Core-shell support, method for its production, catalyst for exhaust gas purification using the core-shell support, method for its production, and method for exhaust gas purification using the catalyst for exhaust gas purification

Abstract

Core-shell support, comprising: a core comprising at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions; and a shell comprising a rare earth zirconium oxide-based composite oxide represented by a composition formula: (R 1-x Ce x )2Zr2O 7+x , where R represents a rare earth element which is at least one element selected from the group consisting of La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y, and x represents a number from 0.0 to 0.8, and with which an outer side of the core is coated, wherein the rare earth zirconium oxide-based composite oxide contains crystal particles having a pyrochlore structure, and the composite oxide based on rare earth zirconium oxide has an average crystal diameter of 3 to 9 nm, wherein an amount of the rare earth zirconium oxide-based composite oxide forming the shell is 4 to 24 parts by mass based on 100 parts by mass of the at least one oxygen storage / release material forming the core.

Description

[Technical field of invention]

[0001] The present invention relates to a core-shell support, a method for producing the core-shell support, a catalyst for purifying exhaust gas using the core-shell support, a method for producing the catalyst, and a method for purifying exhaust gas using the catalyst for purifying exhaust gas. [General state of the art]

[0002] Three-way catalysts, oxidation catalysts, NOx storage catalysts, and the like, which serve as exhaust gas purification catalysts for motor vehicles and the like, have been developed since the past to remove harmful components contained in exhaust gases, such as harmful gases (hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (NOx)). In addition to the recent increase in environmental awareness, regulations on exhaust gases emitted by motor vehicles and the like have been further tightened, and the improvement of these catalysts has been promoted accordingly.

[0003] As such an exhaust gas purification catalyst, Japanese Unexamined Patent Application JP 2007-144290 A1 (Patent Document 1) discloses an exhaust gas purification catalyst comprising: noble metal particles containing at least rhodium particles; an oxygen storage / release material particle; and a carrier oxide, such as ZrO2 or TiO2, which is present between the noble metal particles and the oxygen storage / release material particle and which supports the noble metal particles on a surface separated from the oxygen storage / release material particle. The exhaust gas purification catalyst comprises a carrier having a core-shell structure in which the oxygen storage / release material particle forms a core part and the carrier oxide forms a shell part covering the oxygen storage / release material particle.and the noble metal particles are in contact with an outer surface of the carrier oxide of the support. In the exhaust gas purification catalyst disclosed in Patent Document 1, the carrier oxide, such as ZrO2 or TiO2, covers the entire core element made of the oxygen storage / release material (OSC material), such as CeO2. However, with this structure, the oxygen storage / release capacity provided by the core element is greatly reduced, and the oxygen storage / release capacity (OSC) is not necessarily sufficient.

[0004] For a catalyst for exhaust gas purification, WO 2005 / 102 524 A1 (patent document 2) discloses a metal oxide consisting of a core part and a surface layer.

[0005] Furthermore, since exhaust gas purification catalysts are increasingly required to have advanced properties recently, there is a need for exhaust gas purification catalyst supports and exhaust gas purification catalyst that offer such highly advanced catalytic performance so that both oxygen storage / release capacity (OSC) and NOx removal activity can be sufficiently demonstrated. [Citation list][Patent specifications] [PTL 1] JP 2007-144 290 A1 [PTL 2] WO 2005 / 102 524 A1 [Brief description of the invention][Technical problem]

[0006] The present invention has been made in view of the above-described problems of conventional technologies, and an object of the present invention is to provide a core-shell support enabling both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity to be exhibited, a process for producing the core-shell support, a catalyst for exhaust gas purification using the core-shell support, a process for producing the catalyst, and a process for exhaust gas purification using the catalyst for exhaust gas purification. [Solution to the problem]

[0007] The above-mentioned object is achieved by the subject matter of the independent claims. Advantageous embodiments of the present invention are the subject matter of the dependent claims.

[0008] The present inventors have conducted intensive research to solve the above-described problem and thus discovered the following fact. Specifically, it is possible for a core-shell support to include: a core containing at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions;and a shell containing a rare earth-zirconium oxide composite oxide having a specific composition and coated on an outer surface of the core, wherein the rare earth-zirconium oxide composite oxide contains crystal particles having a pyrochlore structure, and the average crystal diameter of the rare earth-zirconium oxide composite oxide is within a specific range; a core-shell support that enables both oxygen storage / release capacity (OSC) and NOx removal activity to be sufficiently exhibited; a method for producing the core-shell support, a catalyst for exhaust gas purification using the core-shell support, a method for producing the catalyst, and an exhaust gas purification method using the catalyst for exhaust gas purification. This result has led to the completion of the present invention.

[0009] The core-shell carrier of the present invention comprises: a core comprising at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions; and a shell comprising a rare earth zirconium oxide-based composite oxide represented by a composition formula: (R 1-x Ce x )2Zr2O 7+x , where R represents a rare earth element which is at least one element selected from the group consisting of La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y, and x represents a number from 0.0 to 0.8, and with which an outer side of the core is coated, wherein the rare earth zirconium oxide-based composite oxide contains crystal particles having a pyrochlore structure, and the composite oxide based on rare earth zirconium oxide has an average crystal diameter of 3 to 9 nm, wherein an amount of the rare earth zirconium oxide-based composite oxide forming the shell is 4 to 24 parts by mass based on 100 parts by mass of the at least one oxygen storage / release material forming the core.

[0010] In the core-shell carrier of the present invention, x in the composition formula is preferably a number from 0.5 to 0.7.

[0011] In addition, in the core-shell support of the present invention, R in the composition formula is preferably at least one element selected from the group consisting of La, Nd, Pr and Y.

[0012] A first exhaust gas purification catalyst of the present invention is a catalyst comprising: the above-described core-shell support of the present invention; and a noble metal supported on the core-shell support. In the first exhaust gas purification catalyst of the present invention, the noble metal is preferably Rh.

[0013] A second catalyst for exhaust gas purification of the present invention comprises: a substrate; and a catalyst layer disposed on the substrate, wherein the catalyst layer comprises the core-shell support of the present invention, alumina, and a noble metal. Also in the second catalyst for exhaust gas purification of the present invention, the noble metal is preferably Rh.

[0014] In addition, in the second catalyst for exhaust gas purification of the present invention, it is preferable that (1) at least a part of the precious metal is supported on the core-shell carrier and / or (2) the catalyst layer further comprises a zirconium oxide-based support and at least a part of the noble metal is supported on the zirconium oxide-based support.

[0015] Furthermore, in the second exhaust gas purification catalyst of the present invention, it is preferable that the catalyst layer comprising the core-shell support, the alumina, and the noble metal is a rhodium-containing catalyst layer containing Rh as the noble metal, and that a palladium-containing catalyst layer containing an alumina-doped ceria-zirconia-alumina-Pd-based solid solution is disposed between the substrate and the rhodium-containing catalyst layer.

[0016] A method for producing the core-shell carrier of the present invention is a method for producing the above-described core-shell carrier of the present invention, the method comprising: a solution preparation step of preparing a solution containing a rare earth element salt and a zirconium salt; a first coating step of bringing the prepared solution into contact with a powder of at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina to obtain a core-shell powder supporting the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth-zirconia-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding; and a second coating step to bring the prepared solution into contact with the obtained core-shell powder to obtain the core-shell powder which additionally supports the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth zirconium oxide-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding, wherein the core-shell support is obtained by performing the second coating step until an amount of the rare earth zirconium oxide-based composite oxide constituting the shell after calcination into the oxide reaches 4 to 24 parts by mass based on 100 parts by mass of the oxygen storage / release material constituting the core.

[0017] A method for producing a catalyst for exhaust gas purification of the present invention is a method for producing the above-described first catalyst for exhaust gas purification of the present invention, the method comprising: a solution preparation step of preparing a solution containing a rare earth element salt and a zirconium salt; a first coating step of bringing the prepared solution into contact with a powder of at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina to obtain a core-shell powder supporting the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth-zirconia-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding; and a second coating step to bring the prepared solution into contact with the obtained core-shell powder to obtain a core-shell powder that additionally supports the prepared solution in an amount that, after calcination into an oxide, results in an amount of 1 to 8 parts by mass of the rare earth zirconium oxide-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding, wherein the core-shell support is obtained by performing the second coating step until an amount of the shell-forming rare earth zirconium oxide-based composite oxide after calcination into the oxide reaches 4 to 24 parts by mass based on 100 parts by mass of the core-forming oxygen storage / release material, and then the catalyst for exhaust gas purification is obtained by bringing a precious metal salt solution into contact with the core-shell carrier.

[0018] A method for purifying exhaust gas of the present invention is a method comprising purifying an exhaust gas emitted from an internal combustion engine by bringing the exhaust gas into contact with the above-described catalyst for purifying exhaust gas of the present invention.

[0019] It should be noted that although it is not exactly clear why the catalyst of the present invention achieves the above-described object, the present inventors conjecture as follows. Specifically, since the noble metal such as Rh is supported on the oxygen storage / release material such as CeO2 in the conventional catalyst, the conversion of the noble metal to its metallic state is inhibited, and exhaust gas purification activities, particularly NOx removal activity, are reduced. However, an oxygen storage / release (OSC) material mainly containing CeO2 or the like is necessary in a three-way catalyst. In other words, improving the NOx removal activity of a Rh catalyst and providing OSC are considered to be in a trade-off relationship.

[0020] In the present invention, the core-shell support comprises: the core containing at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions; and the shell containing a rare earth-zirconia-based composite oxide represented by the composition formula: (R1- x Ce x )2Zr2O 7+x, where R represents a rare earth element which is at least one element selected from the group consisting of La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y, and x represents a number from 0.0 to 0.8), and with which an outer side of the core is coated. In addition, the rare earth-zirconium oxide composite oxide contains crystal particles having a pyrochlore structure, and the average crystal diameter of the rare earth-zirconium oxide composite oxide is limited to the range of 3 to 9 nm, wherein an amount of the rare earth-zirconium oxide composite oxide constituting the shell is 4 to 24 parts by mass relative to 100 parts by mass of the oxygen storage / release material constituting the core.

