JP2018038999A - Exhaust gas purification catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for purifying exhaust gas using an OCS material having both an oxygen storage capacity and an oxygen absorption / release rate while having sufficient heat resistance. The present invention is a catalyst for purifying exhaust gas having a base material and a catalyst coat layer formed on the base material, and a ceria-zirconia-based composite oxide having a pyrochlore structure is applied to the base material capacity. It is contained in the catalyst coat layer in an amount of 5 to 100 g / L, the secondary particle size (D50) of the ceria-zirconia-based composite oxide is 3 to 7 μm, and the ceria-zirconia-based composite oxide contains placeodim. May be related to the catalyst for purifying exhaust gas. [Selection diagram] Fig. 1

Description

  The present invention relates to an exhaust gas purification catalyst.

  Exhaust gas discharged from internal combustion engines such as automobiles contains harmful gases such as carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons (HC). For the exhaust gas purifying catalyst (so-called three-way catalyst) for decomposing such harmful gases, a ceria-zirconia-based composite oxide or the like is used as a co-catalyst having an oxygen storage capacity (OSC: Oxygen Storage Capacity). Oxygen storage materials (OSC materials) such as ceria-zirconia-based composite oxides control the air-fuel ratio (A / F) in a micro space by absorbing and releasing oxygen and reducing the purification rate due to exhaust gas composition fluctuations. It has a suppressing effect.

  Conventionally, an OSC material used for an exhaust gas purification catalyst has a sufficient oxygen storage capacity and heat resistance for maintaining the ability to absorb and release oxygen over a long period of time, and even after being exposed to a high temperature for a long period of time. It has been required to exhibit a sufficiently excellent oxygen storage capacity. In response to this requirement, Patent Document 1 proposes a ceria-zirconia composite oxide having a pyrochlore structure in which the primary particle diameter of ceria-zirconia composite oxide, the content ratio of cerium and zirconium, and the like are specified. Specifically, the primary particles in the ceria-zirconia composite oxide having a particle size of 1.5 to 4.5 μm are 50% or more on the basis of the number of particles with respect to the total primary particles of the composite oxide. -The content ratio of cerium and zirconium in the zirconia-based composite oxide is in the range of 43:57 to 55:45 in terms of molar ratio ([cerium]: [zirconium]), and in the atmosphere at a temperature condition of 1100 ° C. 2θ = 14.5 ° diffraction line and 2θ = 29 ° diffraction line obtained from an X-ray diffraction pattern using CuKα obtained by X-ray diffraction measurement after heating for 5 hours. The intensity ratio {I (14/29) value} and the intensity ratio {I (28/29) value} of 2θ = 28.5 ° diffraction line and 2θ = 29 ° diffraction line are as follows: 14/29) value c ≧ 0.015 and I (28/29) value ≦ 0.08 are described. Ceria-zirconia composite oxides are described. In the ceria-zirconia composite oxide described in Patent Document 1, the primary particle diameter is specified, but the secondary particle diameter is not specifically described.

  Patent Document 2 includes a crystal particle having a pyrochlore structure of a ceria-zirconia composite oxide, and a crystal having a fluorite structure of a ceria-zirconia composite oxide existing on the particle surface. -A crystal having a fluorite structure of a zirconia-based composite oxide is integrated with crystal grains having a pyrochlore structure of the ceria-zirconia-based composite oxide and containing more zirconia than ceria. A composite oxide material is described, and it is described that a ceria-zirconia composite oxide having a pyrochlore structure with an average secondary particle diameter of 11 μm was prepared.

  Recently, with the physique reduction of the catalyst, the OSC material used for the exhaust gas purification catalyst not only has sufficient heat resistance and oxygen storage capacity, but also has a sufficiently high oxygen absorption / release rate to exhibit faster behavior. It is demanded.

  However, in the conventional ceria-zirconia-based composite oxide, if the crystal structure is a fluorite structure, the oxygen storage / release rate is large, but the oxygen storage capacity is small, and if the crystal structure is a pyrochlore structure, Although the oxygen storage capacity is large, the oxygen storage / release rate is small, and it has been difficult to achieve both the oxygen storage capacity and the oxygen storage / release rate.

JP-A-2015-34113 JP 2014-114196 A

  As described above, in the conventional exhaust gas purification catalyst, in the ceria-zirconia-based composite oxide used as the OSC material, when the crystal structure is a fluorite structure, the oxygen storage / release rate is high, but the oxygen storage capacity is small. In addition, when the crystal structure is a pyrochlore structure, although the oxygen storage capacity is large, the oxygen storage / release rate is low, so it is difficult to achieve both the oxygen storage capacity and the oxygen storage / release rate while having sufficient heat resistance. Met. Therefore, an object of the present invention is to provide an exhaust gas purifying catalyst using an OCS material having both sufficient heat resistance and having both an oxygen storage capacity and an oxygen absorption / release rate.

  As a result of various studies on means for solving the above problems, the present inventors have determined that the secondary particle diameter (D50) of the ceria-zirconia-based composite oxide having a pyrochlore structure is within a specific range. The present inventors have found that an oxide can have both an oxygen storage capacity and an oxygen absorption / release rate while having sufficient heat resistance, and completed the present invention.

That is, the gist of the present invention is as follows.
(1) An exhaust gas purifying catalyst having a base material and a catalyst coat layer formed on the base material, the ceria-zirconia-based composite oxide having a pyrochlore structure in an amount of 5 to 100 g / In the catalyst coat layer in an amount of L, the secondary particle diameter (D50) of the ceria-zirconia composite oxide is 3 to 7 μm, and the ceria-zirconia composite oxide may contain praseodymium. Exhaust gas purification catalyst.
(2) The exhaust gas purification catalyst includes a start-up catalyst (S / C) and an underfloor catalyst (UF / C) installed behind the S / C with respect to the flow direction of the exhaust gas. The exhaust gas-purifying catalyst according to (1), which is S / C or UF / C of the system.
(3) The exhaust gas-purifying catalyst is S / C, the S / C has at least two catalyst coat layers, and the ceria-zirconia composite oxide is 5 to 50 g / The exhaust gas-purifying catalyst according to (2), which is contained in the uppermost layer of the catalyst coat layer in an amount of L.
(4) The exhaust gas-purifying catalyst is S / C, the S / C has at least two catalyst coat layers, and the ceria-zirconia composite oxide is added in an amount of 5 to 30 g / The exhaust gas-purifying catalyst according to (2), which is contained in at least one layer other than the uppermost layer of the catalyst coat layer in an amount of L.
(5) The exhaust gas-purifying catalyst is UF / C, the UF / C has at least two catalyst coat layers, and the ceria-zirconia composite oxide is added in an amount of 5 to 20 g / The exhaust gas-purifying catalyst according to (2), which is contained in the uppermost layer of the catalyst coat layer in an amount of L.

  According to the present invention, it is possible to provide an exhaust gas purifying catalyst using an OSC material having both sufficient heat resistance and having both an oxygen storage capacity and an oxygen absorption / release rate.

FIG. 1 shows an initial oxygen absorption / release amount (OSC) (bar graph) of the ceria-zirconia composite oxides of Example 1-2 and Comparative Example 1-5, and an exhaust gas purifying catalyst using these composite oxides. Shows the maximum oxygen storage amount (Cmax) (line graph). FIG. 2 shows the relationship between the oxygen storage / release amount (OSC) in the initial stage (0 to 13 seconds) and the maximum oxygen storage amount (Cmax). FIG. 3 shows the maximum oxygen storage amount (Cmax) of S / C in Examples 4 and 7 and Comparative Example 6-10. FIG. 4 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper layer coating and the maximum oxygen storage amount (Cmax). FIG. 5 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper coat and T50-NOx. FIG. 6 shows the relationship between the addition amount of the OSC material (ceria-zirconia composite oxide of Example 2) in the lower layer coat and the NOx emission amount at the time of A / F switching. FIG. 7 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the lower layer coat and the steady NOx purification rate. FIG. 8 shows the steady HC purification rate of UF / C of Examples 13 and 17 and Comparative Examples 16-18. FIG. 9 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper layer coating and the steady HC purification rate. FIG. 10 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper layer coat and T50-NOx.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

The exhaust gas-purifying catalyst of the present invention includes a base material, and a ceria-zirconia-based composite oxide (Ce ₂ Zr ₂ O ₇ : hereinafter referred to as a pyrochlore-type ceria-zirconia-based composite oxide) formed on the base material and having a pyrochlore structure. Or a catalyst coating layer containing a predetermined amount of pyrochlore CZ).

