JP6863799B2 - Exhaust gas purification catalyst - Google Patents

Description

The present invention relates to a catalyst for purifying exhaust gas.

Exhaust gas emitted from an internal combustion engine of an automobile or the like contains harmful gases such as carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons (HC). As an exhaust gas purification catalyst (so-called three-way catalyst) that decomposes such harmful gas, a ceria-zirconia-based composite oxide or the like is used as an auxiliary catalyst having an oxygen storage capacity (OSC: Oxygen Storage Capacity). Oxygen storage materials (OSC materials) such as ceria-zirconia composite oxides control the air-fuel ratio (A / F) in a micro space by absorbing and releasing oxygen, and reduce the purification rate due to fluctuations in exhaust gas composition. Has a suppressive effect.

Conventionally, the OSC material used as a catalyst for purifying exhaust gas has sufficient oxygen storage capacity and heat resistance to maintain oxygen absorption / release ability for a long period of time, and further, even after being exposed to a high temperature for a long time. It was required to exhibit sufficiently excellent oxygen storage capacity. In response to this requirement, Patent Document 1 proposes a ceria-zirconia-based composite oxide having a pyrochloro structure, which specifies the primary particle size of the ceria-zirconia-based composite oxide, the content ratio of cerium and zirconium, and the like. Specifically, the primary particles having a particle size of 1.5 to 4.5 μm in the ceria-zirconia-based composite oxide are 50% or more of all the primary particles of the composite oxide on the basis of the number of particles, and ceria. -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 at a temperature condition of 1100 ° C. in the atmosphere. Intensity ratio of 2θ = 14.5 ° diffraction line and 2θ = 29 ° diffraction line determined from the X-ray diffraction pattern using CuKα obtained by X-ray diffraction measurement after heating for 5 hours {I (14/29) ) Value} and the intensity ratio {I (28/29) value} of the 2θ = 28.5 ° diffraction line and the 2θ = 29 ° diffraction line are as follows: I (14/29) value ≧ 0. 015, a ceria-zirconia-based composite oxide characterized by satisfying an I (28/29) value ≤ 0.08 is described. The primary particle size of the ceria-zirconia-based composite oxide described in Patent Document 1 is specified, but the secondary particle size is not specifically described.

Further, Patent Document 2 includes crystal particles having a pyrochloro structure of a ceria-zirconia-based composite oxide and crystals having a fluorite structure of a ceria-zirconia-based composite oxide existing on the surface of the particles, and the ceria A crystal having a fluorite structure of a zirconia-based composite oxide is characterized by containing more zirconia than ceria and being integrated with crystal particles having a pyrochloro structure of the ceria-zirconia-based composite oxide. The composite oxide material is described, and it is described that a ceria-zirconia-based composite oxide having a pyrochlor structure having an average secondary particle diameter of 11 μm was prepared.

Recently, as the catalyst has become smaller, 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 in order to exhibit faster behavior. Is required.

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

Japanese Unexamined Patent Publication No. 2015-34113 Japanese Unexamined Patent Publication No. 2014-114196

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

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

That is, the gist of the present invention is as follows.
(1) A catalyst for purifying exhaust gas having a base material and a catalyst coat layer formed on the base material, and containing 5 to 100 g / g of a ceria-zirconia-based composite oxide having a pyrochloro structure with respect to the base material capacity. The amount of L contained in the catalyst coat layer, the secondary particle size (D50) of the ceria-zirconia-based composite oxide may be 3 to 7 μm, and the ceria-zirconia-based composite oxide may contain placeodim. Catalyst for purifying exhaust gas.
(2) The exhaust gas purification catalyst includes an exhaust gas purification 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 purification catalyst according to (1), which is the S / C or UF / C of the system.
(3) The catalyst for purifying exhaust gas is S / C, and the S / C has at least two catalyst coat layers, and the ceria-zirconia-based composite oxide is 5 to 50 g / g / of the substrate capacity. The exhaust gas purification catalyst according to (2), which is contained in the uppermost layer of the catalyst coat layer in an amount of L.
(4) The catalyst for purifying exhaust gas is S / C, and the S / C has at least two catalyst coat layers, and the ceria-zirconia-based composite oxide is 5 to 30 g / g / of the substrate capacity. The exhaust gas purification 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 catalyst for purifying exhaust gas is UF / C, and the UF / C has at least two catalyst coat layers, and the ceria-zirconia-based composite oxide is 5 to 20 g / g / of the substrate capacity. The exhaust gas purification catalyst according to (2), which is contained in the uppermost layer of the catalyst coat layer in an amount of L.

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

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

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

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

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

In the ceria-zirconia-based composite oxide having a pyrochlore structure, the content ratio of the crystal phases regularly arranged in a pyrochlore type 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. Is preferable. A method for preparing a ceria-zirconia-based composite oxide having a pyrochlore structure is known to those skilled in the art.