[0021] Thus, in the core-shell carrier obtained, Ce-poor material (R 1-x Ce x )2Zr2O 7+xcontaining R2Zr2O7, stabilized by the pyrochlore structure, as the shell on the Ce-rich OSC material serving as the core (at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions). The present inventors speculate that supporting the noble metal on such a core-shell support improves the reducibility of the noble metal, enabling a further improvement in NOx removal activity compared to a noble metal-supporting OSC material.In addition, the present inventors conjecture that the NOx removal activity and the oxygen storage / release capacity, which are conventionally considered to be in a trade-off relationship, can be simultaneously achieved at a high level, this makes it possible to provide a core-shell support showing both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity, a method for producing the core-shell support, a catalyst for exhaust gas purification using the core-shell support, a method for producing the catalyst, and a method for exhaust gas purification using the catalyst for exhaust gas purification. [Advantageous effects of the invention]

[0022] According to the present invention, it is possible to provide a core-shell support exhibiting both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity, a process for producing the core-shell support, a catalyst for exhaust gas purification using the core-shell support, a process for producing the catalyst, and a process for exhaust gas purification using the catalyst for exhaust gas purification. [Brief description of the drawings] Fig. 1 is a graph showing the 50% NOx removal temperatures (NOx_T50) of catalysts obtained in Non-inventive Examples 1 to 4, Inventive Examples 5 and 6, and Non-inventive Comparative Examples 1 to 4. Fig.2 is a graph showing the transient NOx removal ratios of the catalysts obtained in Non-inventive Examples 1 to 4, Inventive Examples 5 and 6, and Non-inventive Comparative Examples 1 to 4. Fig. 3 is a graph showing the OSC rates of the catalysts obtained in Non-Inventive Examples 1 to 4, Inventive Examples 5 and 6, and Non-Inventive Comparative Examples 1 to 4. Fig. Figure 4 shows curves illustrating the maximum oxygen storage capacity (OSC) and NOx emission of catalysts from Inventive Examples 7 to 9 and Noninventive Comparative Examples 5 to 7 (after accelerated deterioration treatment). Note that the bars indicate the maximum oxygen storage capacity (OSC) and the lines indicate NOx emission. [Description of embodiments]

[0023] The present invention will be described in detail below based on preferred embodiments. [Core-shell-carrier]

[0024] A core-shell carrier of the present invention is described. The core-shell carrier of the present invention comprises: a core containing at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions; and a shell containing a rare earth zirconium oxide-based composite oxide represented by a composition formula: (R 1-x Ce x )2Zr2O 7+x, where R represents a rare earth element which is at least one element selected from the group consisting of La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y, and x represents a number from 0.0 to 0.8, and with which an outer side of the core is coated, wherein the rare earth zirconium oxide-based composite oxide contains crystal particles with a pyrochlore structure, and the composite oxide based on rare earth zirconium oxide has an average crystal diameter of 3 to 9 nm, wherein an amount of the rare earth zirconium oxide-based composite oxide constituting the shell is 4 to 24 parts by mass relative to 100 parts by mass of the oxygen storage / release material constituting the core. (Core)

[0025] The core in the core-shell support of the present invention must contain at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions. The core of the core-shell support of the present invention has an oxygen storage / release capacity (OSC).

[0026] The ceria-zirconia-based solid solution in the core of the core-shell support of the present invention is not particularly limited, and specific examples thereof include CeO2-ZrO2 solid solutions, CeO2-ZrO2-La2O3 solid solutions, CeO2-ZrO2-La2O3-Y2O3 solid solutions, CeO2-PrO2-ZrO2-La2O3-Y2O3 solid solutions, CeO2-ZrO2-La2O3 solid solutions, CeO2-ZrO2-PrO2 solid solutions, and CeO2-ZrO2-La2O3-Y2O3-Nd2O3 solid solutions. Particularly from the viewpoints of OSC performance and heat resistance, the ceria-zirconia-based solid solution is preferably at least one selected from the group consisting of CeO2-ZrO2 solid solutions, CeO2-ZrO2-La2O3 solid solutions, CeO2-ZrO2-La2O3-Y2O3 solid solutions, and CeO2-ZrO2-PrO2 solid solutions.

[0027] Meanwhile, the alumina-doped ceria-zirconia-based solid solution in the core of the core-shell support of the present invention is not particularly limited, and specific examples thereof include Al2O3-doped CeO2-ZrO2 solid solutions, Al2O3-doped CeO2-ZrO2-La2O3 solid solutions, Al2O3-doped CeO2-ZrO2-La2O3-Nd2O3 solid solutions, and Al2O3-doped CeO2-ZrO2-PrO2-La2O3-Y2O3 solid solutions. Particularly from the viewpoints of OSC performance and heat resistance, the alumina-doped ceria-zirconia-based solid solution is preferably at least one selected from the group consisting of Al2O3-doped CeO2-ZrO2 solid solutions, Al2O3-doped CeO2-ZrO2-La2O3 solid solutions, and Al2O3-doped CeO2-ZrO2-La2O3-Y2O3-Nd2O3 solid solutions.

[0028] The alumina-doped ceria-zirconia-based solid solution preferably contains 10 to 70% by mass of Al2O3, 10 to 70% by mass of CeO2, and 30 to 80% by mass of ZrO2, based on the total mass of the solid solution. When the alumina-doped ceria-zirconia-based solid solution contains metal oxides other than Al2O3, CeO2, and ZrO2, it is additionally preferable that the metal oxides are each independently contained in a ratio of 0.5 to 10% by mass, based on the total mass of the solid solution.

[0029] It is preferable that, as the alumina-doped ceria-zirconia-based solid solution, a solid solution in which ceria and zirconia are mixed with each other at the atomic level and doped with alumina in an amorphous form or in the form of γ-alumina or θ-alumina is used from the viewpoint of sufficiently forming an ordered phase. In addition, the alumina-doped ceria-zirconia-based solid solution preferably has an average primary particle diameter of 10 nm or less. If the average CeO2-ZrO2 primary particle diameter of the alumina-doped ceria-zirconia-based solid solution exceeds the upper limit, the OSC performance, especially the OSC reaction rate, tends to be insufficient.

[0030] In addition, the use of the alumina-doped ceria-zirconia-based solid solution as the core according to the core-shell support of the present invention is preferable because, further, a surface layer enriched with R2Zr2O7 is formed on a part of an alumina surface, so that, for example, the deactivation of the noble metal such as Rh in an oxidizing atmosphere due to the embedding of the noble metal in the alumina can be prevented.

[0031] Furthermore, from the viewpoint of improving the heat resistance of the support and the catalytic activity of the noble metal, the core according to the core-shell support of the present invention (at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina) may be appropriately doped with dopants unless an effect of the present invention is impaired.It is possible to use as the dopants, for example, any oxide of metals, including rare earths, alkali metals, alkaline earth metals, transition metals and the like, such as lanthanum (La), yttrium (Y), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc) and vanadium (V), mixtures of oxides of these metals, solid solutions of oxides of these metals, composite oxides of these metals, as appropriate.

[0032] In addition, a secondary particle diameter (aggregate particle diameter) of at least one oxygen storage / release material of the core of the core-shell support of the present invention selected from alumina-doped ceria-zirconia-based solid solutions is not particularly limited, and the secondary particle diameter is particularly about 100 nm to 100 μm, and from the viewpoint of use as a coating layer of a catalyst for exhaust gas purification, preferably in a range of 100 nm to 10 μm.

[0033] Furthermore, the shape of the core is not particularly limited, and the core is preferably in powder form. Additionally, it is possible to use a material selected from alumina-doped ceria-zirconia-based solid solutions alone or two selected from them together as the core.

[0034] Furthermore, a method for producing such an alumina-doped ceria-zirconia-based solid solution is not particularly limited, and a known method can be used as appropriate. Furthermore, commercially available materials can be used as the ceria-zirconia-based solid solution or the alumina-doped ceria-zirconia-based solid solution. (Peel)

[0035] Next, the shell of the core-shell support of the present invention must contain a rare earth zirconium oxide-based composite oxide represented by the following composition formula: (R 1-x Ce x )2Zr2O 7+x, where R represents a rare earth element, which is at least one element selected from the group consisting of La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y, and x represents a number from 0.0 to 0.8. If x in the composition formula of the rare earth zirconia-based composite oxide exceeds the upper limit, the composite oxide is so rich in Ce that the conversion of the noble metal, such as Rh, to its metallic state is prevented. This lowers the catalytic activity, so that sufficient NOx removal activity cannot be achieved.From the viewpoint of obtaining a core-shell support which offers both sufficiently high oxygen storage / release capacity (OSC) and sufficiently high NOx removal activity, and which exhibits sufficiently good oxygen storage / release capacity (OSC) even after being exposed to high temperatures for a long period of time, x is preferably a number between 0.1 and 0.8, and particularly preferably a number of 0.5 to 0.7.

[0036] It should be noted that the composition of the rare earth zirconium oxide-based composite oxide can be determined by composition analysis based on ICP emission spectroscopy (plasma emission spectroscopy) using an inductively coupled plasma (ICP) emission spectrometer or composition analysis using any one or a suitable combination of any of the following: an X-ray fluorescence analyzer (XRF: X-ray fluorescence analysis), an EDX (energy dispersive X-ray spectrometer), an XPS (X-ray photoelectron spectrometer), a SIMS (secondary ion mass spectrometer), an HRTEM (high-resolution transmission electron microscope), an FE-STEM (field emission scanning transmission electron microscope), and the like.In particular, after the powder is dissolved in an acid, for example, a composition analysis is carried out by measuring the weight ratio of cation species in the obtained solution by ICP emission spectroscopy to perform the composition analysis of the rare earth zirconium oxide-based composite oxide.

[0037] Additionally, R in the composition formula of the rare earth zirconia composite oxide must be a rare earth element. Specific examples of R include lanthanum (La), neodymium (Nd), praseodymium (Pr), cerium (Ce), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), and yttrium (Y). The rare earth zirconia composite oxide may contain one of these elements alone or two or more of them together.From the viewpoint of material price and NOx removal activity, of these elements R in the composition formula of the rare earth zirconia-based composite oxide, it is preferable to contain at least one element selected from the group consisting of lanthanum (La), neodymium (Nd), praseodymium (Pr), and yttrium (Y), and more preferably to contain at least one element selected from the group consisting of La, Nd, and Y.

[0038] In addition, the rare earth zirconium oxide-based composite oxide according to the core-shell support of the present invention must contain crystal particles with a pyrochlore structure in the shell. The phrase "the rare earth zirconium oxide-based composite oxide has a pyrochlore structure" means that R ions, cerium ions, and zirconium ions in the composition formula form a crystal phase (pyrochlore phase) with a regularly arranged pyrochlore-type structure. The pyrochlore RCZ has oxygen defect sites. When oxygen atoms enter these sites, the pyrochlore phase undergoes a phase transition into a κ phase (kappa phase). Meanwhile, the κ phase can undergo a phase transition into the pyrochlore phase by releasing oxygen atoms.A rare earth zirconium oxide composite oxide with a pyrochlore structure exhibits oxygen storage / release (OSC) performance based on the above-described change in the number of oxygen atoms in the crystal lattice. Note that the crystal phase of the rare earth zirconium oxide composite oxide can be determined by X-ray diffraction (XRD) measurement using CuKα radiation. The pyrochlore phase can be confirmed by examining a characteristic peak at approximately 2θ = 14.2° (degrees) in an XRD pattern of the rare earth zirconium oxide composite oxide.