  In the ceria-zirconia composite oxide, “having a pyrochlore structure” means that a crystalline phase (pyrochlore phase) having a pyrochlore-type ordered arrangement structure of cerium ions and zirconium ions is formed. A part of the cerium ion and the zirconium ion may be substituted with an additional element such as praseodymium. The arrangement structure of the pyrochlore phase can be specified by having peaks at positions where the 2θ angles of the X-ray diffraction pattern using CuKα are 14.5 °, 28 °, 37 °, 44.5 °, and 51 °, respectively. it can. Here, the “peak” means that the height from the baseline to the peak top is 30 cps or more. Further, when obtaining the diffraction line intensity, the calculation is performed by subtracting the average diffraction line intensity of 2θ = 10 to 12 ° as the background value from the value of each diffraction line intensity.

  In the ceria-zirconia-based composite oxide having a pyrochlore structure, the content ratio of the crystal phase regularly arranged in the pyrochlore type with respect to the total crystal phase determined by the peak intensity ratio of the X-ray diffraction pattern is 50% or more, particularly 80% or more. It is preferable. Methods for preparing ceria-zirconia composite oxides having a pyrochlore structure are known to those skilled in the art.

The pyrochlore phase (Ce ₂ Zr ₂ O ₇ ) of the ceria-zirconia composite oxide has an oxygen defect site, and when an oxygen atom enters the site, the pyrochlore phase changes to a κ phase (Ce ₂ Zr ₂ O ₈ ). To do. On the other hand, the κ phase can change into a pyrochlore phase by releasing oxygen atoms. The oxygen storage capacity of the ceria-zirconia composite oxide is due to the absorption and release of oxygen by mutually changing the phase between the pyrochlore phase and the κ phase.

Here, it is known that the κ phase of the ceria-zirconia-based composite oxide changes into a crystalline phase having a fluorite structure (CeZrO ₄ : fluorite-type phase) by rearrangement. During lean, the pyrochlore CZ is likely to undergo a phase change to the fluorite type phase via the κ phase.

In the X-ray diffraction (XRD) measurement using CuKα of the crystal phase of the ceria-zirconia composite oxide, the diffraction line of 2θ = 14.5 ° is a diffraction line belonging to the (111) plane of the regular phase (κ phase) The diffraction line at 2θ = 29 ° is a combination of the diffraction line belonging to the (222) plane of the regular phase and the diffraction line belonging to the (111) plane of the ceria-zirconia solid solution having no pyrochlore phase. Therefore, the I (14/29) value, which is the intensity ratio between the two diffraction lines, can be used as an index indicating the abundance of the ordered phase. In the present invention, the XRD measurement is usually performed after the ceria-zirconia composite oxide to be measured is heated in the atmosphere at 1100 ° C. for 5 hours (high temperature durability test). In the present invention, in the ceria-zirconia composite oxide, 2θ = 14.5 ° determined from an X-ray diffraction pattern using CuKα obtained by X-ray diffraction measurement after heating at 1100 ° C. for 5 hours in the air. The intensity ratio I (14/29) value between the diffraction line and the diffraction line of 2θ = 29 ° is preferably 0.017 or more from the viewpoint of maintaining a good ordered phase and oxygen storage capacity after the durability test. . Based on the κ-phase PDF card (PDF2: 01-070-4048) and the pyrochlore phase PDF card (PDF2: 01-075-2694), the complete κ-phase I (14/29) value is 0.04. The I (14/29) value of the complete pyrochlore phase can be calculated as 0.05. Further, in the XRD measurement using CuKα of the crystal phase of the ceria-zirconia composite oxide, the diffraction line of 2θ = 28.5 ° is a diffraction line belonging to the (111) plane of CeO ₂ alone, 2θ = The I (28/29) value, which is the intensity ratio between the diffraction line of 28.5 ° and the diffraction line of 2θ = 29 °, can be used as an index indicating the degree of phase separation of CeO ₂ from the composite oxide. . In the present invention, in the ceria-zirconia-based composite oxide, 2θ = 28.5 ° obtained from an X-ray diffraction pattern using CuKα obtained by X-ray diffraction measurement after heating at 1100 ° C. in the air for 5 hours. The intensity ratio I (28/29) value between the diffraction line and the diffraction line of 2θ = 29 ° is preferably 0.05 or less from the viewpoint of suppression of ceria phase separation and oxygen storage capacity after the durability test. .

  The ceria-zirconia composite oxide having a pyrochlore structure has a secondary particle diameter (D50) of 3 to 7 μm, preferably 3 to 6 μm, more preferably 3 to 5 μm. When the Pyrochlore CZ has a secondary particle size (D50) in this range, it has sufficient heat resistance and a high oxygen storage capacity compared to those having a secondary particle size (D50) not in this range. The oxygen absorption / release rate can be significantly improved while maintaining. In the ceria-zirconia-based composite oxide having a fluorite structure, there is no such relationship between the secondary particle diameter and the oxygen absorption / release rate. Therefore, the secondary particle diameter (D50) is specified in the pyrochlore CZ. It is an unexpected effect specific to pyrochlore CZ that the oxygen absorption / release rate is significantly improved by setting the range. In Pyrochlore CZ, the influence of secondary particle size is very large due to the fast oxygen internal diffusion characteristic of pyrochlore structure. On the other hand, the heat resistance, which is in a trade-off relationship, is the oxygen absorption / release rate with respect to the secondary particle size. Shows different sensitivities and sufficiently high heat resistance is maintained. As a result, in the pyrochlore CZ, the secondary particle diameter (D50) is set within a specific range, so that high oxygen storage is achieved while having high heat resistance. It is presumed that the oxygen absorption / release rate could be significantly improved while maintaining the capacity. Therefore, in the present invention, when the pyrochlore CZ has a secondary particle diameter (D50) of 3 to 7 μm, it is possible to achieve both an oxygen storage capacity and an oxygen absorption / release rate while having sufficient heat resistance. The release rate can be significantly improved.

  In the present invention, “secondary particles” are aggregates of primary particles, and “primary particles” generally refer to the smallest particles that constitute a powder. The primary particles can be determined by observing with an electron microscope such as a scanning electron microscope (SEM). In the present invention, the primary particle size of the pyrochlore CZ is usually smaller than the secondary particle size, and the primary particle size (D50) is preferably 1.5 to 6.0 μm, more preferably 1.70. ˜5.0 μm. Here, the primary particle diameter (D50) means an average primary particle diameter when the number distribution is measured. On the other hand, in the present invention, the secondary particle diameter (D50) means that the secondary particle diameter is a 50% cumulative particle diameter (also referred to as median diameter or D50). The secondary particle size (D50) is, for example, a volume particle size distribution obtained by measuring by a laser diffraction scattering method, and a volume particle size of 50% in a cumulative volume distribution curve with the total volume being 100% (that is, Volume-based cumulative 50% diameter).

  Pyrochlore CZ having a secondary particle size (D50) in a specific range is obtained, for example, by mixing raw materials to obtain a precipitate, drying and firing the obtained precipitate, pulverizing to obtain a powder, and obtaining the obtained powder. It is obtained by pressure molding, reducing treatment, and pulverizing to a predetermined secondary particle size (D50). The molded body can be pulverized by, for example, a ball mill, a vibration mill, a stream mill, a pin mill, or the like.

  In pyrochlore CZ, the molar ratio (Zr / Ce) of zirconium (Zr) to cerium (Ce) is 1.13 <Zr / Ce <1.30.