The pyrochlore phase (Ce ₂ Zr ₂ O ₇ ) of the ceria-zirconia complex oxide has an oxygen defect site, and when an oxygen atom enters the site, the pyrochlore phase changes to the _{κ phase (Ce 2} Zr ₂ O _8). To do. On the other hand, the κ phase can change to the pyrochlore phase by releasing an oxygen atom. The oxygen storage capacity of the ceria-zirconia complex oxide is due to the mutual phase change between the pyrochlore phase and the κ phase to absorb and release oxygen.

Here, it is known that the κ phase of the ceria-zirconia complex oxide _{undergoes a phase change to a crystal phase having a fluorite structure (CeZrO 4} : fluorite type phase) due to rearrangement, and is particularly hot during leaning. At the time of leaning, the pyrochlor CZ tends to undergo a phase change to a 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 the diffraction line belonging to the (111) plane of the regular phase (κ phase). The diffraction line of 2θ = 29 ° is an overlap 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 pyrochroma phase. Therefore, the I (14/29) value, which is the intensity ratio of the diffraction lines of both, can be used as an index showing the abundance rate of the ordered phase. In the present invention, the XRD measurement is usually performed after heating the ceria-zirconia-based composite oxide to be measured in the air at 1100 ° C. for 5 hours (high temperature durability test). In the present invention, 2θ = 14.5 ° obtained from an X-ray diffraction pattern using CuKα obtained by X-ray diffraction measurement after heating in the air at 1100 ° C. for 5 hours in a ceria-zirconia-based composite oxide. The intensity ratio I (14/29) value between the diffraction line and the diffraction line at 2θ = 29 ° is preferably 0.017 or more from the viewpoint of maintaining a good ordered phase and the oxygen storage capacity after the durability test. .. Based on the κ phase PDF card (PDF 2: 01-070-4048) and the pyrochlore phase PDF card (PDF 2: 01-075-2649), the I (14/29) value of the complete κ phase 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-based composite oxide, the diffraction line of 2θ = 28.5 ° is the diffraction line belonging to the (111) plane of _{CeO 2 alone, so 2θ =} The I (28/29) value, which is the intensity ratio of the 28.5 ° diffraction line and the 2θ = 29 ° diffraction line, can be used as an index indicating the degree of phase separation of _{CeO 2 from the composite oxide.} .. In the present invention, 2θ = 28.5 ° obtained from an X-ray diffraction pattern using CuKα obtained by X-ray diffraction measurement after heating in the air at 1100 ° C. for 5 hours in a ceria-zirconia-based composite oxide. The intensity ratio I (28/29) value between the diffraction line and the diffraction line at 2θ = 29 ° is preferably 0.05 or less from the viewpoint of suppressing the phase separation of ceria and the oxygen storage capacity after the durability test. ..

The ceria-zirconia-based composite oxide having a pyrochlore structure has a secondary particle size (D50) of 3 to 7 μm, preferably 3 to 6 μm, and 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 as compared with those having a secondary particle size (D50) in this range. The oxygen absorption / release rate can be significantly improved while maintaining the oxygen absorption / release rate. In the ceria-zirconia-based composite oxide having a fluorite structure, since there is no such relationship between the secondary particle size and the oxygen absorption / release rate, the secondary particle size (D50) is specified in 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 the secondary particle size is very large due to the characteristic of rapid oxygen internal diffusion peculiar to the pyrochlore structure, while the heat resistance, which is in a trade-off relationship, is the oxygen absorption / release rate with respect to the secondary particle size. Show different sensitivities and maintain sufficiently high heat resistance. As a result, by setting the secondary particle size (D50) in a specific range in pyrochlore CZ, high oxygen storage while having high heat resistance is achieved. It is presumed that the oxygen absorption / release rate could be significantly improved while maintaining the capacity. Therefore, in the present invention, since the pyrochlore CZ has a secondary particle size (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, and in particular, oxygen absorption. The release rate can be significantly improved.

In the present invention, the "secondary particles" are aggregates of primary particles, and the "primary particles" generally refer to the smallest particles constituting the 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. It is ~ 5.0 μm. Here, the primary particle size (D50) means the average primary particle size when the number distribution is measured. On the other hand, in the present invention, the secondary particle size (D50) means that the secondary particle size is a 50% cumulative particle size (also referred to as median size or D50). The secondary particle size (D50) is, for example, a particle size having a volume of 50% in the cumulative volume distribution curve with the total volume as 100% in the volume-based particle size distribution obtained by measuring by the laser diffraction / scattering method (that is,). Volume-based cumulative 50% diameter).