[0039] In addition, the rare earth-zirconium oxide composite oxide in the shell according to the core-shell support of the present invention must have an average crystal diameter in a range of 3 to 9 nm. Consider a case where the average crystal diameter of the rare earth-zirconium oxide composite oxide is smaller than the lower limit. If a catalyst is prepared by supporting a noble metal on such a rare earth-zirconium oxide composite oxide, the noble metal (Rh or the like) is difficult to reduce due to the interaction between CeO2 and the noble metal (Rh or the like), so the NOx removal activity decreases and the NOx removal performance cannot be sufficiently achieved. Meanwhile, if the average crystal diameter exceeds the upper limit, a problem arises that the OSC performance is significantly lowered.In addition, from the viewpoint of obtaining a core-shell support that offers both sufficiently high oxygen storage / release capacity (OSC) and sufficiently high NOx removal activity, and that exhibits sufficiently good oxygen storage / release capacity (OSC) even after being exposed to high temperatures for a long period of time, the average crystal diameter of the rare earth zirconium oxide-based composite oxide is preferably 1 to 20 nm. Note that the crystal diameter can be determined, for example, by a method in which the crystal diameter is determined by an analysis based on X-ray powder diffraction, a method in which the crystal diameter is determined by observation under a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like.For example, when the crystal diameter is determined by X-ray powder diffraction, the rare earth zirconium oxide-based composite oxide is analyzed by X-ray powder diffraction, and a half width B. nkl (rad) of the diffraction peak value of a predetermined crystal plane (hkl) is obtained from the obtained diffraction pattern. Then, an average value D hkl (nm) the crystal diameter in a direction perpendicular to the (hkl-) crystal plane of the rare earth zirconium oxide composite oxide particles can be calculated using the Scherrer equation: D hkl = Kλ / B hkl cosθ hkl . In the Scherrer equation, the constant K is 0.9, λ is a wavelength (nm) of the X-rays, and θ hkl is a diffraction angle (degrees, °). In addition, the term “mean crystal diameter” refers to an average value D 440(nm) is the crystal diameter in a direction perpendicular to the (440) plane, which is a value determined by X-ray powder diffraction.

[0040] Furthermore, the amount of the rare earth-zirconia-based composite oxide supported on the core in the core-shell support of the present invention is 4 to 24 parts by mass, and preferably 8 to 18 parts by mass, based on 100 parts by mass of the core (at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions). If the amount of the supported active component is less than the lower limit, the obtained catalytic activity tends to be insufficient, and the NOx removal activity tends to decrease. Meanwhile, if the amount of the supported active component exceeds the upper limit, the cost of the catalyst tends to increase, and the activity of the catalyst (OSC) tends to decrease.In addition, a method for supporting the rare earth-zirconium oxide composite oxide on the core is not particularly limited, and any known method for supporting components of the rare earth-zirconium oxide composite oxide on the core can be used as appropriate. For example, a method can be used in which the core is impregnated with an aqueous solution containing salts of metals that are components of the rare earth-zirconium oxide composite oxide, followed by drying and calcination. [Catalysts for exhaust gas purification]

[0041] Next, exhaust gas purifying catalysts of the present invention will be described. (First catalyst for exhaust gas purification of the present invention)

[0042] A first catalyst for exhaust gas purification of the present invention includes: the above-described core-shell support of the present invention; and a noble metal supported on the core-shell support.

[0043] The noble metal in the exhaust gas purification catalyst of the present invention is not particularly limited, and examples thereof include platinum (Pt), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), gold (Au), and the like. One of these noble metals may be used alone, or two or more of them may be used together. Of these noble metals, platinum, rhodium, and palladium are preferable, and rhodium is particularly preferable from the viewpoint of obtaining an exhaust gas purification catalyst having both sufficiently high oxygen storage / release capacity (OSC) and sufficiently high NOx removal activity. The amount of the supported noble metal is not particularly limited and is adjusted as appropriate according to an application of the obtained catalyst or the like. The amount of the supported noble metal is preferably 0.05 to 10 parts by mass based on 100 parts by mass of the core-shell support.

[0044] In addition, a form of the exhaust gas purification catalyst of the present invention is not particularly limited, and the catalyst can be used, for example, in a form of particles as it is, or in a form of a honeycomb monolithic catalyst in which the catalyst is supported on a substrate, a form of a pellet catalyst obtained by forming the catalyst into pellets, or the like. Methods for producing catalysts in such forms are not particularly limited, and known methods can be employed as appropriate. For example, it is possible to employ, as appropriate, a method in which a pellet-shaped catalyst is obtained by forming the catalyst into pellets, a method in which the catalyst is obtained in a coated (solid) form on a catalyst substrate by coating the catalyst substrate with the catalyst, and the like.In addition, the catalyst substrate is not particularly limited and is selected as appropriate, for example, according to an application of the obtained catalyst or the like. A monolithic honeycomb-shaped substrate, a pellet-shaped substrate, a plate-shaped substrate, or the like is preferably used. In addition, a material of the catalyst substrate is not particularly limited, and, for example, a substrate made of a ceramic such as cordierite, silicon carbide, or mullite, or a substrate made of a metal such as stainless steel containing chromium and aluminum is preferably used. In addition, other components (for example, NOx storage material and the like) usable for various catalysts can be appropriately supported in the exhaust gas purifying catalyst of the present invention unless an effect of the catalyst is impaired. (Second catalyst for exhaust gas purification of the present invention)

[0045] A second catalyst for exhaust gas purification of the present invention includes: a substrate; and a catalyst layer disposed on the substrate, the catalyst layer containing the core-shell support of the present invention, alumina, and a noble metal.

[0046] In addition, in the second catalyst for exhaust gas purification of the present invention, it is preferable that (1) at least a part of the precious metal is supported on the core-shell carrier and / or (2) the catalyst layer further contains a zirconium oxide-based support and at least a part of the noble metal is supported on the zirconium oxide-based support.

[0047] The substrate in the second exhaust gas purification catalyst of the present invention is not particularly limited, and is selected as appropriate, for example, according to an application of the obtained catalyst or the like. A monolithic honeycomb-shaped substrate, a pellet-shaped substrate, a plate-shaped substrate, or the like is preferably used. In addition, a material of the catalyst substrate is not particularly limited, and, for example, a substrate made of a ceramic such as cordierite, silicon carbide, or mullite, or a substrate made of a metal such as stainless steel containing chromium and aluminum is preferably used.

[0048] The noble metal in the second exhaust gas purification catalyst of the present invention is not particularly limited, and examples thereof include platinum (Pt), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), gold (Au), and the like. One of these noble metals may be used alone, or two or more of them may be used together. Of these noble metals, platinum, rhodium, and palladium are preferable, and rhodium is particularly preferable from the viewpoint of obtaining an exhaust gas purification catalyst having both sufficiently high oxygen storage / release capacity (OSC) and sufficiently high NOx removal activity. The amount of the supported noble metal is not particularly limited and is adjusted as appropriate according to an application of the obtained catalyst or the like. The amount of the supported noble metal is preferably 0.05 to 10 parts by mass based on 100 parts by mass of the support.

[0049] The second exhaust gas purification catalyst of the present invention preferably contains 0.01 to 2.0 g / L of the noble metal, 50 to 180 g / L of the core-shell support of the present invention, and 20 to 150 g / L of alumina, each per liter of the capacity of the substrate.

[0050] In addition, when the second exhaust gas purification catalyst of the present invention further contains a zirconia-based carrier, the zirconia-based carrier is not particularly limited, and specific examples thereof may include carriers made of ZrO2 solid solutions, Al2O3-doped ZrO2 solid solutions, ZrO2-La2O3 solid solutions, Al2O3-doped ZrO2-La2O3 solid solutions, ZrO2-La2O3-Y2O3 solid solutions, Al2O3-doped ZrO2-La2O3-Y2O3 solid solutions, ZrO2-PrO2 solid solutions, and Al2O3-doped ZrO2-PrO2 solid solutions. In this case, the amount of the zirconia-based carrier is preferably 30 to 80 g / L per liter of the substrate capacity.

[0051] Additionally, in the second exhaust gas purification catalyst of the present invention, it is preferable that the catalyst layer comprising the core-shell support, alumina, and the noble metal be a rhodium-containing catalyst layer containing Rh as the noble metal, and that a palladium-containing catalyst layer containing an alumina-doped ceria-zirconia-based solid solution, alumina, and Pd be interposed between the substrate and the rhodium-containing catalyst layer. Such a palladium-containing catalyst layer preferably contains 0.01 to 2.0 g / L of palladium, 10 to 60 g / L of the alumina-doped ceria-zirconia-based solid solution, and 20 to 70 g / L of alumina, per liter of the substrate capacity. [Method for manufacturing the core-shell support]

[0052] Next, a method for manufacturing a core-shell carrier of the present invention will be described. The method for manufacturing a core-shell carrier of the present invention is a method for manufacturing the above-described core-shell carrier of the present invention, which comprises: a solution preparation step for preparing a solution containing a rare earth element salt and a zirconium salt; a first coating step of bringing the prepared solution into contact with a powder of at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina to obtain a core-shell powder supporting the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth-zirconia-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding; and a second coating step of bringing the prepared solution into contact with the obtained core-shell powder to obtain a core-shell powder which additionally supports the prepared solution in an amount which, after calcination into an oxide, results in an amount of 1 to 8 parts by mass of the rare earth zirconium oxide-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding, wherein the core-shell support is obtained by performing the second coating step until an amount of the rare earth zirconium oxide-based composite oxide forming the shell after calcination into the oxide reaches 4 to 24 parts by mass based on 100 parts by mass of the oxygen storage / release material forming the core. (Solution preparation step)

[0053] In the method for producing a core-shell carrier of the present invention, first, a solution containing a salt of a rare earth element and a zirconium salt is prepared (solution preparation step).

[0054] The rare earth element salt in the solution is not particularly limited, and examples include rare earth element salts such as nitrates, sulfates, halides (fluorides, chlorides, and the like), acetates, carbonates, and organic hydrogen salts (for example, citrates) of rare earth elements, and complex compounds thereof.

[0055] Of these salts, the rare earth element salt is preferably at least one selected from the group consisting of nitrates, acetates, carbonates, and citrates, from the viewpoints of uniform support to the core and cost, as well as from the viewpoint that components remaining in the shell during production can be removed relatively easily. The same rare earth elements as described for the core-shell support of the present invention can be used as the rare earth element in the solution.

[0056] Meanwhile, examples of the zirconium (Zr) salt in the solution include zirconium salts such as nitrates (for example, zirconium oxynitrate and zirconyl oxynitrate), sulfates, halides (fluorides, chlorides, and the like), acetates, carbonates, and zirconium citrates, and complex compounds thereof. Among these zirconium salts, it is preferable to use at least one selected from the group consisting of nitrates and acetates as the Zr salt from the viewpoints of uniform support on the core and cost, and from the viewpoint that components remaining in the shell during manufacturing can be relatively easily removed.