Pyrochlore CZ may contain praseodymium (Pr), and preferably contains praseodymium in addition to cerium and zirconium. Praseodymium has a negative ΔG (Gibbs free energy) represented by the formula: Pr ₆ O ₁₁ → 3Pr ₂ O ₃ + O ₂ , so ΔG is positive. Formula: 2CeO ₂ → Ce ₂ O _This is considered to facilitate the reduction reaction of CeO ₂ represented by ₃ + 0.5O ₂ . When the pyrochlore CZ contains praseodymium, the pyrochlore CZ preferably contains 0.5-5 mol% praseodymium relative to the total amount of total cations, and the molar ratio of Zr to (Ce + Pr) is preferably 1.13 <Zr / (Ce + Pr) <1.30.

  The pyrochlore CZ may contain an element other than praseodymium (Pr) as an additional element other than cerium (Ce) and zirconium (Zr). The additional element other than praseodymium is not particularly limited, and examples thereof include rare earth elements other than cerium and praseodymium and alkaline earth metals. Examples of rare earth elements other than cerium and praseodymium include scandium (Sc), yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), Ytterbium (Yb), lutetium (Lu), and the like. Among them, La, Nd, Y, and the like tend to increase the interaction with the noble metal when the noble metal is supported, and the affinity tends to increase. Sc is preferred. Examples of alkaline earth metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Among these, when a noble metal is supported, From the viewpoint that the interaction tends to be strong and the affinity tends to increase, Mg, Ca, and Ba are preferable. The content of the additional element is usually 5 mol% or less based on the total amount of all the cations of pyrochlore CZ.

The specific surface area of the pyrochlore CZ is preferably 5 m ² / g or less from the viewpoint of good interaction with a noble metal, oxygen storage capacity and heat resistance. The specific surface area can be calculated as a BET specific surface area from the adsorption isotherm using the BET isotherm adsorption equation.

  The tap density of the pyrochlore CZ is preferably 1.5 g / cc to 2.5 g / cc.

As the catalyst metal used in the catalyst coat layer, any catalyst metal exhibiting catalytic activity for CO and HC oxidation and / or NOx reduction can be used, and examples thereof include platinum group noble metals. Examples of the platinum group noble metal include ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt), and it is particularly preferable to use Rh, Pt and Pd. . The supported amount may be the same as that of the conventional exhaust gas purification catalyst, but is preferably 0.01 to 5% by weight with respect to the exhaust gas purification catalyst. In the catalyst coat layer, the pyrochlore CZ may be used as a carrier for supporting the catalyst metal. The catalyst coat layer may contain a carrier material other than the pyrochlore CZ as a carrier. As a support material other than pyrochlore CZ, any metal oxide generally used as a catalyst support, for example, alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), Titania (TiO ₂ ), lantana (La ₂ O ₃ ), or a combination thereof can be used. As the loading method, general loading methods such as an impregnation loading method, an adsorption loading method, and a water absorption loading method can be used.

  The exhaust gas purifying catalyst has a pyrochlore CZ content in the catalyst coating layer in an amount of 5 to 100 g / L with respect to the base material capacity, from the viewpoint of improving the oxygen absorption / release rate improvement effect obtained with respect to the amount used and the exhaust gas purifying ability. Included.

  The exhaust gas-purifying catalyst has at least one catalyst coat layer, but preferably has two catalyst coat layers, an upper layer and a lower layer. In a preferred embodiment, the exhaust gas-purifying catalyst has a base material, a lower catalyst coat layer formed on the base material, and an upper catalyst coat layer formed on the lower catalyst coat layer and containing pyrochlore CZ. .

In an embodiment in which the exhaust gas purifying catalyst has two catalyst coat layers, the lower catalyst coat layer is preferably composed of palladium (Pd) as a catalyst metal, alumina (Al ₂ O ₃ ) as a carrier, alumina, and the like. (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), and a combination with a lantana (La ₂ O ₃ ) composite oxide, and the upper catalyst coat layer contains rhodium (Rh) as the catalyst metal. As a support, for example, a composite oxide of pyrochlore CZ, alumina (Al ₂ O ₃ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ) and lantana (La ₂ O ₃ ) Including combinations. In this case, the catalyst metal is preferably supported on a composite oxide of alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), and lantana (La ₂ O ₃ ).

The base material used for the exhaust gas purifying catalyst is not particularly limited, and a honeycomb-shaped material having a number of commonly used cells can be used. As the material, cordierite (2MgO · 2Al ₂ Examples thereof include ceramic materials having heat resistance such as O ₃ · 5SiO ₂ ), alumina, zirconia, and silicon carbide, and metal materials made of metal foil such as stainless steel. The coating of the catalyst coating layer on the substrate is performed by a known method, for example, by pouring a slurry prepared by suspending each material in distilled water and a binder and pouring the unnecessary portion with a blower. Can do.

  The exhaust gas purifying catalyst of the present invention can be used in an exhaust gas purifying catalyst system including two or more catalysts. Preferably, the exhaust gas purifying catalyst of the present invention includes a start-up catalyst (also referred to as S / C, a start-up converter, etc.) attached immediately below the internal combustion engine, and the S / C with respect to the flow direction of the exhaust gas. It is used for an exhaust gas purification catalyst system including two catalysts, an underfloor catalyst (also referred to as UF / C, underfloor converter, underfloor catalyst, etc.) installed at the rear. That is, the exhaust gas purifying catalyst of the present invention can be used as S / C and / or UF / C of an exhaust gas purifying catalyst system including S / C and UF / C.

Startup catalyst (S / C)
When the exhaust gas purifying catalyst of the present invention is used as S / C, the S / C preferably has at least two catalyst coat layers (that is, a multilayer catalyst coat), and the catalyst coat layer has at least one layer. Includes pyrochlore CZ. The S / C preferably has two catalyst coat layers, an upper layer and a lower layer. As the catalyst metal used for the S / C catalyst coat layer, the above-mentioned catalysts for the exhaust gas purification catalyst are preferable, and the uppermost layer of the S / C catalyst coat layer contains Rh and Pd as catalyst metals, and other than the uppermost layer. More preferably, at least one layer contains Pd as the catalytic metal.

S / C containing pyrochlore CZ in the uppermost layer of the multilayer catalyst coat
In one embodiment, the S / C includes pyrochlore CZ in the uppermost layer of the catalyst coat layer, and in a preferred embodiment, the S / C includes pyrochlore CZ in the upper layer of the upper and lower catalyst coat layers. In this case, the catalyst coat layer other than the uppermost layer of S / C may or may not contain pyrochlore CZ. In this embodiment, the S / C contains pyrochlore CZ in the uppermost layer that is easily in contact with the exhaust gas, so that the OSC can be quickly developed against fine atmospheric fluctuations of the exhaust gas, and the catalyst can be stoichiometric for a long time. Can do. Further, since the pyrochlore CZ exhibits a sufficient OSC ability with a small amount, the catalyst can be reduced in size without increasing the pressure loss of the catalyst.

  In this embodiment, the S / C preferably contains 5 to 50 g / L of pyrochlore CZ in the uppermost layer of the catalyst coating layer with respect to the base material capacity. When S / C contains 5 g / L or more of pyrochlore CZ in the uppermost layer of the catalyst coating layer with respect to the base material capacity, it has sufficient OSC ability and high NOx purification ability (catalytic activity), and 50 g / L When included below, it has high OSC ability and sufficient NOx purification ability.

  The S / C of this embodiment is, for example, an internal combustion engine that controls A / F in the vicinity of stoichiometry, and is preferably used under conditions of 400 ° C. or higher.

  In a preferred embodiment, the S / C has at least two catalyst coat layers, the uppermost layer of the catalyst coat layer being a catalyst metal that is Rh and Pd, and 5 to 50 g / L with respect to the substrate capacity. The pyrochlore CZ and other support materials are included, and at least one layer other than the uppermost layer includes a catalyst metal that is Pd and a support material other than the pyrochlore CZ.