Pyrochlor CZ having a secondary particle size (D50) in a specific range is obtained by, for example, mixing raw materials to obtain a precipitate, drying and calcining the obtained precipitate, and pulverizing to obtain a powder. It is obtained by pressure molding, reduction treatment, and then pulverization 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), preferably praseodymium in addition to cerium and zirconium. Praseodymium has a positive ΔG because the reduction reaction ΔG (Gibbs free energy) represented by the formula: Pr ₆ O ₁₁ → _{3 Pr 2} O 3 + O _{2 is negative, the formula: 2CeO 2} → Ce ₂ O It is considered that the reduction reaction of _{CeO 2} represented by ₃ + 0.5O _{2 is likely to occur.} When the pyrochlore CZ contains praseodymium, the pyrochlore CZ preferably contains 0.5-5 mol% of praseodymium with respect 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.

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 and alkaline earth metals other than cerium and praseodymium. Rare earth elements other than cerium and placeodium include scandium (Sc), yttrium (Y), lantern (La), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), and so on. Examples include yttrium (Yb) and lutetium (Lu). Among them, La, Nd, Y, from the viewpoint that the interaction with the noble metal becomes stronger and the affinity tends to increase when the noble metal is supported. Sc is preferred. Examples of the alkaline earth metal element include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Mg, Ca, and Ba are preferable from the viewpoint that the interaction between the two is strong and the affinity tends to be large. The content of additional elements is typically 5 mol% or less relative to the total total cation content of pyrochlore CZ.

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

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

As the catalyst metal used for the catalyst coat layer, any catalyst metal that exhibits catalytic activity for the oxidation of CO and HC and / or the reduction of NOx 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, pyrochlore CZ may be used as a carrier for supporting the catalyst metal. Further, the catalyst coat layer may contain a carrier material other than pyrochlore CZ as a carrier. As the carrier material other than pyrochloro CZ, any metal oxide generally used as a catalyst carrier, for example, alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), etc. Titania (TiO ₂ ), Lantana (La ₂ O ₃ ), or a combination thereof and the like can be used. As the supporting method, a general supporting method such as an impregnation supporting method, an adsorption supporting method and a water absorption supporting method can be used.

The exhaust gas purification catalyst contains pyrochlore CZ in the catalyst coat layer in an amount of 5 to 100 g / L with respect to the substrate capacity from the viewpoint of the effect of improving the oxygen absorption / release rate obtained with respect to the amount used and the balance of the exhaust gas purification ability. Included in.

The exhaust gas purification 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 purification catalyst has a base material, a lower layer catalyst coat layer formed on the base material, and an upper layer catalyst coat layer formed on the lower layer catalyst coat layer and containing pyrochlore CZ. ..

In the embodiment in which the exhaust gas purification catalyst has two catalyst coat layers, preferably, the lower catalyst coat layer uses palladium (Pd) as a catalyst metal and, for example, alumina (Al ₂ O ₃ ) and alumina as a carrier. It contains a combination of (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ) and lanthana (La ₂ O ₃ ) composite oxides, and the upper catalyst coat layer contains rhodium (Rh) as a catalyst metal. As a carrier, for example, a composite oxide of _{pyrochloro CZ, alumina (Al 2} O ₃ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ) and lanthana (La ₂ O _3). Including combinations with. 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 lanthanum (La ₂ O _3).

The base material used for the exhaust gas purification catalyst is not particularly limited, and a commonly used honeycomb-shaped material having a large number of cells can be used, and the material thereof is cordierite (2MgO ・ 2Al _2). O 3 _· 5SiO _2), alumina, zirconia, and ceramic material having heat resistance such as silicon carbide, metal materials and the like made of metal foil such as stainless steel. The coating of the catalyst coating layer on the base material is carried out by a known method, for example, by pouring a slurry prepared by suspending each material in distilled water and a binder into the base material and blowing off unnecessary parts with a blower. Can be done.

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

Startup catalyst (S / C)
When the exhaust gas purification catalyst of the present invention is used as the S / C, the S / C preferably has at least two catalyst coat layers (that is, a multilayer catalyst coat), and the S / C has the above-mentioned at least one layer of the catalyst coat 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 catalyst coat layer of S / C, the above-mentioned catalyst for purifying exhaust gas is preferable, and the uppermost layer of the catalyst coat layer of S / C contains Rh and Pd as catalyst metals, and other than the uppermost layer. It is more preferable that at least one layer contains Pd as a catalyst metal.

S / C containing pyrochlore CZ in the top layer of the multilayer catalyst coat
In one embodiment, the S / C comprises pyrochlore CZ in the uppermost layer of the catalyst coat layer, and in a preferred embodiment, the pyrochlore CZ is contained in the upper layer of the two catalyst coat layers, the upper layer and the lower layer. 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, which easily comes into contact with the exhaust gas, so that the OSC is quickly expressed in response to the small atmospheric fluctuations of the exhaust gas, and the catalyst is kept stoichiometric for a long time. Can be done. Further, since the pyrochlore CZ exerts a sufficient OSC ability even in a small amount, it is possible to reduce the body size of the catalyst without increasing the pressure loss of the catalyst.