[0057] In addition, a solvent is not particularly limited, and examples thereof include water (preferably pure water such as ion-exchanged water or distilled water) and the like.

[0058] It should be noted that the concentrations in the solution containing a salt of a rare earth element and a zirconium salt are not particularly limited, and the concentration of the rare earth element ions is preferably in a range of 0.001 to 0.1 mol / L, and the concentration of zirconium (Zr) ions is preferably in a range of 0.001 to 0.1 mol / L. (First coating step)

[0059] Next, the prepared solution is brought into contact with a powder of at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions to obtain a core-shell powder supporting the prepared solution in an amount that, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth-zirconia-based composite oxide constituting a part of the shell, based on 100 parts by mass of the oxygen storage / release material constituting the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding (first coating step).

[0060] A method for bringing the solution into contact with the powder of at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina is not particularly limited, and it is possible to use, as appropriate, a known method in which the solution can be supported on the powder by adsorption, such as a method in which the powder is impregnated with the solution, a method in which the solution is supported on the powder by adsorption, a method in which the solution is impregnated with the powder, or the like.

[0061] When the solution is brought into contact with the oxygen storage / release material powder as described above, it is additionally necessary to support the solution in an amount that, after calcination into an oxide, results in 1 to 8 mass parts of the rare earth zirconium oxide-based composite oxide constituting part of the shell, based on 100 mass parts of the oxygen storage / release material constituting the core. If the amount of the supported solution is less than the lower limit, it is difficult to exhibit sufficient catalytic activity. However, if the amount of the supported solution exceeds the upper limit, the solution is unevenly supported or the composition becomes uneven, thus reducing the catalytic activity.It should be noted that, from the viewpoint of supporting the solution with a uniform support density, the amount of the supported solution is preferably an amount that, after calcination into an oxide, gives 2 to 6 mass parts, and further preferably an amount that, after calcination into an oxide, gives 4 to 6 mass parts of the rare earth-zirconium oxide composite oxide constituting a part of the shell, based on 100 mass parts of the oxygen storage / release material constituting the core.

[0062] In addition, a heating condition for calcination must be in a temperature range of 600 to 1100 °C. If the heating temperature for calcination is lower than the lower limit, a pyrochlore phase, which is a desirable and stable structure, is not formed. Meanwhile, if the heating temperature exceeds the upper limit, the specific surface area decreases, and catalytic performance is significantly deteriorated. The heating temperature is preferably in a temperature range of 800 to 1000 °C from the viewpoint of stabilizing the crystal phase of the shell material. In addition, a heating time for calcination cannot be generally specified because it depends on the heating temperature. However, the heating time is preferably 3 to 50 hours. Furthermore, a calcination atmosphere is not particularly limited and is preferably an air atmosphere or an oxidizing atmosphere.

[0063] In addition, grinding is not particularly limited, and in particular, either a dry grinding method or a wet grinding method can be used as the grinding method. Devices for grinding include a mortar, a ball mill, a mixer, and the like. When dry grinding is used, dry grinding can be performed using a mortar. Alternatively, a grinding and mixing device such as a ball mill, an agitator ball mill, or a planetary ball mill can be used. When wet grinding is used, a solvent is used as an aid for grinding, and examples include water, alcohols, and the like.Note that it is preferable to use a mortar, a mixer, or the like to perform the grinding, and a grinding condition is preferably such that the grinding is performed to an extent that the powder can pass a sieve having a predetermined diameter of the powder (about 100 nm to 100 μm). (Second coating step)

[0064] Subsequently, the prepared solution is brought into contact with the obtained core-shell powder to obtain the core-shell powder, which additionally supports the prepared solution in an amount that, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth zirconium oxide-based composite oxide constituting a part of the shell, based on 100 parts by mass of the oxygen storage / release material constituting the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding (second coating step).

[0065] A method for bringing the solution into contact with the obtained core-shell powder is not particularly limited, and it is possible to use, as appropriate, a known method by which the solution can be supported on the powder by adsorption, such as a method in which the powder is impregnated with the solution, a method in which the solution is supported on the powder by adsorption, a method in which the solution is impregnated with the powder, or the like. Methods that are the same as the contact methods described for the first coating step can be used.

[0066] In addition, a method for bringing the solution into contact with the powder of at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina is not particularly limited, and a known method may be employed as appropriate, such as a method in which the powder is impregnated with the solution, a method in which the solution is supported on the powder by adsorption, or the like.

[0067] When the solution is brought into contact with the core-shell powder, it is also necessary to support the prepared solution in an amount that, after calcination into an oxide, yields 1 to 8 mass parts of the rare earth zirconium oxide composite oxide constituting part of the shell, based on 100 mass parts of the oxygen storage / release material constituting the core. If the amount of the supported solution is less than the lower limit, it is difficult to exhibit sufficient catalytic activity. However, if the amount of the supported solution exceeds the upper limit, the solution will be unevenly supported or the composition will become uneven, thus reducing the catalytic activity.It should be noted that, from the viewpoint of supporting a solution having a uniform support density, the amount of the supported solution is preferably an amount that, after calcination into an oxide, gives 2 to 6 mass parts, and further preferably an amount that, after calcination into an oxide, gives 4 to 6 mass parts of the rare earth-zirconium oxide composite oxide constituting a part of the shell, based on 100 mass parts of the oxygen storage / release material constituting the core.

[0068] In addition, a heating condition for calcination must be in a temperature range of 600 to 1100 °C. If the heating temperature for calcination is lower than the lower limit, a pyrochlore phase, which is a desired stable structure, is not formed. Meanwhile, if the heating temperature exceeds the upper limit, the specific surface area decreases, and catalytic performance is significantly deteriorated. The heating temperature is preferably in a temperature range of 800 to 1000 °C from the viewpoint of stabilizing the crystal phase of the shell. In addition, a heating time for calcination cannot be generally specified because it depends on the heating temperature. However, the heating time is preferably 3 to 50 hours. Furthermore, a calcination atmosphere is not particularly limited and is preferably an air atmosphere or at least an oxidizing atmosphere.

[0069] In addition, the grinding is not particularly limited, and the method, conditions, and the like for the grinding are the same as those described for the first coating step.

[0070] Furthermore, with respect to the second coating step according to the method for producing a core-shell of the present invention, the core-shell support is obtained by performing this second coating step until an amount of the rare earth-zirconium oxide-based composite oxide forming the shell after calcination into the oxide reaches 4 to 24 parts by mass relative to 100 parts by mass of the oxygen storage / release material forming the core. It should be noted that the second coating step is preferably performed once or twice. If so, a surface layer enriched in the rare earth element and zirconium can be more uniformly deposited on the core surface, so that the pyrochlore structure (R 1-x Ce x )2Zr2O 7+x formed in the rare earth zirconium oxide composite oxide forming the shell can be further stabilized.

[0071] The method for producing a core-shell carrier of the present invention comprises the first coating step and the second coating step.

[0072] Thus, in the shell-forming process, the solution containing a rare earth element salt and a zirconium salt is supported in a low thickness by impregnation or adsorption on the powder of at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions or on the core-shell powder several times in a divided manner. In addition, each time the support by impregnation or adsorption is performed, high-temperature calcination and milling are carried out. Thus, a surface layer enriched in the rare earth element and zirconium can be uniformly deposited on the surface of the core made of the OSC material, and a Ce-poor pyrochlore structure (R 1-x Ce x )2Zr2O 7+xcan be formed and stabilized in the rare earth zirconium oxide-based composite oxide, which serves as the shell. Here, the Ce-poor pyrochlore structure (R 1-x Ce x )2Zr2O 7+x formed in such a way that the high-temperature calcination causes the Ce in the core, which is made of the OSC material, to be partially dissolved as a solid in the shell. [Process for producing the catalyst for exhaust gas purification]

[0073] Next, a method for producing an exhaust gas purification catalyst of the present invention will be described. The method for producing an exhaust gas purification catalyst of the present invention is a method for producing the above-described first exhaust gas purification catalyst of the present invention, which comprises: a solution preparation step for preparing a solution containing a rare earth element salt and a zirconium salt; a first coating step of bringing the prepared solution into contact with a powder of at least one oxygen storage / release material selected from the group consisting of ceria-zirconia-based solid solutions doped with alumina to obtain a core-shell powder supporting the prepared solution in an amount that, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth-zirconia-based composite oxide constituting a part of the shell, based on 100 parts by mass of the oxygen storage / release material constituting the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding; a second coating step of bringing the prepared solution into contact with the obtained core-shell powder to obtain a core-shell powder which additionally supports the prepared solution in an amount which, after calcination into an oxide, results in an amount of 1 to 8 parts by mass of the rare earth zirconium oxide-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding, wherein the core-shell support is obtained by carrying out the second coating step until an amount of the shell-forming composite oxide based on rare earth zirconium oxide after calcination into the oxide reaches 4 to 24 parts by mass based on 100 parts by mass of the core-forming oxygen storage / release material, and then the catalyst for exhaust gas purification is obtained by bringing a precious metal salt solution into contact with the core-shell carrier.

[0074] In the method for producing a catalyst for exhaust gas purification of the present invention, the solution preparation step, the first coating step, and the second coating step are the same as the solution preparation step, the first coating step, and the second coating step described for the method for producing a core-shell carrier.

[0075] Next, the exhaust gas purification catalyst is obtained by bringing a noble metal salt solution into contact with the core-shell support (catalyst preparation step). A specific method for bringing the noble metal salt solution into contact with the core-shell support in this catalyst preparation step is not particularly limited, and a method is preferably used in which, for example, the core-shell support is immersed in a solution obtained by dissolving a salt (nitrate, chloride, acetate, or the like) of the noble metal or a complex compound of the noble metal in a solvent such as water or alcohol, and the core-shell support is calcined and ground after removing the solvent.

[0076] It should be noted that in the catalyst preparation step, drying conditions for solvent removal are preferably about 180 minutes or less at 150 to 200°C, whereas calcination conditions are preferably about 3 to 5 hours at 300 to 400°C in an oxidizing atmosphere (e.g., air). Furthermore, such a noble metal support step can be repeated until a desired amount of supported noble metal is achieved.

[0077] In addition, the noble metal supported in the process for producing an exhaust gas purification catalyst of the present invention may preferably be platinum, rhodium or palladium, and from the viewpoint of obtaining an exhaust gas purification catalyst having both sufficiently high oxygen storage / release capacity (OSC) and sufficiently high NOx removal activity, particularly preferably Rh. [Exhaust gas purification process]

[0078] Next, an exhaust gas purification method of the present invention will be described. The exhaust gas purification method of the present invention is a method that comprises purifying an exhaust gas emitted from an internal combustion engine by bringing the exhaust gas into contact with the above-described exhaust gas purification catalyst of the present invention.