  In a more preferred embodiment, the S / C has two catalyst coat layers, an upper layer and a lower layer, and the upper layer of the catalyst coat layer has a catalyst metal of Rh and Pd and 5 to 50 g based on the substrate capacity. / L pyrochlore CZ and other support materials, and the lower layer of the catalyst coat layer contains a catalyst metal that is Pd and a support material other than pyrochlore CZ.

S / C containing pyrochlore CZ in a layer other than the top layer of the multilayer catalyst coat
In another embodiment, the S / C includes pyrochlore CZ in at least one layer other than the uppermost layer of the catalyst coat layer, and in a preferred embodiment, pyrochlore CZ is included in the lower layer of the upper and lower catalyst coat layers. . In this case, the uppermost layer of S / C may or may not contain pyrochlore CZ. In this embodiment, the S / C includes pyrochlore CZ in a layer other than the uppermost layer, so that both high NOx purification ability during steady operation and high NOx purification ability during A / F switching can be achieved. The material has high NOx purification ability at low temperatures where it was difficult to obtain an effect, and this embodiment is useful for reducing NOx emissions during mode running.

  In this embodiment, S / C preferably contains 5 to 30 g / L of pyrochlore CZ relative to the base material capacity in at least one layer other than the uppermost layer of the catalyst coat layer. When S / C contains 5-30 g / L of pyrochlore CZ with respect to the substrate capacity in at least one layer other than the uppermost layer of the catalyst coating layer, it has a high NOx purification capacity at the time of steady operation and high at the time of A / F switching Both NOx purification capabilities can be achieved.

  The S / C of this embodiment is, for example, an internal combustion engine that controls A / F in the vicinity of stoichiometry, and is preferably used under conditions of 400 ° C. or higher.

  In a preferred embodiment, the S / C has at least two catalyst coat layers, and the uppermost layer of the catalyst coat layer includes a catalyst metal that is Rh and Pd and a support material other than pyrochlore CZ, and is not the uppermost layer. At least one layer of Pd includes a catalytic metal that is Pd, 5 to 30 g / L of the pyrochlore CZ with respect to the substrate capacity, and a support material other than the pyrochlore CZ.

  In a more preferred embodiment, the S / C has two catalyst coat layers, an upper layer and a lower layer, and the upper layer of the catalyst coat layer includes a catalyst metal that is Rh and Pd and a support material other than pyrochlore CZ. The lower layer of the catalyst coat layer includes a catalyst metal that is Pd, 5 to 30 g / L of pyrochlore CZ with respect to the substrate capacity, and a support material other than pyrochlore CZ.

Underfloor catalyst (UF / C)
UF / C is provided downstream of S / C. Since the exhaust gas after the reaction at S / C flows into UF / C, UF / C purifies exhaust gas (especially HC) that cannot be purified by S / C in an atmosphere with a small amount of oxygen in the exhaust gas. .

  When the exhaust gas purifying catalyst of the present invention is used as UF / C, UF / C has at least two catalyst coat layers, and preferably contains pyrochlore CZ as the uppermost layer of the catalyst coat layer. The catalyst coat layer other than the uppermost layer of UF / C may or may not contain pyrochlore CZ. The UF / C preferably has two catalyst coat layers, an upper layer and a lower layer, and includes pyrochlore CZ in the upper layer. In this embodiment, UF / C includes pyrochlore CZ in the uppermost layer that is easily in contact with exhaust gas, so that the HC purification capability during steady operation is enhanced. Furthermore, since the pyrochlore CZ exhibits a sufficient amount of HC purification ability with a small amount, the catalyst can be reduced in size without increasing the pressure loss of the catalyst. As the catalyst metal used for the catalyst coat layer of UF / C, those described above for the exhaust gas purification catalyst are preferable, and the uppermost layer of the catalyst coat layer of UF / C contains Rh as the catalyst metal, and is at least one other than the uppermost layer. More preferably, the layer contains Pd as the catalytic metal.

  UF / C preferably contains pyrochlore CZ in the uppermost layer of the catalyst coating layer in an amount of 5 to 20 g / L based on the substrate capacity. When UF / C contains 5-20 g / L of pyrochlore CZ in the uppermost layer of the catalyst coating layer with respect to the base material capacity, both high HC purification ability and high NOx purification ability during steady operation can be achieved.

  The UF / C of this embodiment is, for example, an internal combustion engine that controls A / F in the vicinity of the stoichiometry, and is preferably used under conditions of 350 ° C. or higher.

  In a preferred embodiment, the UF / C has at least two catalyst coat layers, the top layer of the catalyst coat layer being a catalyst metal that is Rh and a pyrochlore CZ of 5-20 g / L relative to the substrate capacity. And at least one layer other than the uppermost layer includes a catalyst metal that is Pd and a support material other than pyrochlore CZ.

  In a more preferred embodiment, the UF / C has two catalyst coat layers, an upper layer and a lower layer, and the upper layer of the catalyst coat layer is 5 to 20 g / L based on the catalyst metal being Rh and the substrate capacity. Pyrochlore CZ and other support materials, and the lower layer of the catalyst coat layer contains a catalyst metal that is Pd and a support material other than Pyrochlore CZ.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.

<Preparation of ceria-zirconia composite oxide>
(1) Synthesis of praseodymium-added pyrochlore-type ceria-zirconia composite oxide (Pr-added pyrochlore CZ) 129.7 g of cerium nitrate hexahydrate, 99.1 g of zirconium oxynitrate dihydrate, praseodymium nitrate hexahydrate 5 0.4 g and 36.8 g of 18% hydrogen peroxide water were dissolved in 500 cc of ion-exchanged water, and a hydroxide precipitate was obtained by reverse coprecipitation using 340 g of 25% aqueous ammonia. The precipitate is separated with a filter paper, the obtained precipitate is dried at 150 ° C. for 7 hours in a drying furnace to remove moisture, calcined at 500 ° C. for 4 hours in an electric furnace, pulverized, and ceria-zirconia-praseodymia A composite oxide was obtained.

Next, the obtained powder was molded by applying a pressure of 2000 kgf / cm ² using a pressure molding machine (Wet-CIP) to obtain a molded body of ceria-zirconia-praseodymia composite oxide.

  Next, the obtained molded body was reduced in a graphite crucible containing activated carbon in an Ar atmosphere at 1700 ° C. for 5 hours to obtain praseodymium-added pyrochlore-type ceria-zirconia-based composite oxide (Pr-added pyrochlore CZ). Prepared. The obtained Pr-added pyrochlore CZ was then fired in an electric furnace at 500 ° C. for 5 hours.

(2) Synthesis of praseodymium-doped fluorite-type ceria-zirconia composite oxide (Pr-doped fluorite CZ) 129.7 g of cerium nitrate hexahydrate, 99.1 g of zirconium oxynitrate dihydrate, praseodymium nitrate hexahydrate 5.4 g of the product and 36.8 g of 18% hydrogen peroxide water were dissolved in 500 cc of ion-exchanged water, and a hydroxide precipitate was obtained by reverse coprecipitation using 340 g of 25% ammonia water. The precipitate is separated with a filter paper, the obtained precipitate is dried at 150 ° C. for 7 hours in a drying furnace to remove moisture, and calcined at 900 ° C. for 5 hours in an electric furnace, and is added with praseodymium-added fluorite-type ceria-zirconia. A composite oxide (Pr-added fluorite CZ) was obtained.

Example 1
Using a vibration mill, 200 g / batch of Pr-added pyrochlore CZ was pulverized by setting the pulverization conditions so that the secondary particle diameter (D50) was 3 μm, and the secondary particle diameter (D50) was 3.3 μm. A Pr-added pyrochlore CZ of Example 1 was prepared.

Example 2
Using a stream mill, 200 g / batch of Pr-added pyrochlore CZ was pulverized by setting the pulverization conditions so that the secondary particle size (D50) was 5 μm, and the secondary particle size (D50) was 4.9 μm. The Pr-added pyrochlore CZ of Example 2 was prepared.