In this embodiment, the S / C preferably contains pyrochlore CZ in the uppermost layer of the catalyst coat layer at 5 to 50 g / L with respect to the substrate volume. When the S / C contains 5 g / L or more of pyrochlore CZ in the uppermost layer of the catalyst coat layer with respect to the substrate capacity, it has sufficient OSC ability and high NOx purification ability (catalytic activity), and also has 50 g / L. Including the following, 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 the A / F in the vicinity of the stoichiometric engine, and is preferably used under the condition of 400 ° C. or higher.

In a preferred embodiment, the S / C has at least two catalyst coated layers, the top layer of which is a catalyst metal which is Rh and Pd, and 5 to 50 g / L relative to the substrate volume. Pyrochloro CZ and other carrier materials are included, and at least one layer other than the uppermost layer contains a catalyst metal which is Pd and a carrier material other than pyrochloro 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 is a catalyst metal which is Rh and Pd, and 5 to 50 g with respect to the substrate capacity. It contains / L pyrochloro CZ and other carrier materials, and the lower layer of the catalyst coat layer contains a catalyst metal which is Pd and a carrier material other than pyrochloro CZ.

S / C containing pyrochlore CZ in layers other than the top layer of the multilayer catalyst coat
In another embodiment, the S / C comprises the pyrochlore CZ in at least one layer other than the uppermost layer of the catalyst coat layer, and in a preferred embodiment, the pyrochlore CZ is contained in the lower layer of the two catalyst coat layers, the upper layer and the lower layer. .. In this case, the uppermost layer of S / C may or may not contain pyrochlore CZ. In this embodiment, since the S / C contains the pyrochlor CZ in a layer other than the uppermost layer, it is possible to achieve both high NOx purification ability during steady operation and high NOx purification ability during A / F switching, and in particular, the conventional OSC. The NOx purification ability is high at a low temperature where it is difficult to obtain an effect with the material, and this embodiment is useful for reducing NOx emissions during mode driving.

In this embodiment, the S / C preferably contains 5 to 30 g / L of pyrochlore CZ in at least one layer other than the uppermost layer of the catalyst coat layer with respect to the substrate volume. When the S / C contains 5 to 30 g / L of pyrochlore CZ in at least one layer other than the uppermost layer of the catalyst coat layer with respect to the substrate capacity, high NOx purification ability during steady operation and high A / F switching are performed. Both NOx purification ability can be achieved.

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

In a preferred embodiment, the S / C has at least two catalyst coat layers, the top layer of the catalyst coat layer containing catalyst metals such as Rh and Pd, and a carrier material other than pyrochloro CZ, other than the top layer. At least one layer of the above contains a catalyst metal which is Pd, a pyrochloro CZ of 5 to 30 g / L with respect to the substrate capacity, and a carrier material other than the pyrochlor 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 contains catalyst metals such as Rh and Pd and a carrier material other than pyrochloro CZ. The lower layer of the catalyst coat layer contains a catalyst metal which is Pd, a pyrochloro CZ of 5 to 30 g / L with respect to the substrate capacity, and a carrier material other than the pyrochlor CZ.

Underfloor catalyst (UF / C)
The UF / C is provided downstream of the S / C. Since the exhaust gas after the reaction in the S / C flows into the UF / C, the UF / C purifies the exhaust gas (particularly HC) that cannot be completely purified by the S / C in an atmosphere where the exhaust gas is low in oxygen. ..

When the exhaust gas purification catalyst of the present invention is used as the UF / C, the UF / C has at least two catalyst coat layers, and preferably contains pyrochlore CZ in the uppermost layer of the catalyst coat layer. The catalyst coat layer other than the top layer of the 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 contains pyrochlore CZ in the upper layer. In this embodiment, the UF / C includes the pyrochlore CZ in the uppermost layer, which is likely to come into contact with the exhaust gas, so that the HC purification ability during steady operation is enhanced. Furthermore, since pyrochlore CZ exhibits sufficient HC purification ability even in a small amount, it is possible to reduce the body size of the catalyst without increasing the pressure loss of the catalyst. As the catalyst metal used for the catalyst coat layer of UF / C, the above-mentioned catalyst for exhaust gas purification is preferable, and the uppermost layer of the catalyst coat layer of UF / C contains Rh as a catalyst metal, and at least one other than the uppermost layer. It is more preferable that the layer contains Pd as a catalyst metal.