[0079] In the exhaust gas purification method of the present invention, a method for bringing the exhaust gas into contact with the exhaust gas purification catalyst of the present invention is not particularly limited, and any known method can be used as appropriate. For example, a method can be used in which the exhaust gas from an internal combustion engine is brought into contact with the exhaust gas purification catalyst according to the present invention by disposing the exhaust gas purification catalyst in an exhaust pipe through which the exhaust gas emitted from the internal combustion engine flows.

[0080] It should be noted that the exhaust gas purification catalyst of the present invention described above, which is used in the exhaust gas purification method of the present invention, exhibits both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity. Thus, the exhaust gas purification catalyst of the present invention can exhibit both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity.When an exhaust gas from, for example, an internal combustion engine is brought into contact with the exhaust gas purifying catalyst of the present invention, the exhaust gas purifying catalyst of the present invention can exhibit both a sufficiently high oxygen storage / release capacity (OSC) and a sufficiently high NOx removal activity, so that harmful gases such as NOx contained in the exhaust gas can be sufficiently removed. From such viewpoints, the exhaust gas purifying method of the present invention can be suitably used as a method for removing, for example, harmful components such as harmful gases (hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (NOx)) contained in an exhaust gas emitted from an internal combustion engine in an automobile, etc. [Examples]

[0081] The present invention will be described more specifically below based on Inventive Examples 5 and 6, Non-Inventive Examples 1 to 4, and Non-Inventive Comparative Examples; however, the present invention is not limited to the following examples. (Non-inventive example 1)

[0082] First, 10 g of a powder of a solid solution based on cerium oxide-zirconia with a composition (in mass percent) of CeO2:ZrO2:La2O3:Y2O3 = 30:60:5:5, an average particle diameter of 5 µm and a specific surface area of ​​70 m 2 / g. A solution was then prepared by dissolving 0.7×10 -3 mol of zirconyl oxynitrate (produced by Wako Pure Chemical Industries, Ltd.) and 0.7×10 -3mol of lanthanum nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 100 ml of ion-exchanged water (solution preparation step).

[0083] Next, 10 g of the ceria-zirconia solid solution powder was added to the prepared solution, followed by stirring for 15 minutes. Further, the mixture was heated with stirring to impregnate the ceria-zirconia solid solution powder with the solution (impregnation by impregnation). This impregnated powder was then evaporated to dryness to achieve coagulation (evaporation to dryness). Subsequently, the obtained coagulation was calcined in air at a temperature condition of 900 °C for 5 hours and then ground into a powder using a mortar for 30 minutes or more to obtain a core-shell powder (first coating step).

[0084] Subsequently, a core-shell support was obtained by performing a single series of processes in which the solution was supported on the obtained core-shell powder by impregnation in the same manner as in the first coating step described above, and then the impregnated powder was evaporated to dryness, followed by calcination and grinding (second coating step).

[0085] Next, the obtained core-shell support was impregnated with 0.1 L of a rhodium nitrate solution containing 0.015 g of rhodium (Rh) as the metal. This impregnated support was then evaporated to dryness by heating it with stirring in air at a temperature condition of 200 °C for 120 minutes to achieve coagulation (evaporation to dryness). Subsequently, a powdered exhaust gas purification catalyst was obtained by calcination in air at a temperature condition of 300 °C for 5 hours. Note that the amount of rhodium supported in the obtained exhaust gas purification catalyst was 0.15% by mass based on 100% of the core-shell support. (Non-inventive example 2)

[0086] A core-shell support was obtained in the same manner as in Example 1, except that the dissolved amounts of zirconyl oxynitrate and lanthanum nitrate were each 2.1 × 10-3 mol were changed. Furthermore, a powdered exhaust gas purification catalyst was obtained by supporting Rh as the noble metal on the obtained core-shell support in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained exhaust gas purification catalyst was 0.15 mass % based on 100 mass % of the core-shell support. (Non-inventive example 3)

[0087] A core-shell support was obtained in the same manner as in Example 1, except that the second coating step (another series of processes of supporting the solution by soaking, evaporation to dryness, calcination and grinding) was carried out again on the obtained core-shell powder, with the amounts of dissolved zirconyl oxynitrate and lanthanum nitrate each being 2.1 × 10 -3mol (the second coating step was performed twice in total). Furthermore, a powdered exhaust gas purification catalyst was obtained by supporting Rh as the noble metal on the obtained core-shell support in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained exhaust gas purification catalyst was 0.15% by mass based on 100% by mass of the core-shell support. (Non-inventive example 4)

[0088] A core-shell support was obtained in the same manner as in Example 3, except that neodymium nitrate (dissolved amount: 2.1 × 10 -3mol) was added to the prepared solution. Furthermore, a powdered exhaust gas purification catalyst was obtained by supporting Rh as the noble metal on the obtained core-shell support in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained exhaust gas purification catalyst was 0.15 mass % based on 100 mass % of the core-shell support. (Inventive Example 5)

[0089] A core-shell support was obtained in the same manner as in Example 1, except that a powder of an alumina-doped ceria-zirconia-based solid solution with a composition of (in mass %) Al2O3:CeO2:ZrO2:La2O3:Y2O3:Nd2O3 = 30:20:44:2:2:2, an average particle diameter of 8 µm and a specific surface area of ​​70 m 2 / g was used instead of the powder of the cerium oxide-zirconia-based solid solution, and the amounts of dissolved zirconyl oxynitrate and lanthanum nitrate were each set to 2.1× 10 -3 mol. Furthermore, a powdered exhaust gas purification catalyst was obtained by supporting Rh as the noble metal on the obtained core-shell support in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained exhaust gas purification catalyst was 0.15% by mass based on 100% by mass of the core-shell support. (Inventive Example 6)

[0090] A core-shell powder was obtained in the same manner as in Example 1, except that a powder of an alumina-doped ceria-zirconia-based solid solution with a composition of (in mass %) Al2O3:CeO2:ZrO2:La2O3:Y2O3:Nd2O3 = 30:20:44:2:2:2, an average particle diameter of 8 µm and a specific surface area of ​​70 m 2 / g was used instead of the powder of the solid solution based on cerium oxide-zirconium oxide, that the amounts of dissolved zirconyl oxynitrate and lanthanum nitrate each to 2.1 × 10 -3mol were changed, and further, the second coating step (a different series of processes of supporting the solution by soaking, evaporation to dryness, calcination, and milling) was performed again on the obtained core-shell powder (the second coating step was performed twice in total). Furthermore, a powdered exhaust gas purification catalyst was obtained by supporting Rh as the noble metal on the obtained core-shell powder in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained exhaust gas purification catalyst was 0.15 mass% based on 100 mass% of the core-shell support. (Comparison example 1)

[0091] As a catalyst support for comparison, 10 g of a powder of a solid solution based on ceria-zirconia (with a composition (in mass percent) of CeO2:ZrO2:La2O3:Y2O3 = 30:60:5:5, an average particle diameter of 8 µm and a specific surface area of ​​60 m 2 / g) was used. Next, a powdered catalyst for comparison was obtained by supporting Rh as the noble metal on 10 g of the powder of the catalyst support for comparison in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained powder of the catalyst for comparison was 0.15 mass % based on 100 mass % of the catalyst support for comparison. (Comparison example 2)

[0092] As a catalyst support for comparison, 10 g of a powder of alumina-doped ceria-zirconia-based solid solution was used (with a composition (in mass percent) of Al2O3:CeO2:ZrO2:La2O3:Y2O3:Nd2O3 = 30:20:44:2:2:2, an average particle diameter of 8 µm and a specific surface area of ​​70 m 2 / g). Next, a powdered catalyst for comparison was obtained by supporting Rh as the noble metal on 10 g of the powder of the catalyst support for comparison in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained powder of the catalyst for comparison was 0.15 mass % based on 100 mass % of the catalyst support for comparison. (Comparison example 3)

[0093] First, 10 g of a cerium oxide-zirconia solid solution powder was prepared (with a composition (in mass percent) of CeO2:ZrO2:La2O3:Y2O3 = 30:60:5:5, an average particle diameter of 8 µm and a specific surface area of ​​60 m 2 / g). A solution was then prepared by dissolving 0.7×10 -3 mol of zirconyl oxynitrate dihydrate (produced by Wako Pure Chemical Industries, Ltd.) and 0.7×10 -3 mol of lanthanum nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 100 ml of ion-exchanged water.

[0094] Next, 10 g of the ceria-zirconia-based solid solution powder was added to the prepared solution, followed by stirring for 15 minutes. Further, the mixture was heated with stirring to impregnate the ceria-zirconia-based solid solution powder with the solution (support by impregnation). This impregnated powder was then evaporated to dryness to achieve coagulation (evaporation to dryness). Subsequently, the obtained coagulation was calcined in air at a temperature condition of 900 °C for 5 hours and then ground into a powder using a mortar for 30 minutes or more to obtain a catalyst support for comparison.

[0095] Subsequently, a powdered catalyst for comparison was obtained by supporting Rh as the noble metal on 10 g of the powder of the catalyst support for comparison in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained catalyst for comparison was 0.15 mass % based on 100 mass % of the catalyst support for comparison. (Comparison example 4)

[0096] First, 10 g of a cerium oxide-zirconia solid solution powder was prepared (with a composition (in mass percent) of CeO2:ZrO2:La2O3:Y2O3 = 30:60:5:5, an average particle diameter of 8 µm and a specific surface area of ​​60 m 2 / g). A solution was then prepared by dissolving 8.75 × 10 -3 mol of zirconyl oxynitrate dihydrate (produced by Wako Pure Chemical Industries, Ltd.) and 8.75 × 10 -3mol of lanthanum nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 100 ml of ion-exchanged water.

[0097] Next, 10 g of the ceria-zirconia-based solid solution powder was added to the prepared solution, followed by stirring for 15 minutes. Further, the mixture was heated with stirring to impregnate the ceria-zirconia-based solid solution powder with the solution (support by impregnation). This impregnated powder was then evaporated to dryness to achieve coagulation (evaporation to dryness). Subsequently, the obtained coagulation was calcined in air at a temperature condition of 900 °C for 5 hours and then ground into a powder using a mortar for 30 minutes or more to obtain a catalyst support for comparison.

[0098] Subsequently, a powdered catalyst for comparison was obtained by supporting Rh as the noble metal on 10 g of the powder of the catalyst support for comparison in the same manner as in Example 1. Note that the amount of rhodium supported in the obtained catalyst for comparison was 0.15 mass % based on 100 mass % of the catalyst support for comparison. [X-ray diffraction (XRD) measurement]

[0099] The average crystal diameter (average primary particle diameter) of the shell (rare earth-zirconium oxide composite oxide) of each catalyst obtained in Examples 1 to 6 and Comparative Examples 3 and 4 was measured as follows.