Comparative Example 1
Using a vibration mill, 200 g / batch of Pr-added pyrochlore CZ was pulverized by setting the pulverization conditions so that the secondary particle diameter (D50) was 1 μm, and the secondary particle diameter (D50) was 0.5 μm. A Pr-added pyrochlore CZ of Comparative Example 1 was prepared.

Comparative Example 2
Using a stream mill, 200 g / batch of Pr-added pyrochlore CZ was pulverized by setting the pulverization conditions so that the secondary particle size (D50) was 11 μm, and the secondary particle size (D50) was 11.2 μm. The Pr-added pyrochlore CZ of Comparative Example 2 was prepared.

Comparative Example 3
Using a vibration mill, 200 g / batch of Pr-added fluorite CZ was pulverized by setting the pulverization conditions so that the secondary particle diameter (D50) was 1 μm, and the secondary particle diameter (D50) was 1. A Pr-added fluorite CZ of Comparative Example 3 having a thickness of 0 μm was prepared.

Comparative Example 4
Using a stream mill, 200 g / batch of Pr-added fluorite CZ was pulverized by setting the pulverization conditions so that the secondary particle size (D50) was 5 μm, and the secondary particle size (D50) was 5. A Pr-added fluorite CZ of Comparative Example 4 having a size of 1 μm was prepared.

Comparative Example 5
Using a stream mill, 200 g / batch of Pr-added fluorite CZ was pulverized by setting the pulverization conditions so that the secondary particle size (D50) was 8 μm, and the secondary particle size (D50) was 10. A Pr-added fluorite CZ of Comparative Example 5 having a thickness of 9 μm was prepared.

<Evaluation of Ceria-Zirconia Composite Oxide>
<X-ray diffraction (XRD) measurement>
The ceria-zirconia composite oxide obtained in Example 1-2 and Comparative Example 1-5 was heat-treated in the atmosphere at 1100 ° C. for 5 hours (high temperature endurance test). The crystal phase was measured by X-ray diffraction method. An X-ray diffraction pattern was measured using TTR-III (manufactured by Rigaku Corporation) as an X-ray diffractometer, and I (14/29) value and I (28/29) value were obtained. Table 1 shows the results obtained for the ceria-zirconia composite oxides of Example 1-2 and Comparative Example 1-2.

  From Table 1, in the ceria-zirconia-based composite oxides of Example 1-2 and Comparative Example 1-2, since the I (14/29) value is almost equivalent, the secondary particle diameter of pyrochlore CZ (D50) Has a small effect on heat resistance, and the ceria-zirconia composite oxide of Example 1-2 has sufficient heat resistance.

<Oxygen absorption and release measurement test: OSC evaluation>
The oxygen absorption / release amount (OSC) of the ceria-zirconia composite oxide obtained in Example 1-2 and Comparative Example 1-5 was measured as follows.

The endurance test was heat-treated at 1050 ° C. for 5 hours, and the gas composition during the endurance test was alternately switched between 8% −CO + 10% −H ₂ O⇔20% −O ₂ + 10% −H ₂ O every 15 minutes. It was.

Furthermore, the weight ratio of the ceria-zirconia composite oxide of Example 1-2 and Comparative Example 1-5 after the durability test and Pd / Al ₂ O ₃ powder supporting Pd (0.25 wt%) was 1: 1. The powder obtained was physically mixed by using a pressure molding machine (Wet-CIP apparatus) and molded under a pressure of 1000 kgf / cm ² , and pulverized and sieved to produce 1 mm square pellets.

The test was carried out using 3.0 g of pellets placed in a fixed bed flow apparatus and using an evaluation gas with a total flow rate of 15 L. From the initial (0 to 13 seconds) CO ₂ generation amount during the flow of 2% -CO (N ₂ balance) after treatment with 1% -O ₂ (N ₂ balance), the reaction formula of CO + 1 / 2O ₂ → CO ₂ Based on this, the amount of O ₂ released from the ceria-zirconia composite oxide was calculated, and the oxygen absorption / release rate was evaluated by obtaining the initial oxygen absorption / release amount (OSC). Release of oxygen from cerium is expressed by a reaction formula of 2CeO ₂ → Ce ₂ O ₃ +1/2 O ₂ .

  The results are shown in FIG. FIG. 1 shows an initial oxygen absorption / release amount (OSC) (bar graph) of the ceria-zirconia composite oxides of Example 1-2 and Comparative Example 1-5, and an exhaust gas purifying catalyst using these composite oxides. Shows the maximum oxygen storage amount (Cmax) (line graph). From FIG. 1 (bar graph), in the ceria-zirconia composite oxide (Comparative Examples 3 to 5) having a fluorite structure, the initial oxygen storage / release amount (OSC) does not increase even when the secondary particle diameter is controlled. In contrast, in the ceria-zirconia composite oxides (Examples 1 and 2 and Comparative Examples 1 and 2) having a pyrochlore structure, the range of the secondary particle diameter (D50) is a specific range. Thus, it was shown that the initial oxygen absorption / release amount (OSC) was significantly increased, and the oxygen absorption / release rate was significantly improved.

<Engine bench evaluation>
Exhaust gas purification catalysts were prepared and evaluated using the ceria-zirconia composite oxides of Example 1-2 and Comparative Example 1-5.

(1) Catalyst preparation The following materials were used as catalyst materials:
Ceria-zirconia composite oxide of Example 1-2 and Comparative Example 1-5 Al ₂ O ₃ : La ₂ O ₃ (1 wt%) composite Al ₂ O ₃
ACZL: Composite oxide of Al ₂ O ₃ (30 wt%), CeO ₂ (20 wt%), ZrO ₂ (45 wt%) and La ₂ O ₃ (5 wt%) Rh: Noble metal content 2.75 wt % Rhodium nitrate (Rh) aqueous solution (Cataler Co., Ltd.)
Pd: An aqueous palladium nitrate (Pd) solution having a noble metal content of 8.8% by weight (manufactured by Cataler)
Honeycomb substrate: 875 cc (600H / 3-9R-08) cordierite honeycomb substrate (manufactured by Denso Corporation).

The catalyst was prepared as follows:
(A) Lower layer: Pd (0.69) / ACZL (45) + Al ₂ O ₃ (40) (numbers in parentheses indicate coat amount (g / L) relative to substrate capacity)
Pd / ACZL in which Pd is supported on ACZL is prepared by an impregnation method using ACZL and palladium nitrate, suspended in distilled water, and Al ₂ O ₃ and Al ₂ O ₃ binders are added. A slurry was prepared. The prepared slurry was poured onto the substrate, and unnecessary portions were blown off with a blower to coat the substrate wall surface. The coating contained Pd 0.69 g / L, Al ₂ O ₃ 40 g / L, and ACZL 45 g / L with respect to the substrate capacity. After coating, the coating was dried for 2 hours with a drier maintained at 120 ° C., and then baked for 2 hours in an electric furnace at 500 ° C. to prepare a lower layer coat.

(B) Upper layer: Rh (0.10) / ACZL (110) + Al ₂ O ₃ (28) + Ceria-zirconia composite oxide (20) of Example 1-2 and Comparative Example 1-5
Using ACZL and rhodium nitrate, Rh / ACZL in which Rh is supported by ACZL is prepared by an impregnation method, suspended in distilled water, and the Al ₂ O ₃ and Al ₂ O ₃ binders are stirred. Finally, each ceria-zirconia composite oxide of Example 1-2 and Comparative Example 1-5 was added to prepare corresponding slurries. Each obtained slurry was poured into the substrate coated with (a) above, and unnecessary portions were blown off with a blower to coat the lower layer coat on the substrate wall surface. For coating, Rh is 0.10 g / L, Al ₂ O ₃ is 28 g / L, ACZL is 110 g / L, and each ceria-zirconia of Example 1-2 and Comparative Example 1-5 with respect to the substrate capacity 20 g / L of the system complex oxide was included. After coating, after drying for 2 hours with a drier maintained at 120 ° C., the mixture was fired for 2 hours in an electric furnace at 500 ° C., and each ceria-zirconia composite oxide of Example 1-2 and Comparative Example 1-5 was obtained. The corresponding catalysts of Example 1-2 and Comparative Example 1-5 used were obtained.