The UF / C preferably contains pyrochlore CZ in the uppermost layer of the catalyst coat layer at 5 to 20 g / L with respect to the substrate capacity. When the UF / C contains 5 to 20 g / L of pyrochlore CZ in the uppermost layer of the catalyst coat layer with respect to the substrate capacity, it is possible to achieve both high HC purification ability and high NOx purification ability during steady operation.

The UF / C of this embodiment is, for example, an internal combustion engine that controls the A / F in the vicinity of the stoichiometric engine, 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 of Rh and a pyrochlor CZ of 5 to 20 g / L relative to the substrate volume. And other carrier materials, and at least one layer other than the uppermost layer contains a catalyst metal which is Pd and a carrier material other than pyrochloro 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 a catalyst metal which is Rh and 5 to 20 g / L with respect to the capacity of the base material. Pyrochlor CZ and other carrier materials are included, and the lower layer of the catalyst coat layer contains a catalyst metal which is Pd and a carrier material other than Pyrochrome CZ.

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

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

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

(2) Synthesis of praseodymium-added fluorite-type ceria-zirconia-based composite oxide (Pr-added fluorite CZ) Serium nitrate hexahydrate 129.7 g, zirconium oxynitrate dihydrate 99.1 g, praseodymium nitrate hexahydrate 5.4 g of the product and 36.8 g of 18% hydrogen peroxide solution were dissolved in 500 cc of ion-exchanged water, and 340 g of 25% ammonia water was used to obtain a hydroxide precipitate by the reverse co-precipitation method. The precipitate was separated with a filter paper, and the obtained precipitate was dried in a drying furnace at 150 ° C. for 7 hours to remove water, and then fired in an electric furnace at 900 ° C. for 5 hours to add praseodymium-added fluorite-type ceria-zirconia. A system composite oxide (Pr-added fluorite CZ) was obtained.

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

Example 2
Using a stream mill, 200 g / batch of Pr-added pyrochlore CZ was crushed by setting crushing 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 is pulverized by setting pulverization conditions so that the secondary particle diameter (D50) is 1 μm, and the secondary particle diameter (D50) is 0.5 μm. The 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 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 is pulverized by setting pulverization conditions so that the secondary particle size (D50) is 1 μm, and the secondary particle size (D50) is 1. The Pr-added fluorite CZ of Comparative Example 3 having a size of 0 μm was prepared.

Comparative Example 4
Using a stream mill, 200 g / batch of Pr-added fluorite CZ is pulverized by setting pulverization conditions so that the secondary particle size (D50) is 5 μm, and the secondary particle size (D50) is 5. The 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 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 size of 9 μm was prepared.

<Evaluation of ceria-zirconia composite oxide>
<X-ray diffraction (XRD) measurement>
The ceria-zirconia-based composite oxides obtained in Examples 1-2 and Comparative Examples 1-5 were heat-treated at 1100 ° C. in the air for 5 hours (high temperature durability test), and the treated ceria-zirconia-based composite oxides were subjected to the treatment. The crystal phase was measured by X-ray diffraction. The X-ray diffraction pattern was measured using TTR-III (manufactured by Rigaku Co., Ltd.) as an X-ray diffractometer, and the I (14/29) value and the I (28/29) value were determined. The results obtained for the ceria-zirconia-based composite oxides of Example 1-2 and Comparative Example 1-2 are shown in Table 1.

From Table 1, since the I (14/29) values of the ceria-zirconia-based composite oxides of Example 1-2 and Comparative Example 1-2 were almost the same, the secondary particle size (D50) of pyrochlore CZ was determined. Has a small effect on heat resistance, and the ceria-zirconia-based composite oxide of Example 1-2 has sufficient heat resistance.

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

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

Further ceria Examples 1-2 and Comparative Example 1-5 after the durability test - and zirconia composite oxide, carrying Pd (0.25 wt%) Pd / _Al 2 _{O 3} powder in a weight ratio of 1: 1 ^{The obtained powder was physically mixed in 1 and molded by applying a pressure of 1000 kgf / cm 2} using a pressure molding machine (Wet-CIP device), and pulverized and sieved to prepare 1 mm square pellets.

A 3.0 g pellet was placed in a fixed bed flow device, and a test was carried out using an evaluation gas having a total flow rate of 15 L. From the initial (0 to 13 seconds) CO ₂ generation amount during 1% -O ₂ (N ₂ balance) treatment to 2% -CO (N ₂ balance) distribution, the reaction formula of CO + 1/2 O ₂ → CO _{2 Based on this, the amount of O 2} released from the ceria-zirconia-based composite oxide was calculated, and the initial amount of oxygen absorption / release (OSC) was obtained to evaluate the oxygen absorption / release rate. The release of oxygen from cerium is represented by the reaction formula of _{2 CeO 2} → Ce ₂ O ₃ + 1/2 O 2.