[0100] First, using each of the catalysts obtained in Examples 1 to 6 and Comparative Examples 3 and 4 as a measurement sample, an X-ray diffraction (XRD) pattern of the shell (rare earth-zirconium oxide composite oxide) of the catalyst was obtained by measurement using a powder X-ray diffraction apparatus (a general-purpose horizontal sample holder X-ray diffractometer produced by Rigaku Corporation under the trade name “Ultima IV”) under the conditions of a scanning pitch of 0.02, a divergence slit of 8 degrees, a scattering slit of 8 degrees, a receiving slit of 10 mm, CuKα radiation (λ = 0.15418 nm), 40 kV, 40 mA, and a scanning speed of 10 degrees per minute.For the shell for which the XRD pattern was thus obtained, the mean crystal diameter (mean primary particle diameter) attributable to the rare earth zirconia composite oxide was determined by calculation based on the diffraction line width of a peak (2θ= 10 to 80°) using the Scherrer equation:. D=0.89×λ / βcosθ, where D represents the crystal diameter, λ represents the wavelength of the X-ray beam used, β represents the diffraction linewidth of the XRD sample, and θ represents the diffraction angle. Table 1 shows the results obtained.

[0101] As is clear from the average crystal diameter of the rare earth-based zirconia composite oxide of each of Examples 1 to 6 and Comparative Examples 3 and 4 at an initial stage shown in Table 1, it was found that the average crystal diameter of the rare earth-based zirconia composite oxide of each of Examples 1 to 6 was in the range of 3 to 9 nm. [Table 1] Shell (composite oxide based on rare earth zirconium oxide) Evaluation of the stoichiometric three-way activity Evaluation of transient NOx removal activity Evaluation of OSC activity Average crystal diameter [nm] x in the composition formula Temperature for 50% NOx removal (NOx_T50) [°C] Transient NOx removal ratio [%] OSC rate [µmol-O2 / g / s] Example 1 4 0,80 343 82 24 Example 2 7 0,69 338 88 23 Example 3 8 0,58 339 89 23 Example 4 8 0,58 340 85 22 Example 5 6 0,43 316 90,9 23 Example 6 9 0,37 325 91,6 24 See Example 1 - 0,90 357 71 24 See Example 2 - 0,90 332 85,9 23,5 See Example 3 2 0,88 356 78 24 See Example 4 10 0,48 347 82 18

[0102] Next, the composition (composition formula: (R 1-x Ce x )2Zr2O 7+x, where R represents a rare earth element which is at least one element selected from the group consisting of La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y, and x represents a number from 0.0 to 0.8) of the shell (rare earth-zirconium oxide composite oxide) of each of the catalysts obtained in Examples 1 to 6 and Comparative Examples 3 and 4, and x in the composition formula is determined as follows. Specifically, assuming a crystal lattice constant that changes linearly between the crystal lattice constant calculated from the peak position of R2Zr2O7 and the crystal lattice constant calculated from the peak position of Ce2Zr2O8, the amount of Ce in the shell material, i.e., the value of x, was determined from the crystal lattice constant calculated from the peak position of the shell material. Table 1 shows the obtained results.

[0103] In addition, the presence or absence of the pyrochlore phase was determined based on the presence or absence of a peak at approximately 2θ = 14.2° (degrees) after continuous operation. [High-temperature continuous treatment]

[0104] Each of the catalyst powders obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was subjected to powder compression by cold isostatic pressing (CIP) using an isostatic press (manufactured by NIKKISO CO. Ltd. under the trade name “CK4-22-60”) at a pressure (pressing pressure) of 1000 kgf / cm 2 for 1 minute, followed by crushing and size selection to obtain pellets ranging in size from 0.5 to 1.0 mm. Thus, a pellet catalyst sample was obtained for an evaluation test (pellet-shaped catalyst for exhaust gas purification).

[0105] Next, the obtained pellet catalyst sample (1.5 g) was placed in a normal-pressure flow-through fixed-bed reactor. Subsequently, a model gas treatment was performed in which a lean (L) gas and a rich (R) gas with the gas compositions shown in Table 2 were alternately passed for 5 minutes each and for a total of 5 hours under a temperature condition of 1100 °C at a flow rate of 10 L (liters) / minute. Thus, a high-temperature continuous treatment (continuous test) was performed. [Table 2] O2(volume%) H2(volume%) CO2 (volume %) N2 Lean (L) 1,0 - 10,0 rest Fat (R) - 2,0 10,0 rest [Evaluation test for stoichiometric three-way activity]

[0106] The 50% NOx removal temperature (NOx_T50) of each of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was measured by conducting a stoichiometric three-way activity evaluation test on the pellet catalyst sample subjected to the high-temperature endurance treatment using a flow reactor and an exhaust gas analyzer as follows.

[0107] Specifically, first, the pellet catalyst sample subjected to the high-temperature continuous treatment was placed in a reaction chamber (internal space: diameter 1.7 cm and length 9.5 cm) of a normal-pressure flow-through fixed-bed reactor. Note that the amount of the catalyst sample of each of Examples 1 to 4 and Comparative Examples 1, 3, and 4 was 0.5 g, and the catalyst sample was filled into the reaction chamber. Meanwhile, the amount of the catalyst sample of each of Examples 5 to 6 and Comparative Example 2 was 0.25 g. Furthermore, 0.25 g of silica sand was added to 0.25 g of the catalyst sample of each of Examples 5 to 6 and Comparative Example 2, followed by mixing. Then, the mixture was filled into the reaction chamber.

[0108] Next, a model exhaust gas consisting of three harmful gases with the gas composition shown in Table 3 was supplied under a temperature condition of 600 °C at a flow rate of 10 L / minute for 6 minutes (pretreatment). Afterward, the temperature of each sample was cooled to 100 °C. While the model exhaust gas was supplied at a flow rate of 10 L / minute, the sample was then heated from 100 °C to 600 °C at a temperature rise rate of 6 °C / minute. The temperature (50% NOx removal temperature, °C, referred to as "NOx_T50") at which the NOx removal ratio in the supplied model exhaust gas reached 50% was measured. [Table 3] CO2 (volume %) O2(volume%) CO (volume %) NO(ppm) C3H6(ppmCC*l)) H2(volume%) H2O (volume %) N2 Model gas 10,0 0,646 0,7 1200 1600 0,233 10,0 rest *1: ppmC (volume ratio of carbon)

[0109] Table 1 shows the results obtained. In addition, the Fig.Figure 1 is a graph showing the 50% NOx removal temperatures (NOx_T50) of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 2. [Evaluation test for transient NOx removal activity]

[0110] The transient NOx removal ratio of each of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was measured by conducting a transient NOx removal activity evaluation test on the pellet catalyst sample subjected to the high-temperature endurance treatment using a flow reactor and an exhaust gas analyzer as follows.

[0111] Specifically, first, the pellet catalyst sample subjected to the high-temperature continuous treatment was placed in a reaction chamber (internal space: diameter 1.7 cm and length 9.5 cm) of a normal-pressure flow-through fixed-bed reactor. Note that the amount of the catalyst sample in each of Examples 1 to 4 and Comparative Examples 1, 3, and 4 was 0.5 g, and the catalyst sample was filled into the reaction chamber. Meanwhile, the amount of the catalyst sample in each of Examples 5 and 6 and Comparative Example 2 was 0.25 g. Furthermore, 0.25 g of silica sand was added to 0.25 g of the catalyst sample in each of Examples 5 and 6 and Comparative Example 2, followed by mixing. Then, the mixture was filled into the reaction chamber.

[0112] Next, under a temperature condition of 500 °C, a lean model exhaust gas with the gas composition shown in Table 4 was passed at a flow rate of 10 L (liters) / minute for 180 seconds. Then, the gas composition was switched to that of a rich model exhaust gas with the gas composition shown in Table 4, and this rich model exhaust gas was passed at a flow rate of 10 L (liters) / minute for 180 seconds. This cycle was repeated several times. Afterward, the NOx removal ratio (transient NOx removal ratio, %) was measured 180 seconds after switching the gas composition from lean to rich. [Table 4] CO2 (volume %) O2(volume%) CO (volume %) NO(ppm) C3H6(ppmC (*1) ) H2O (volume %) N2 Lean (L) 10,0 0,8 0,65 1500 3000 5,0 rest Fat (R) 10,0 0,0 0,65 1500 3000 5,0 rest *1: ppmC (volume ratio of carbon)

[0113] Table 1 shows the results obtained. In addition, the Fig.2 is a graph showing the transient NOx removal ratios (%) of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 4. [Test for measuring the amount of OSC (oxygen storage / release): OSC Activity Evaluation Test]

[0114] The OSC rate of each of the pellet catalyst samples obtained in Examples 1 to 6 and Comparative Examples 1 to 4 and subjected to the high-temperature endurance treatment was measured by conducting an OSC activity evaluation test using a flow reactor and an analyzer as follows.

[0115] Specifically, first, the pellet catalyst sample subjected to the high-temperature continuous treatment was placed in a reaction chamber (internal space: diameter 1.7 cm and length 9.5 cm) of a normal-pressure flow-through fixed-bed reactor. Note that the amount of the catalyst sample in each of Examples 1 to 4 and Comparative Examples 1, 3, and 4 was 0.5 g, and the catalyst sample was filled into the reaction chamber. Meanwhile, the amount of the catalyst sample in each of Examples 5 and 6 and Comparative Example 2 was 0.25 g. Furthermore, 0.25 g of silica sand was added to 0.25 g of the catalyst sample in each of Examples 5 and 6 and Comparative Example 2, followed by mixing. Then, the mixture was filled into the reaction chamber.

[0116] Next, a rich gas (CO (2% volume) + N2 (the balance)) and a lean gas (O2 (1% volume) + N2 (the balance)) were alternately passed through the flow-type fixed-bed reactor under a temperature condition of 500 °C, switching from one to the other every three minutes. After switching to the rich gas, the amount of oxygen (O2) generated in the rich gas atmosphere was measured, and the oxygen (O2) generation rate, which was the amount of oxygen (O2) generated in 5 seconds after the introduction of the rich gas, was measured as the oxygen storage / release (OSC) rate (µmol / g / sec or µmol-O2 / g / s). Note that the gas flow rate was 10 L / min, and an analyzer produced by BEST INSTRUMENTS CO. Ltd. was used. under the trade name “Bex5900Csp”.

[0117] Table 1 shows the results obtained. In addition, the Fig.3 is a graph showing the OSC rates (µmol-O2 / g / s) of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 4.

