Tables 3 and 4 show the average oxygen supply rate over 5 seconds, the oxygen supply amount over 30 seconds, and the catalyst inlet gas temperature HC-T50 at which the C3H6 conversion rate reached 50%. Table 5 shows the NOx conversion rate at a catalyst inlet gas temperature of 400°C.

[0091] [Table 3]

[0092] [Table 4]

[0093] [Table 5]

[0094] As shown in Table 3, the catalysts containing the rare earth element La in addition to Ce and Zr (Examples 1 and 6) had lower HC-T50 values ​​after the durability test than the catalyst not containing the rare earth element X other than Ce (Comparative Example 1), confirming that they had excellent low-temperature purification performance. Furthermore, the high oxygen supply rate and large oxygen supply amount confirmed that they had excellent low-temperature oxygen supply performance. Therefore, it was confirmed that the exhaust gas purification catalyst prepared using the precious metal-containing colloidal solution of the present invention is an excellent catalyst with high heat resistance.

[0095] As shown in Table 4, even when catalysts of the same composition were used, the catalyst prepared using the precious metal-containing colloidal solution of the present invention (Example 1) had a lower HC-T50 after the durability test than the catalyst prepared by the coprecipitation method (Comparative Example 2) and the catalyst prepared using a precious metal colloidal solution containing polyethyleneimine as a protective agent (Comparative Example 3), demonstrating excellent low-temperature purification performance, and also demonstrating excellent low-temperature oxygen supply performance due to its high oxygen supply rate and large oxygen supply amount. Therefore, it was confirmed that the exhaust gas purification catalyst prepared using the precious metal-containing colloidal solution of the present invention is an excellent catalyst with high heat resistance.

[0096] As shown in Table 5, Comparative Example 4, which contains a low amount of precious metal, does not achieve a high NOx purification rate even though it contains a CZX composite oxide. However, when Example 1 and Comparative Example 5, or Example 2 and Comparative Example 6, which contain predetermined and equivalent amounts of precious metal, are compared, it is confirmed that when the CZX composite oxide is contained, the NOx purification rate at the same temperature (e.g., 400°C) is higher than when the CZX composite oxide is not contained (Example 1 compared to Comparative Example 5, or Example 2 compared to Comparative Example 6), resulting in a catalyst with excellent purification performance. Furthermore, Example 1 exhibited a high NOx purification rate equal to or higher than Comparative Example 6, which contains twice the amount of precious metal, demonstrating that the inclusion of a CZX composite oxide provides excellent purification performance. In the examples, when the content of precious metal was increased (Example 2 was higher than Example 1, and Example 3 was higher than Example 2) or when the amount of precious metal-containing colloid supported was increased (Example 4 was higher than Example 2, and Example 5, in which the amount of precious metal was halved, was higher than Example 3), and it was confirmed that even after exposure to high temperatures, pore blockage by the precious metal and CZX composite oxide was suppressed and the precious metal and CZX composite oxide were retained in a highly dispersed state, making this an excellent catalyst with high heat resistance. [Industrial Applicability]

[0097] As described above, the present invention makes it possible to obtain a precious metal-containing colloidal solution containing a nanoscale CZX composite oxide precursor. Use of the precious metal-containing colloidal solution of the present invention makes it possible to realize a structure in which nanoscale CZX composite oxide particles are supported on a carrier and a precious metal is disposed on the surface of the nanoscale CZX composite oxide particles. The precious metal-containing colloidal solution of the present invention is useful as a raw material for producing an exhaust gas purification catalyst having such a structure. The exhaust gas purification catalyst obtained in this manner exhibits excellent purification performance for purifying harmful components emitted from internal combustion engines such as automobile engines.

Claims

1. Contains a precious metal, Ce, Zr, and at least one rare earth element other than Ce, The colloidal particles have a cumulative 90% diameter (D90) of 20 nm or less in the volume-based particle size distribution, The content of the noble metal is 0.5 to 110 parts by mass per 100 parts by mass of the composite oxide of Ce, Zr, and the rare earth element. A precious metal-containing colloidal solution.

2. 2. The noble metal-containing colloidal solution according to claim 1, wherein the colloidal particles have a cumulative 50% diameter (D50) in a volume-based particle size distribution of 1 to 15 nm.

3. 2. The precious metal-containing colloidal solution according to claim 1, further comprising at least one dispersant selected from the group consisting of monoethanolamine, diethanolamine, ethylenediamine, glycine, hexaaminocaproic acid, polyethyleneimine, cetyltrimethylammonium bromide, polyvinylpyrrolidone, ammonium polyacrylate, and ammonium salt-based carboxylic acid copolymers.

4. preparing a raw salt aqueous solution containing a Ce salt, a Zr salt, and a salt of at least one rare earth element other than Ce; preparing an aqueous neutralization solution containing a dispersant; The raw salt aqueous solution and the neutralization aqueous solution were mixed at a shear rate of 100 sec －１ a step of mixing the above and neutralizing the raw salt aqueous solution to prepare a nanocolloidal solution of a composite precursor containing a precursor of a composite oxide of Ce, Zr, and the rare earth element; adding a noble metal salt to the composite precursor nanocolloidal solution to prepare a noble metal-containing colloidal solution containing the noble metal and the composite precursor nanocolloidal particles; 2. A method for producing a precious metal-containing colloidal solution, comprising:

5. 5. The method for producing a precious metal-containing colloidal solution according to claim 4, wherein the raw salt aqueous solution further contains a dispersant.

6. 6. The method for producing a precious metal-containing colloidal solution according to claim 4, wherein the dispersant is at least one selected from the group consisting of monoethanolamine, diethanolamine, ethylenediamine, glycine, hexaaminocaproic acid, polyethyleneimine, cetyltrimethylammonium bromide, polyvinylpyrrolidone, ammonium polyacrylate, and ammonium salt-based carboxylic acid copolymers.

7. 4. A catalyst for purifying exhaust gas, comprising: a carrier loaded with the composite oxide of Ce, Zr, and the rare earth element; and a precious metal-containing colloidal solution according to claim 1.

8. A method for producing an exhaust gas purifying catalyst, comprising adhering the noble metal-containing colloidal solution according to any one of claims 1 to 3 to a carrier, and then calcining the carrier.

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