The results are shown in FIG. FIG. 1 shows the initial oxygen absorption / release amount (OSC) (bar graph) of the ceria-zirconia-based composite oxides of Examples 1-2 and Comparative Example 1-5, and the exhaust gas purification catalyst using these composite oxides. The maximum oxygen storage amount (Cmax) (line graph) of is shown. From FIG. 1 (bar graph), in the ceria-zirconia composite oxide having a fluorite structure (Comparative Examples 3 to 5), the initial oxygen absorption / release amount (OSC) did not increase even if the secondary particle size was controlled. However, in the ceria-zirconia-based composite oxide having a pyrochlore structure (Examples 1 and 2 and Comparative Examples 1 and 2), the range of the secondary particle size (D50) is set as a specific range. 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-based composite oxides of Examples 1-2 and Comparative Examples 1-5.

(1) Preparation of catalyst The following materials were used as catalyst materials:
Ceria-zirconia-based composite oxide of Examples 1-2 and Comparative Example 1-5 Al ₂ O ₃ : La ₂ O ₃ (1% by weight) composite Al ₂ O ₃
ACZL: Composite oxide of Al ₂ O ₃ (30% by weight), CeO ₂ (20% by weight), ZrO ₂ (45% by weight) and La ₂ O ₃ (5% by weight) Rh: Precious metal content 2.75% by weight % Rhodium Nitrate (Rh) Aqueous Solution (manufactured by Cataler Co., Ltd.)
Pd: Palladium nitrate (Pd) aqueous solution with a precious metal content of 8.8% by weight (manufactured by Cataler Corporation)
Honeycomb base material: 875 cc (600H / 3-9R-08) cordierite honeycomb base material (manufactured by Denso Corporation).

The catalyst was prepared as follows:
(A) Lower layer: Pd (0.69) / ACZL (45) + Al ₂ O ₃ (40) (The numerical values in parentheses indicate the coating amount (g / L) with respect to the base material capacity).
Using ACZL and palladium nitrate, Pd / ACZL in which Pd was supported on ACZL was prepared by an impregnation method, suspended in distilled water, and Al ₂ O ₃ and Al ₂ O ₃ binders were added. A slurry was prepared. The prepared slurry was poured into a base material, unnecessary parts were blown off with a blower, and the wall surface of the base material was coated. The coating, with respect to the substrate capacity, Pd is 0.69g / L, _Al 2 _{O 3} is to 40g / L, ACZL is contained 45 g / L. After coating, it was dried in a dryer kept at 120 ° C. for 2 hours and then fired in an electric furnace at 500 ° C. for 2 hours to prepare a lower coat.

(B) Upper layer: Rh (0.10) / ACZL (110) + Al ₂ O ₃ (28) + Ceria-zirconia-based composite oxide (20) of Examples 1-2 and Comparative Example 1-5.
Using ACZL and rhodium nitrate, Rh / ACZL in which Rh was carried by ACZL was prepared by an impregnation method, suspended in distilled water, and Al ₂ O ₃ and Al ₂ O ₃ based binders were stirred. Finally, each ceria-zirconia-based composite oxide of Example 1-2 and Comparative Example 1-5 was added to prepare each corresponding slurry. Each of the obtained slurries was poured into the base material coated according to (a) above, unnecessary parts were blown off with a blower, and the undercoat of the base material wall surface was coated. For coating, Rh was 0.10 g / L, Al ₂ O ₃ was 28 g / L, ACZL was 110 g / L, and each ceria-zirconia of Example 1-2 and Comparative Example 1-5 was applied with respect to the substrate volume. 20 g / L of the system composite oxide was contained. After coating, it was dried in a dryer maintained at 120 ° C. for 2 hours, and then calcined in an electric furnace at 500 ° C. for 2 hours to obtain the ceria-zirconia composite oxides of Examples 1-2 and Comparative Example 1-5. 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 floor temperature of 1000 ° C. As for the exhaust gas composition, the throttle opening and the engine load were adjusted, and rich-stoiki-lean was repeated in a fixed cycle to promote deterioration.

(3) OSC test The catalyst after the durability test of (2) above is mounted on a 2AZ-FE engine (manufactured by Toyota Motor Corporation), the entering gas temperature is set to 600 ° C., and the A / F of the entering gas atmosphere is adjusted. Feedback control is performed with 14.1 and 15.1 as targets to periodically oscillate, and the excess or deficiency of oxygen is calculated from the difference between the stoichiometric point and the A / F sensor output. The maximum oxygen storage amount (Cmax) was calculated by calculating from F × the amount of injected fuel. Here, there is a correlation between the initial oxygen uptake and release amount (OSC) of the catalyst and the maximum oxygen uptake (Cmax), and the initial (0 to 13 seconds) oxygen uptake and release. It has been found that when the amount (OSC) is large, the maximum oxygen uptake (Cmax) is large (see FIG. 2). Therefore, the oxygen absorption / release rate can be evaluated by determining the maximum oxygen uptake (Cmax) of the catalyst. The results are shown in FIG. FIG. 1 shows the initial oxygen absorption / release amount (OSC) (bar graph) of the ceria-zirconia-based composite oxides of Examples 1-2 and Comparative Example 1-5, and the exhaust gas purification catalyst using these composite oxides. The maximum oxygen storage amount (Cmax) (line graph) of is shown.