(2) Durability test Using a 1UR-FE engine (manufactured by Toyota Motor Corporation), a deterioration acceleration test was conducted for 25 hours at a catalyst bed temperature of 1000 ° C. The exhaust gas composition adjusted the throttle opening and engine load, and promoted deterioration by repeating rich to stoichiometric to lean at a constant cycle.

(3) OSC test The catalyst after the endurance test of (2) above is mounted on a 2AZ-FE engine (manufactured by Toyota Motor Corporation), the incoming gas temperature is set to 600 ° C, and the A / F of the incoming gas atmosphere is adjusted. 14.1 and 15.1 are feedback-controlled with the target to periodically amplify, and from the difference between the stoichiometric point and the A / F sensor output, the excess / deficiency of oxygen is expressed by the formula: OSC (g) = 0.23 × ΔA / The maximum oxygen storage amount (Cmax) was calculated by F × injected fuel amount. Here, there is a correlation between the initial (0-13 seconds) oxygen storage / release amount (OSC) and the maximum oxygen storage amount (Cmax) of the catalyst, and the initial (0-13 seconds) oxygen storage / release. It is known that the maximum oxygen storage amount (Cmax) increases when the amount (OSC) is large (see FIG. 2). Therefore, the oxygen storage / release rate can be evaluated by obtaining the maximum oxygen storage amount (Cmax) of the catalyst. The results are shown in FIG. FIG. 1 shows an initial oxygen absorption / release amount (OSC) (bar graph) of the ceria-zirconia composite oxides of Example 1-2 and Comparative Example 1-5, and an exhaust gas purifying catalyst using these composite oxides. Shows the maximum oxygen storage amount (Cmax) (line graph).

  From FIG. 1, in the engine bench evaluation of the catalyst using the ceria-zirconia composite oxide of Example 1-2 and Comparative Examples 1, 2, and 4, the ceria of Example 1-2 and Comparative Example 1-5 The same result as that of the zirconia composite oxide was confirmed. Specifically, from FIG. 1 (line graph), in the present invention, by setting the secondary particle diameter (D50) of the ceria-zirconia composite oxide having a pyrochlore structure to a specific range (3 to 7 μm), The maximum oxygen storage capacity (Cmax) is significantly increased with respect to pyrochlore CZ and ceria-zirconia composite oxide having a fluorite structure whose secondary particle size is not in this range, and thus the oxygen storage / release rate is significantly improved. Was shown. In Pyrochlore CZ, the influence of secondary particle size is very large due to the fast oxygen internal diffusion characteristic of pyrochlore structure. On the other hand, the heat resistance, which is in a trade-off relationship, is the oxygen absorption / release rate with respect to the secondary particle size. Shows different sensitivities and sufficiently high heat resistance is maintained. As a result, in the pyrochlore CZ, the secondary particle diameter (D50) is set within a specific range, so that high oxygen storage is achieved while having high heat resistance. It is presumed that the oxygen absorption / release rate could be significantly improved while maintaining the capacity.

  In the ceria-zirconia-based composite oxide having a pyrochlore structure, the secondary particle diameter (D50) is 3 to 7 μm, so that both oxygen storage capacity and oxygen absorption / release rate can be achieved while having sufficient heat resistance. The exhaust gas purifying catalyst using such ceria-zirconia composite oxide also has such an effect.

<Startup catalyst (S / C)>
The following materials were used as catalyst materials:
Al ₂ O ₃ : La ₂ O ₃ (4% by weight) composite Al ₂ O ₃ (manufactured by Sasol)
ACZ-1: of Al ₂ O ₃ (30 wt%), CeO ₂ (27 wt%), ZrO ₂ (35 wt%), La ₂ O ₃ (4 wt%) and Y ₂ O ₃ (4 wt%) Complex oxide (manufactured by Solvay)
_{ACZ-2: Al 2 O 3} (30 wt%), _CeO 2 (20 wt%), _ZrO 2 (44 _{wt%), Nd 2 O 3 (} 2 _{wt%), La 2 O 3 (} 2 wt%) and Composite oxide of Y ₂ O ₃ (2% by weight) (Daiichi Rare Element Chemical Industries, Ltd.)
OSC material:
-Ceria-zirconia composite oxide of Example 2 and Comparative Example 1-2 (Pr-added pyrochlore CZ)
・ ACZ-2
CZ: Composite oxide of CeO ₂ (30 wt%), ZrO ₂ (60 wt%), La ₂ O ₃ (5 wt%) and Y ₂ O ₃ (5 wt%) (manufactured by Solvay)
Fluorite-type CZ: Pr-added fluorite CZ having a secondary particle diameter (D50) of 6.1 μm prepared in the same manner as in Comparative Example 4
Honeycomb substrate: cordierite honeycomb substrate of 875 cc (600 cells hexagonal wall thickness 2 mil)

  In order to evaluate the performance of S / C in which the ceria-zirconia composite oxide of the present invention was added to the uppermost layer as an OSC material, the S / C of Example 3-7 and Comparative Example 6-11 was changed as follows. Prepared.

Comparative Example 6
(A) Preparation of lower layer coat Using ACZ-1 and palladium nitrate, Pd / ACZ-1 in which Pd is supported on ACZ-1 is prepared by an impregnation method, and a predetermined amount of Pd / ACZ-1, Al ₂ is prepared. Slurry 1 was prepared by adding and suspending O ₃ , barium sulfate and an Al ₂ O ₃ binder in distilled water while stirring. The prepared slurry 1 was poured into a substrate, and unnecessary portions were blown off with a blower to coat the substrate wall surface. The coating contained Pd 0.38 g / L, Al ₂ O ₃ 40 g / L, ACZ-1 45 g / L, and barium sulfate 5 g / L with respect to the substrate capacity. After coating, the coating was dried for 2 hours with a drier maintained at 120 ° C., and then baked for 2 hours in an electric furnace at 500 ° C. to prepare a lower layer coat.

(B) Preparation of upper layer coat Using ACZ-2 and rhodium nitrate, Rh / ACZ-2 in which Rh is supported on ACZ-2 is prepared by an impregnation method, and a predetermined amount of palladium nitrate, Rh / ACZ-2 is prepared. Then, Al ₂ O ₃ and Al ₂ O ₃ binder were added to distilled water with stirring and suspended to prepare slurry 2. The obtained slurry 2 was poured into the substrate coated with (a) above, and unnecessary portions were blown off with a blower to coat the lower layer coat on the substrate wall surface. The coating contained Rh 0.3 g / L, Pd 0.2 g / L, ACZ-2 72 g / L, and Al ₂ O ₃ 63 g / L with respect to the substrate capacity. After coating, it was dried for 2 hours with a drier maintained at 120 ° C. and then baked for 2 hours in an electric furnace at 500 ° C. to obtain S / C in which the upper layer coat was formed on the lower layer coat.

Example 3-6
In Examples 3, 4, 5 and 6, the slurry 2 for forming the upper layer coat was obtained by adding the ceria-zirconia-based composite oxide (Pr-added pyrochlore CZ) of Example 2 as the OSC material to the substrate capacity. Each S / C was obtained in the same manner as in Comparative Example 6 except that the coating amounts were 16 g / L, 24 g / L, 48 g / L and 55 g / L, respectively.

Example 7
Comparative Example 6 except that the ceria-zirconia composite oxide of Example 2 was added as an OSC material to the slurry 1 for forming the lower layer coat so as to have a coating amount of 24 g / L based on the substrate capacity. Similarly, S / C was obtained.

Comparative Example 7
To the slurry 2 for forming the upper layer coat, the ceria-zirconia composite oxide (Pr-added pyrochlore CZ) of Comparative Example 2 was added as an OSC material so as to have a coat amount of 24 g / L based on the substrate capacity. Except for the above, S / C was obtained in the same manner as in Comparative Example 6.