[0118] Table 5 shows the structures of the core-shell supports and exhaust gas purification catalysts obtained in Examples 1 to 6 and the catalyst supports and comparative catalysts obtained in Comparative Examples 1 to 4. [Table 5] Catalyst structure core Peel Amount of supported shell [mass%] Precious metal Amount of supported precious metal [mass%] Example 1 CeO2-ZrO2-La2O3-Y2O3 (At 0,2 -What 0,8 )2Zr2O 7,8 4,0 Rh 0,15 Example 2 CeO2-ZrO2-La2O3-Y2O3 (At 0,31 -What 0,69 )2Zr2O 7,69 12,0 Rh 0,15 Example 3 CeO2-ZrO2-La2O3-Y2O3 (The 0,42 -CEO 0,58 )2Zr2O 7,58 18,0 Rh 0,15 Example 4 CeO2-ZrO2-La2O3-Y2O3 (At 0,42 -What 0,58 )2Zr2O 7,58 18,0 Rh 0,15 Example 5 Al2O3-CeO2-ZrO2-La2O3-Y2O3-Nd2O3 (At 0,57 -What 0,43 )2Zr2O 7,43 12,0 Rh 0,15 Example 6 Al2O3-CeO2-ZrO2-La2O3-Y2O3-Nd2O3 (At 0,63 -What 0,37 )2Zr2O 7,37 18,0 Rh 0,15 See Example 1 CeO2-ZrO2-La2O3-Y2O3 - - Rh 0,15 See Example 2 Al2O3-CeO2-ZrO2-La2O3-Y2O3-Nd2O3 - - Rh 0,15 See Example 3 CeO2-ZrO2-La2O3-Y2O3 (At 0.12 -What 0.88 )2ZF2O 7.88 2,0 Rh 0,15 See Example 4 CeO2-ZrO2-La2O3-Y2O3 (At 0.52 -What 0.48 )2Zr2O 7.48 25,0 Rh 0,15

[0119] As can be seen from a comparison of the results of Examples 1 to 6 with the results of Comparative Examples 1 to 4 shown in Table 1 and the Fig.1 to 3, it was found that the core-shell support and the exhaust gas purification catalyst of each of Examples 1 to 6 achieved both excellent NOx removal ratio and OSC (oxygen storage / release) performance. Accordingly, it is conceivable that each of the catalysts of Examples 1 to 6 was excellent in both NOx removal ratio and OSC (oxygen storage / release) performance because the catalyst comprised a core comprising a ceria-zirconia-based solid solution or an alumina-doped ceria-zirconia-based solid solution, and a shell comprising a rare earth-zirconia-based composite oxide represented by the composition formula (R 1-x Ce x )2Zr2O 7+x, where R represents a rare earth element and x represents a number from 0.0 to 0.8, and with which the outside of the core has been coated, wherein the rare earth-zirconium oxide composite oxide comprised crystal particles having a pyrochlore structure, and the average crystal diameter of the rare earth-zirconium oxide composite oxide was limited to the range of 3 to 9 nm. (Inventive Examples 7 to 9 and Non-inventive Comparative Examples 5 to 7) <1. Materials Used>[Material 1]

[0120] As aluminum oxide (Al2O3), a composite oxide containing 1% by mass of La2O3 and 99% by mass of Al2O3 was used (hereinafter also referred to as “Material 1”). [Material 2]

[0121] A composite oxide containing 30% by mass of Al2O3, 20% by mass of CeO2, 45% by mass of ZrO2, and 5% by mass of La2O3 (hereinafter also referred to as “Material 2”) was used as an alumina-doped solid solution (ACZL). [Material 3]

[0122] As a core-shell support (LZ-ACZL) of the present invention, a core-shell support obtained as described below (hereinafter also referred to as “Material 3”) was used.

[0123] First, 10 g of a powder (average particle diameter: 8 µm, specific surface area: 70 m 2 / g) of material 2. A solution was then prepared by dissolving 2.1 × 10 -3 mol of zirconyl oxynitrate (produced by Wako Pure Chemical Industries, Ltd.) and 2.1 × 10 -3mol of lanthanum nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 100 ml of ion-exchanged water (solution preparation step).

[0124] Next, 10 g of the powder was added to the prepared solution, followed by stirring for 15 minutes. Further, the mixture was heated with stirring to impregnate the powder with the solution (impregnation by impregnation). This impregnated powder was then evaporated to dryness to achieve coagulation (evaporation to dryness). Subsequently, the resulting coagulation was calcined in air at a temperature of 900 °C for 5 hours and then ground into a powder using a mortar for 30 minutes or more to obtain a core-shell powder (first coating step).

[0125] Subsequently, a core-shell support shown below was obtained by performing a single series of processes in which the prepared solution is supported on the obtained core-shell powder by impregnation and then the impregnated powder was evaporated to dryness, followed by calcination and grinding in the same manner as in the first coating step (second coating step) described above. Core: Al2O3-CeO2-ZrO2-La2O3 Shell (x = 0 in the composition formula): La2Zr2O7 Average crystal diameter of the shell: 6 nm Amount of supported shell: 12.0% by mass. [Material 4]

[0126] As an alumina-doped solid solution (AZL), a composite oxide containing 30 wt% Al2O3, 65 wt% ZrO2 and 5 wt% La2O3 was used (hereinafter also referred to as “Material 4”). [Material 5]

[0127] As a material of a rhodium catalyst, an aqueous rhodium nitrate solution (produced by Cataler Corporation) with a precious metal content of 2.75 mass % was used (hereinafter also referred to as the “Material 5”). [Material 6]

[0128] As a material of a palladium catalyst, an aqueous palladium nitrate solution (produced by Cataler Corporation) with a noble metal content of 8.8% by mass was used (hereinafter also referred to as the “Material 6”). [Substrates]

[0129] Cordierite honeycomb substrates 875 cc (600H / 3-9R-08) (produced by DENSO CORPORATION) were used as substrates. <2. Preparation of catalysts>[Comparative Example 5]

[0130] Double-layer catalyst with upper layer (Rh(0.10) / ACZL(110) + Al2O3(28)) and lower layer (Pd(0.69) / ACZL(45) + Al2O3(40)) (Formation of the lower layer)

[0131] First, a material in which palladium (Pd) was supported on the alumina-doped ceria-zirconia (ACZL) solid solution (Pd / ACZL, hereinafter referred to as "Material 7") was prepared by an impregnation method using Materials 2 and 6. Next, Material 7, Material 1, and an alumina-based binder (AS-200, manufactured by Nissan Chemical Industries Ltd.) were suspended in distilled water with stirring to obtain a slurry. The obtained slurry was then poured into the substrate. An unnecessary portion of the slurry was blown off with a fan. Through the processes or steps described above, the surfaces of the inner walls of the substrate were coated with the materials.Here, the preparation was carried out under conditions such that the resulting substrate coated with the lower layer contained 0.69 g / L palladium, 40 g / L of Material 1, and 45 g / L of Material 2 per liter of the substrate's capacity. The slurry-coated substrate was then allowed to stand in a dryer set at 120 °C for 2 hours to allow the water in the slurry to evaporate. Furthermore, the substrate was allowed to stand in an electric furnace set at 500 °C for 2 hours to obtain a substrate with a palladium-containing catalyst layer. (Formation of the upper layer)

[0132] Next, a material in which rhodium (Rh) was supported on the alumina-doped ceria-zirconia (ACZL)-based solid solution (Rh / ACZL, hereinafter also referred to as "Material 8") was prepared by an impregnation method using Materials 2 and 5. Next, Material 8, Material 1, and the alumina-based binder were suspended in distilled water with stirring to obtain a slurry. The obtained slurry was then poured into the substrate with the palladium-containing catalyst layer. An unnecessary portion of the slurry was blown off with a fan. Through the above-described procedures, the materials were coated onto the inner wall surfaces of the substrate.Here, the preparation was carried out under conditions such that the resulting substrate coated with the upper layer contained 0.10 g / L of rhodium, 28 g / L of Material 1, and 110 g / L of Material 2 per liter of the substrate's capacity. The slurry-coated substrate was then allowed to stand in a dryer set at 120 °C for 2 hours to allow the water in the slurry to evaporate. Furthermore, the substrate was allowed to stand in an electric furnace set at 500 °C for 2 hours. Thus, a double-layer catalyst was obtained, which had the rhodium-containing catalyst layer as the upper layer and the palladium-containing catalyst layer as the lower layer. [Comparison example 6]

[0133] Double-layer catalyst with upper layer (Rh(0.10) / AZL(55) + ACZL(55) + Al2O3(28)) and lower layer (Pd(0.69) / ACZL(45) + Al2O3(40))

[0134] First, a material in which rhodium (Rh) was supported on the alumina-doped zirconia-based solid solution (AZL) (Rh / AZL, hereinafter also referred to as "Material 9") was prepared by an impregnation method using Materials 4 and 5. Next, a double-layer catalyst having a rhodium-containing catalyst layer as the upper layer and a palladium-containing catalyst layer as the lower layer was obtained by the same procedure as in Comparative Example 5, except that a slurry containing Material 9, Material 2, Material 1, and the alumina-based binder was used in the upper layer formation step.Here, the preparation was carried out under such conditions that the resulting substrate coated with the top layer contained 0.10 g / L rhodium, 28 g / L material 1, 55 g / L material 2 and 55 g / L material 4 per liter of the capacity of the substrate. [Comparison Example 7]

[0135] Double-layer catalyst with upper layer (Rh(0.05) / AZL(55) + Rh(0.05) / ACZL(55) + Al2O3(28)) and lower layer (Pd(0.69) / ACZL(45) + Al2O3(40))

[0136] A double-layer catalyst was obtained with a rhodium-containing catalyst layer as the upper layer and a palladium-containing catalyst layer as the lower layer by the same procedure as in Comparative Example 5, except that a slurry containing Material 9, Material 8, Material 1, and the alumina-based binder was used in the upper layer formation step. Here, the preparation was carried out under conditions such that the resulting upper-layer-coated substrate contained 0.10 g / L of rhodium, 28 g / L of Material 1, 55 g / L of Material 2, and 55 g / L of Material 4 per liter of the substrate capacity. [Example 7]

[0137] Double-layer catalyst with upper layer (Rh(0.10) / LZ-ACZL(110) + Al2O3(28)) and lower layer (Pd(0.69) / ACZL(45) + Al2O3(40))

[0138] First, a material in which rhodium (Rh) was supported on the core-shell support of the present invention (LZ-ACZL) (Rh / LZ-ACZL, hereinafter also referred to as "Material 10") was prepared by an impregnation method using Materials 3 and 5. Next, a double-layer catalyst having a rhodium-containing catalyst layer as the upper layer and a palladium-containing catalyst layer as the lower layer was obtained by the same procedure as in Comparative Example 5, except that a slurry containing Material 10, Material 1, and the alumina-based binder was used in the upper layer formation step. Here, the preparation was carried out under conditions such that the resulting upper-layer-coated substrate contained 0.10 g / L of rhodium, 28 g / L of Material 1, and 110 g / L of Material 3 per liter of the substrate capacity. [Example 8]

[0139] Double-layer catalyst with upper layer (Rh(0.10) / AZL(55) + LZ-ACZL(55) + Al2O3(28)) and lower layer (Pd(0.69) / ACZL(45) + Al2O3(40))