From FIG. 1, also in the engine bench evaluation of the catalyst using the ceria-zirconia-based composite oxide of Examples 1-2 and Comparative Examples 1, 2 and 4, the ceria of Examples 1-2 and Comparative Example 1-5 was also evaluated. Results similar to those of zirconia-based composite oxides were confirmed. Specifically, from FIG. 1 (folded line graph), in the present invention, the secondary particle size (D50) of the ceria-zirconia-based composite oxide having a pyrochlore structure is set to a specific range (3 to 7 μm). The maximum oxygen occlusion (Cmax) is significantly increased for pyrochlore CZ whose secondary particle size is not in this range and the ceria-zirconia-based composite oxide having a fluorite structure, and thus the oxygen absorption / release rate is significantly improved. It was shown that it was done. In pyrochlore CZ, the influence of the secondary particle size is very large due to the characteristic of rapid oxygen internal diffusion peculiar to the pyrochlore structure, while the heat resistance, which is in a trade-off relationship, is the oxygen absorption / release rate with respect to the secondary particle size. Show different sensitivities and maintain sufficiently high heat resistance. As a result, by setting the secondary particle size (D50) in a specific range in pyrochlore CZ, high oxygen storage while having high heat resistance is achieved. It is presumed that the oxygen absorption / release rate could be significantly improved while maintaining the capacity.

In a ceria-zirconia-based composite oxide having a pyrochlore structure, by setting the secondary particle size (D50) to 3 to 7 μm, it is possible to achieve both oxygen storage capacity and oxygen absorption / release rate while having sufficient heat resistance. A catalyst for purifying exhaust gas using such a ceria-zirconia-based 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% by weight), CeO ₂ (27% by weight), ZrO ₂ (35% by weight), La ₂ O ₃ (4% by weight) and Y ₂ O ₃ (4% by weight) Composite oxide (manufactured by Solvay)
ACZ-2: Al ₂ O ₃ (30% by weight), CeO ₂ (20% by weight), ZrO ₂ (44% by weight), Nd ₂ O ₃ (2% by weight), La ₂ O ₃ (2% by weight) and Y ₂ O ₃ (2% by weight) composite oxide (manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.)
OSC material:
-Ceria-zirconia-based composite oxide of Example 2 and Comparative Example 1-2 (Pr-added pyrochlore CZ)
-The ACZ-2
CZ: _{Composite oxide of CeO 2} (30% by weight), ZrO ₂ (60% by weight), La ₂ O ₃ (5% by weight) and Y ₂ O ₃ (5% by weight) (manufactured by Solvay)
-Fluorite type CZ: Pr-added fluorite CZ having a secondary particle size (D50) of 6.1 μm prepared in the same manner as in Comparative Example 4.
Honeycomb base material: 875 cc (600 cell hexagon wall thickness 2 mil) cordierite honeycomb base material

In order to evaluate the performance of the S / C in which the ceria-zirconia-based composite oxide of the present invention is added to the uppermost layer as the OSC material, the S / Cs of Examples 3-7 and Comparative Examples 6-11 are set as follows. Prepared.

Comparative Example 6
(A) Preparation of lower layer coat Pd / ACZ-1 in which Pd is supported on ACZ-1 is prepared by an impregnation method using ACZ-1 and palladium nitrate, and a predetermined amount of Pd / ACZ-1, Al _{2 is prepared.} O ₃ , barium sulfate and Al ₂ O ₃ based binder were added to distilled water with stirring and suspended to prepare slurry 1. The prepared slurry 1 was poured into a base material, unnecessary parts were blown off with a blower, and the wall surface of the base material was coated. The coating, with respect to the substrate capacity, Pd is 0.38g / L, _Al 2 _{O 3} is 40g / L, ACZ-1 was to 45 g / L, barium sulfate contained 5 g / L. After coating, it was dried in a dryer kept at 120 ° C. for 2 hours and then fired in an electric furnace at 500 ° C. for 2 hours to prepare a lower coat.