Comparative Example 8
To the slurry 2 for forming the upper layer coat, the ceria-zirconia composite oxide (Pr-added pyrochlore CZ) of Comparative Example 1 was added as an OSC material so as to have a coat amount of 24 g / L with respect to the substrate capacity. Except for the above, S / C was obtained in the same manner as in Comparative Example 6.

Comparative Example 9
An S / C was obtained in the same manner as in Comparative Example 6 except that CZ was added as an OSC material to the slurry 2 for forming the upper layer coat so as to have a coat amount of 25 g / L with respect to the substrate capacity.

Comparative Example 10
An S / C was obtained in the same manner as in Comparative Example 6 except that ACZ-2 as an OSC material was added to the slurry 2 for forming the upper layer coat so as to have a coating amount of 24 g / L with respect to the base material capacity. It was.

Comparative Example 11
S / C was obtained in the same manner as in Comparative Example 6 except that fluorite-type CZ was added as an OSC material to slurry 2 for forming the upper layer so as to have a coating amount of 24 g / L with respect to the substrate capacity. It was.

Table 2 shows the addition position and addition amount (coating amount) of the OSC material and the characteristics of the OSC material for the S / C of Example 3-7 and Comparative Example 6-11.

  Durability tests were performed on the S / Cs of Example 3-7 and Comparative Example 6-11, and performance evaluation was performed.

<Durability test>
Each S / C of Example 3-7 and Comparative Example 6-11 was mounted on the exhaust system of a V-type 8-cylinder engine, and the exhaust gas in each of stoichiometric and lean atmospheres for a certain period of time at a catalyst bed temperature of 950 ° C. for 50 hours. An endurance test was conducted by repeatedly flowing (a 3: 1 ratio).

<Performance evaluation>
Each S / C after the durability test was mounted on an L4 engine, and the following performance was evaluated.
OSC:
Each S / C after the endurance test is mounted on an L4 engine, the incoming gas temperature is set to 500 ° C., and the air-fuel ratio (A / F) is feedback controlled to target 14.4 and 15.1, thereby purifying the exhaust gas. The maximum oxygen storage amount (Cmax) was determined in the same manner as the OSC test of the catalyst for use, and this was evaluated as OSC.
T50-NOx:
When exhaust gas of A / F = 14.4 is supplied to each S / C after the durability test and the temperature is raised to 500 ° C. under high Ga conditions (Ga = 35 g / s), the NOx purification rate is 50%. Was measured (T50-NOx), and the catalytic activity was evaluated.

  The results are shown in FIGS. FIG. 3 shows the maximum oxygen storage amount (Cmax) of S / C in Examples 4 and 7 and Comparative Example 6-10. FIG. 4 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper layer coating and the maximum oxygen storage amount (Cmax). FIG. 5 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper coat and T50-NOx.

  From FIG. 3, it was shown that S / C using the ceria-zirconia composite oxide of the present invention significantly increased OSC compared to those using other OSC materials (Example 4 and comparison). Example 7-10). Since the ceria-zirconia composite oxide of the present invention has a high OSC ability, it is suggested that the catalyst can be reduced in size without increasing the pressure loss. Further, it is shown that the OSC ability of S / C is higher when the ceria-zirconia-based composite oxide of the present invention is included in the uppermost layer of the catalyst coat layer that is easily contacted with exhaust gas than when it is included in the lower layer. (Examples 4 and 7).

  Further, from FIG. 4, the OSC ability of S / C increases according to the amount of the ceria-zirconia-based composite oxide of the present invention in the upper layer coat, but on the other hand, from FIG. Decreases as the amount of the ceria-zirconia composite oxide of the present invention in the upper layer coat increases. 4 and 5, the S / C containing the ceria-zirconia composite oxide of the present invention in the uppermost layer of the catalyst coating layer is such that the addition amount can achieve both good OSC ability and NOx purification ability. A range of 5 to 50 g / L is preferred.

  Next, in order to evaluate the performance of S / C in which the ceria-zirconia composite oxide of the present invention was added as an OSC material to a layer other than the uppermost layer, the S / C of Example 8-12 and Comparative Example 12-15 was used. Was prepared as follows.

Example 8-11
In Examples 8, 9, 10 and 11, the slurry 1 for forming the lower layer coat was prepared by adding the ceria-zirconia composite oxide (Pr-added pyrochlore CZ) of Example 2 to 6 g / Each S / C was obtained in the same manner as in Comparative Example 6 except that the coating amounts were L, 12 g / L, 24 g / L, and 35 g / L.

Example 12
Example 12 was prepared in the same manner as Example 3.

Comparative Example 12
Comparative Example 12 was prepared in the same manner as Comparative Example 6.

Comparative Examples 13 and 14
In Comparative Examples 13 and 14, the slurry 1 for forming the lower layer coat, the ceria-zirconia-based composite oxide (Pr-added pyrochlore CZ) of Comparative Example 2 with respect to the substrate capacity, 9 g / L and 20 g / L, respectively. Each S / C was obtained in the same manner as in Comparative Example 6 except that it was added so as to have an L coating amount.

Comparative Example 15
S / C was obtained in the same manner as in Comparative Example 6 except that fluorite type CZ was added to slurry 1 for forming the lower layer coat so as to have a coating amount of 6 g / L with respect to the substrate capacity.

Table 3 shows the addition position and addition amount (coating amount) of the OSC material, and the characteristics of the OSC material for the S / C of Examples 8-12 and Comparative Examples 12-15.

  Durability tests were conducted on the S / Cs of Example 8-12 and Comparative Example 12-15, and performance evaluation was performed.

<Durability test>
Each S / C of Example 8-12 and Comparative Example 12-15 was mounted on the exhaust system of a V-type 8-cylinder engine, and the exhaust gas in each of stoichiometric and lean atmospheres was supplied for a certain period of time at a catalyst bed temperature of 950 ° C. for 50 hours. An endurance test was conducted by repeatedly flowing (a 3: 1 ratio).

<Performance evaluation>
Each S / C after the durability test was mounted on an L4 engine, and the following performance was evaluated.
Steady NOx purification rate: The NOx purification rate during steady operation at A / F = 14.1 and 500 ° C. was calculated.
NOx purification ability at the time of A / F switching: The amount of NOx discharged when feedback control was performed with A / F set to 14.1 and 15.1 was measured. The inlet gas temperature was set to 500 ° C.

  The results are shown in Table 3, FIG. 6 and FIG. FIG. 6 shows the relationship between the addition amount of the OSC material (ceria-zirconia composite oxide of Example 2) in the lower layer coat and the NOx emission amount at the time of A / F switching. FIG. 7 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the lower layer coat and the steady NOx purification rate.

  From Table 3 and FIG. 6, S / C using the ceria-zirconia-based composite oxide of the present invention significantly reduces NOx emissions during A / F switching compared to other OSC materials. It was shown that. In addition, regarding the steady NOx purification ability and the NOx purification ability at the time of A / F switching, when the ceria-zirconia composite oxide of the present invention is included in the lower layer coat, these performances are superior to those in the case where the upper layer coat is included, and mode running Has been shown to be advantageous in reducing NOx emissions at the time. Moreover, from Table 3, FIG.6, and FIG.7, when the addition amount to the lower layer coat | court of the ceria-zirconia type complex oxide of this invention is 5-30 g / L, low NOx discharge | emission amount at the time of A / F switching, It was shown that high steady NOx purification ability can be achieved.