[0140] A double-layer catalyst was obtained with a rhodium-containing catalyst layer as the upper layer and a palladium-containing catalyst layer as the lower layer by the same procedure as in Comparative Example 5, except that a slurry containing Material 9, Material 3, Material 1, and the alumina-based binder was used in the upper layer formation step. Here, the preparation was carried out under conditions such that the resulting upper-layer-coated substrate contained 0.10 g / L of rhodium, 28 g / L of Material 1, 55 g / L of Material 3, and 55 g / L of Material 4 per liter of the substrate capacity. [Example 9]

[0141] Double-layer catalyst with upper layer (Rh(0.05) / AZL(55) + Rh(0.05) / LZ-ACZL(55) + Al2O3(28)) and lower layer (Pd(0.69) / ACZL(45) + Al2O3(40))

[0142] A double-layer catalyst was obtained with a rhodium-containing catalyst layer as the upper layer and a palladium-containing catalyst layer as the lower layer by the same procedure as in Comparative Example 5, except that a slurry containing Material 9, Material 10, Material 1, and the alumina-based binder was used in the upper layer formation step. Here, the preparation was carried out under conditions such that the resulting upper-layer-coated substrate contained 0.10 g / L of rhodium, 28 g / L of Material 1, 55 g / L of Material 3, and 55 g / L of Material 4 per liter of the substrate capacity. <3. Method for evaluating catalysts>[Continuous treatment]

[0143] Using a gasoline internal combustion engine (1UR-FE, manufactured by Toyota Motor Corporation), accelerated deterioration treatment was performed on the catalysts of Examples 7 to 9 and Comparative Examples 5 to 7 under conditions of 1000 °C (catalyst bed temperature) and for 25 hours. During this time, the treatment was repeatedly performed in a constant cycle by adjusting the throttle opening angle and engine load: a rich condition, a stoichiometric condition, and a lean condition. This changed the exhaust gas composition and accelerated catalyst deterioration. [OSC Evaluation Test]

[0144] Using a gasoline internal combustion engine (2AZ-FE, manufactured by Toyota Motor Corporation), the oxygen storage characteristics of the catalysts from Examples 7 to 9 and Comparative Examples 5 to 7 were evaluated (after accelerated deterioration treatment). An air-fuel ratio (A / F) was controlled to a target A / F of 14.1 or 15.1. The excess or deficiency of oxygen was calculated according to the following expression based on a difference (ΔA / F) between the theoretical air-fuel ratio and an A / F sensor output at the stoichiometric point. The maximum oxygen storage was evaluated as OSC. OSC[g]=0.23×ΔA / F×fuel injection quantity. [Evaluation test for stationary NOx removal performance]

[0145] Using a gasoline internal combustion engine (2AZ-FE, manufactured by Toyota Motor Corporation), the steady-state NOx removal performance of the catalysts from Examples 7 to 9 and Comparative Examples 5 to 7 (after accelerated deterioration treatment) was evaluated. An air-fuel ratio (A / F) was controlled to a target A / F of 14.1, and the NOx emission in the exhaust gas passed through each catalyst was determined under a condition of 600 °C. <4. Evaluation results of the catalysts>

[0146] The maximum oxygen storage capacity (OSC) and NOx emission of each of the catalysts from Examples 7 to 9 and Comparative Examples 5 to 7 (after accelerated deterioration treatment) were evaluated using the procedures described above. Table 6 and the Fig. 4 shows the results. It should be noted that in the Fig.4 the bar shows the maximum oxygen storage (OSC) and the line shows the NOx emission. [Table 6] Maximum oxygen storage (OSC) [g] NOx emissions [ppm] See Example 5 0,30 500 See Example 6 0,15 358 See Example 7 0,24 412 Example 7 0,30 250 Example 8 0,21 200 Example 9 0,25 215

[0147] As shown in Table 6 and the Fig.As shown in Figure 4, because the noble metal was directly supported on the OSC material in the coating layer (upper layer) of the catalyst of Comparative Example 5, the catalyst of Comparative Example 5 achieved high OSC performance, but NOx emission was very high. Meanwhile, in the catalyst of Comparative Example 6, the noble metal was supported on the other material and coexisted with the OSC material in the coating layer (upper layer). The catalyst of Comparative Example 6 was improved in NOx emission, but the OSC performance was greatly deteriorated. In addition, in the catalyst of Comparative Example 7, half of the noble metal was directly supported on the OSC material, and the other half of the noble metal was supported on the other material.The performances of the catalyst of Comparative Example 7 were ranked between those of the catalyst of Comparative Example 5 and those of the catalyst of Comparative Example 6, and the two performances were not improved.

[0148] The catalysts of Examples 7 to 9 each used the core-shell support of the present invention, LZ-ACZL, which was a surface-modified OSC material. Therefore, it was found that the catalyst of Example 7 was improved in NOx removal performance and also achieved a high level of OSC performance even though the noble metal was directly supported on the core-shell support of the present invention in the coating layer (upper layer). In addition, it was found that the catalyst of Example 8 was improved in NOx removal performance and also achieved a high level of OSC performance even though the noble metal was supported on the other material and coexisted with the core-shell support of the present invention in the coating layer (upper layer).Furthermore, it was found that the catalyst of Example 9 was improved in OSC performance without any deterioration in NOx removal performance even though one half of the noble metal was directly supported on the core-shell support of the present invention and the other half of the noble metal was supported on the other material. [Industrial applicability]

[0149] As described above, according to the present invention, it is possible to provide a core-shell support exhibiting both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity, a process for producing the core-shell support, a catalyst for exhaust gas purification using the core-shell support, a process for producing the catalyst, and a process for exhaust gas purification using the catalyst for exhaust gas purification.The core-shell support of the present invention and the exhaust gas purification catalyst using the core-shell support of the present invention offer both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity as described above, thus enabling both sufficiently good oxygen storage / release capacity (OSC) and sufficiently good NOx removal activity to be exhibited. For example, by bringing an exhaust gas from an internal combustion engine into contact with such an exhaust gas purification catalyst of the present invention, the exhaust gas purification catalyst of the present invention can exhibit both sufficiently high oxygen storage / release capacity (OSC) and sufficiently high NOx removal activity, and can sufficiently remove harmful gases such as NOx contained in the exhaust gas.

[0150] Accordingly, the core-shell support, the method for producing the core-shell support, the catalyst for exhaust gas purification using the core-shell support, the method for producing the catalyst, and the method for exhaust gas purification using the catalyst for exhaust gas purification of the present invention can be suitably used as a core-shell support for removing harmful components such as harmful gases (hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx)) contained in the exhaust gas emitted from, for example, an internal combustion engine in an automobile or the like, as a method for producing the core-shell support, as a catalyst for exhaust gas purification using the core-shell support, as a method for producing the catalyst, as an exhaust gas purification method using the catalyst for exhaust gas purification, and the like.

Claims

[1] Core-shell support, comprising: a core comprising at least one oxygen storage / release material selected from alumina-doped ceria-zirconia-based solid solutions; and a shell comprising a rare earth zirconium oxide-based composite oxide represented by a composition formula: (R 1-x Ce x )2Zr2O 7+x , where R represents a rare earth element which is at least one element selected from the group consisting of La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y, and x represents a number from 0.0 to 0.8, and with which an outer side of the core is coated, wherein the rare earth zirconium oxide-based composite oxide contains crystal particles having a pyrochlore structure, and the composite oxide based on rare earth zirconium oxide has an average crystal diameter of 3 to 9 nm, wherein an amount of the rare earth zirconium oxide-based composite oxide forming the shell is 4 to 24 parts by mass based on 100 parts by mass of the at least one oxygen storage / release material forming the core. [2] The core-shell carrier according to claim 1, wherein x in the composition formula is a number from 0.5 to 0.

7. [3] The core-shell support according to claim 1 or 2, wherein Re in the composition formula is at least one element selected from the group consisting of La, Nd, Pr and Y. [4] Catalyst for exhaust gas purification, comprising: the core-shell carrier according to one of claims 1 to 3; and a precious metal supported on the core-shell carrier. [5] The exhaust gas purification catalyst according to claim 4, wherein the noble metal is Rh. [6] Catalyst for exhaust gas purification, comprising: a substrate; and a catalyst layer arranged on the substrate, wherein the catalyst layer comprises the core-shell support according to any one of claims 1 to 3, aluminum oxide and a noble metal. [7] Catalyst for exhaust gas purification according to claim 6, wherein the catalyst layer comprising the core-shell support, the alumina and the noble metal is a rhodium-containing catalyst layer containing Rh as the noble metal, and a palladium-containing catalyst layer containing an alumina-doped solid solution based on ceria-zirconia, alumina and Pd is arranged between the substrate and the rhodium-containing catalyst layer. [8] A method for producing the core-shell carrier according to any one of claims 1 to 3, comprising: a solution preparation step of preparing a solution containing a rare earth element salt and a zirconium salt; a first coating step of bringing the prepared solution into contact with a powder of at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina to obtain a core-shell powder supporting the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth-zirconia-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding; and a second coating step to bring the prepared solution into contact with the obtained core-shell powder to obtain the core-shell powder which additionally supports the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth zirconium oxide-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding, wherein the core-shell support is obtained by performing the second coating step until an amount of the rare earth zirconium oxide-based composite oxide constituting the shell after calcination into the oxide reaches 4 to 24 parts by mass based on 100 parts by mass of the oxygen storage / release material constituting the core. [9] A method for producing the exhaust gas purification catalyst according to claim 4 or 5, comprising: a solution preparation step of preparing a solution containing a rare earth element salt and a zirconium salt; a first coating step of bringing the prepared solution into contact with a powder of at least one oxygen storage / release material selected from ceria-zirconia-based solid solutions doped with alumina to obtain a core-shell powder supporting the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth-zirconia-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding; and a second coating step to bring the prepared solution into contact with the obtained core-shell powder to obtain the core-shell powder which additionally supports the prepared solution in an amount which, after calcination into an oxide, results in 1 to 8 parts by mass of the rare earth zirconium oxide-based composite oxide forming part of the shell, based on 100 parts by mass of the oxygen storage / release material forming the core, followed by calcination at a temperature in a range of 600 to 1100 °C and then grinding, wherein the core-shell support is obtained by performing the second coating step until an amount of the shell-forming rare earth zirconium oxide-based composite oxide after calcination into the oxide reaches 4 to 24 parts by mass based on 100 parts by mass of the core-forming oxygen storage / release material, and then the catalyst for exhaust gas purification is obtained by bringing a precious metal salt solution into contact with the core-shell carrier. [10] A method for purifying exhaust gases, comprising: Purifying an exhaust gas emitted from an internal combustion engine by bringing the exhaust gas into contact with the exhaust gas purifying catalyst according to any one of claims 4 to 7.

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