<Under floor catalyst (UF / C)>
The following materials were used as catalyst materials:
Al ₂ O ₃ : La ₂ O ₃ (4% by weight) composite Al ₂ O ₃ (manufactured by Sasol)
_{ACZ-2: Al 2 O 3} (30 wt%), _CeO 2 (20 wt%), _ZrO 2 (44 _{wt%), Nd 2 O 3 (} 2 _{wt%), La 2 O 3 (} 2 wt%) and Composite oxide of Y ₂ O ₃ (2% by weight) (Daiichi Rare Element Chemical Industries, Ltd.)
AZ: of Al ₂ O ₃ (30 wt%), ZrO ₂ (60 wt%), Nd ₂ O ₃ (2 wt%), La ₂ O ₃ (4 wt%) and Y ₂ O ₃ (4 wt%) Composite oxide (Daiichi Rare Element Chemical Industries, Ltd.)
OSC material:
-Ceria-zirconia composite oxide of Example 2 (Pr-added pyrochlore CZ)
・ ACZ-2
Fluorite-type ZC: CeO ₂ (21 wt%), ZrO ₂ (72 wt%), Nd ₂ O ₃ (5.3 wt%) and La ₂ O ₃ (1.7 wt%) fluorite-type ZC Composite oxide (Daiichi Rare Element Chemical Industries, Ltd.)
Honeycomb substrate: cordierite honeycomb substrate of 875 cc (400 cell square wall thickness 4 mil)

  UF / C was prepared as follows.

Comparative Example 16
(A) Preparation of lower layer coat Using ACZ-2 and palladium nitrate, Pd / ACZ-2 in which Pd is supported on ACZ-2 is prepared by an impregnation method, and a predetermined amount of Pd / ACZ-2, Al ₂ is prepared. A slurry 1 was prepared by adding and suspending O ₃ and an Al ₂ O ₃ binder in distilled water while stirring. The prepared slurry 1 was poured into a substrate, and unnecessary portions were blown off with a blower to coat the substrate wall surface. The coating contained Pd 0.53 g / L, Al ₂ O ₃ 40 g / L, and ACZ-2 93 g / L with respect to the substrate capacity. After coating, the coating was dried for 2 hours with a drier maintained at 120 ° C., and then baked for 2 hours in an electric furnace at 500 ° C. to prepare a lower layer coat.

(B) Preparation of upper layer coat Rh / AZ in which Rh is supported on AZ is prepared by an impregnation method using AZ and rhodium nitrate, and a predetermined amount of Rh / AZ, Al ₂ O ₃ and Al ₂ O ₃ system The binder was added to distilled water with stirring and suspended to prepare slurry 2. The obtained slurry 2 was poured into the substrate coated with (a) above, and unnecessary portions were blown off with a blower to coat the lower layer coat on the substrate wall surface. The coating contained Rh 0.4 g / L, Al ₂ O ₃ 35 g / L, and AZ 33 g / L with respect to the substrate capacity. After coating, it was dried for 2 hours with a drier maintained at 120 ° C. and then baked for 2 hours in an electric furnace at 500 ° C. to obtain UF / C in which the upper layer coat was formed on the lower layer coat.

Examples 13-16
In Examples 13, 14, 15, and 16, the ceria-zirconia-based composite oxide (Pr-added pyrochlore CZ) of Example 2 was added to the slurry 2 for forming the upper layer coat, respectively, at 11 g / L with respect to the substrate capacity. Each UF / C was obtained in the same manner as Comparative Example 16 except that the coating amounts were 20 g / L, 31 g / L, and 40 g / L.

Example 17
The same procedure as in Comparative Example 16, except that the ceria-zirconia composite oxide of Example 2 was added to the slurry 1 for forming the lower layer coat so that the coating amount was 11 g / L with respect to the substrate capacity. UF / C was obtained.

Comparative Example 17
UF / C was obtained in the same manner as in Comparative Example 16 except that ACZ-2 was added to the slurry 2 for forming the upper layer coat so as to have a coating amount of 11 g / L with respect to the substrate capacity.

Comparative Example 18
UF / C was obtained in the same manner as in Comparative Example 16 except that fluorite-type ZC was added to slurry 2 for forming the upper layer coat so as to have a coating amount of 11 g / L with respect to the substrate capacity.

Table 4 shows the addition position and addition amount (coat amount) of the OSC material and the characteristics of the OSC material for UF / C of Examples 13-17 and Comparative Examples 16-18.

  Durability tests were performed on UF / C of Examples 13-17 and Comparative Examples 16-18, and performance evaluation was performed.

<Durability test>
The UF / Cs of Examples 13-17 and Comparative Examples 16-18 were mounted on the exhaust system of a V-type 8-cylinder engine, and the exhaust gas in each of the stoichiometric and lean atmospheres was supplied for a certain period of time at a catalyst bed temperature of 950 ° C. for 50 hours. An endurance test was conducted by repeatedly flowing (a 3: 1 ratio).

<Performance evaluation>
Each UF / C after the durability test was mounted on an L4 engine, and the following performance was evaluated.
Steady HC purification rate:
The HC purification rate during steady operation at A / F = 14.4 and 550 ° C. was calculated.
T50-NOx:
When exhaust gas of A / F = 14.4 is supplied to each UF / C after the durability test and the temperature is lowered to 250 ° C. under high Ga conditions (Ga = 35 g / s), the NOx purification rate is 50%. Was measured (T50-NOx), and the catalytic activity was evaluated.

  The results are shown in FIGS. FIG. 8 shows the steady HC purification rate of UF / C of Examples 13 and 17 and Comparative Examples 16-18. FIG. 9 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper layer coating and the steady HC purification rate. FIG. 10 shows the relationship between the amount of OSC material (ceria-zirconia composite oxide of Example 2) in the upper layer coat and T50-NOx.

  FIG. 8 shows that the UF / C using the ceria-zirconia composite oxide of the present invention has a significantly higher steady HC purification rate than those using other OSC materials (Examples). 13, 17 and Comparative Examples 17-18). Since the ceria-zirconia-based composite oxide of the present invention has a high steady HC purification ability, it is suggested that the catalyst can be reduced in size without increasing the pressure loss. In addition, in UF / C, when the ceria-zirconia-based composite oxide of the present invention is included in the uppermost layer of the catalyst coat layer that easily comes into contact with exhaust gas, it is shown that the steady HC purification rate is higher than when it is included in the lower layer. (Examples 13 and 17).

  Further, from FIG. 9, the steady HC purification rate becomes higher according to the addition amount of the ceria-zirconia composite oxide of the present invention in the upper layer coat. On the other hand, from FIG. The addition amount decreases between 20 g / L and 30 g / L. Therefore, in the UF / C containing the ceria-zirconia composite oxide of the present invention in the uppermost layer of the catalyst coating layer, the addition amount is 5 to 20 g in that both good steady HC purification ability and NOx purification ability can be achieved. A range of / L is preferred.

Claims (5)

An exhaust gas purifying catalyst having a base material and a catalyst coat layer formed on the base material,
A ceria-zirconia-based composite oxide having a pyrochlore structure is included in the catalyst coat layer in an amount of 5 to 100 g / L based on the substrate capacity;
The secondary particle diameter (D50) of the ceria-zirconia composite oxide is 3 to 7 μm,
The ceria-zirconia composite oxide may contain praseodymium,
The exhaust gas purifying catalyst.   S of the exhaust gas purification catalyst system, wherein the exhaust gas purification catalyst includes a startup catalyst (S / C) and an underfloor catalyst (UF / C) installed behind the S / C with respect to the flow direction of the exhaust gas. The exhaust gas purifying catalyst according to claim 1, which is / C or UF / C.   The exhaust gas-purifying catalyst is S / C, the S / C has at least two catalyst coat layers, and the amount of the ceria-zirconia composite oxide is 5 to 50 g / L with respect to the substrate capacity. The exhaust gas-purifying catalyst according to claim 2, which is contained in the uppermost layer of the catalyst coating layer.   The exhaust gas-purifying catalyst is S / C, the S / C has at least two catalyst coat layers, and the amount of the ceria-zirconia composite oxide is 5 to 30 g / L with respect to the base material capacity. The exhaust gas purifying catalyst according to claim 2, which is contained in at least one layer other than the uppermost layer of the catalyst coating layer.   The exhaust gas-purifying catalyst is UF / C, the UF / C has at least two catalyst coat layers, and the amount of the ceria-zirconia composite oxide is 5 to 20 g / L with respect to the substrate capacity. The exhaust gas-purifying catalyst according to claim 2, which is contained in the uppermost layer of the catalyst coating layer.

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