(B) Preparation of upper layer coat Using ACZ-2 and rhodium nitrate, Rh / ACZ-2 in which Rh was supported on ACZ-2 was prepared by an impregnation method, and a predetermined amount of palladium nitrate and Rh / ACZ-2 were prepared. , Al ₂ O ₃ and Al ₂ O ₃ based binders were added to distilled water with stirring and suspended to prepare slurry 2. The obtained slurry 2 was poured into the base material coated according to (a) above, unnecessary parts were blown off with a blower, and the undercoat of the base material wall surface was coated. The coating contained 0.3 g / L of Rh, 0.2 g / L of Pd, 72 g / L of ACZ-2, and _{63 g / L of Al 2} O _{3 with respect to the substrate volume.} After coating, the mixture was dried in a dryer maintained at 120 ° C. for 2 hours and then fired in an electric furnace at 500 ° C. for 2 hours to obtain an S / C in which the upper coat was formed on the lower coat.

Example 3-6
In Examples 3, 4, 5 and 6, the ceria-zirconia-based composite oxide (Pr-added pyrochlore CZ) of Example 2 was added as an OSC material to the slurry 2 for forming the upper layer coat with respect 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
Compared to Comparative Example 6 except that the ceria-zirconia-based 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 with respect to the substrate capacity. S / C was obtained in the same manner.

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

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

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

Comparative Example 10
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 substrate volume. It was.

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

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

The durability test was carried out on the S / C of Example 3-7 and Comparative Example 6-11, and the performance was evaluated.

<Durability test>
Each S / C of Example 3-7 and Comparative Example 6-11 was attached to the exhaust system of a V8 engine, and the exhaust gas of each atmosphere of stoichiometric and lean was exhausted for a certain period of time at a catalyst floor temperature of 950 ° C. for 50 hours. The durability test was carried out by repeatedly flowing (3: 1 ratio) at a time.

<Performance evaluation>
Each S / C after the durability test was mounted on the L4 engine and the following performance was evaluated.
OSC:
Each S / C after the durability test is mounted on the L4 engine, the entering gas temperature is set to 500 ° C., and the air-fuel ratio (A / F) is feedback-controlled with the target of 14.4 and 15.1 to purify the exhaust gas. The maximum oxygen occlusion (Cmax) was determined in the same manner as in 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%. The temperature (T50-NOx) was measured to evaluate the catalytic activity.

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

From FIG. 3, it was shown that the S / C using the ceria-zirconia-based composite oxide of the present invention had a significantly increased OSC as compared with the one using other OSC materials (Example 4 and comparison). Example 7-10). Since the ceria-zirconia-based 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 was shown that the OSC ability of S / C is higher when the ceria-zirconia-based composite oxide of the present invention is contained in the uppermost layer of the catalyst coat layer which easily comes into contact with exhaust gas than when it is contained 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 added in the upper coat, but on the other hand, from FIG. 5, the NOx purification ability at low temperature is shown. Decreases as the amount of the ceria-zirconia-based composite oxide of the present invention added in the upper coat increases. From FIGS. 4 and 5, in the S / C containing the ceria-zirconia-based composite oxide of the present invention in the uppermost layer of the catalyst coat layer, the addition amount thereof can achieve both good OSC ability and NOx purification ability. The range of 5 to 50 g / L is preferable.

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

Example 8-11
In Examples 8, 9, 10 and 11, 6 g / g of the ceria-zirconia-based composite oxide (Pr-added pyrochlore CZ) of Example 2 was added to the slurry 1 for forming the lower coat with respect to the substrate volume, respectively. 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 in Example 3.

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

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

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

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

Durability tests were carried out on the S / Cs of Examples 8-12 and Comparative Examples 12-15, and the performance was evaluated.

<Durability test>
Each S / C of Example 8-12 and Comparative Example 12-15 was attached to the exhaust system of a V8 engine, and the exhaust gas of each atmosphere of stoichiometric and lean was exhausted for a certain period of time at a catalyst floor temperature of 950 ° C. for 50 hours. The durability test was carried out by repeatedly flowing (3: 1 ratio) at a time.

<Performance evaluation>
Each S / C after the durability test was mounted on the 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 the A / F was feedback-controlled with the target of 14.1 and 15.1 was measured. The entering 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-based composite oxide of Example 2) in the lower coat and the NOx emission amount at the time of A / F switching. FIG. 7 shows the relationship between the amount of the OSC material (ceria-zirconia-based composite oxide of Example 2) added in the lower coat and the steady-state NOx purification rate.

From Table 3 and FIG. 6, the S / C using the ceria-zirconia-based composite oxide of the present invention significantly reduces the NOx emission amount at the time of A / F switching as compared with the one using other OSC materials. Was shown. Further, regarding the steady NOx purification ability and the NOx purification ability at the time of A / F switching, when the ceria-zirconia-based composite oxide of the present invention is contained in the lower layer coat, these performances are superior to those in the case where the upper layer coat is contained, and the mode running It has been shown to be beneficial in reducing NOx emissions at times. Further, from Tables 3, 6 and 7, when the amount of the ceria-zirconia composite oxide added to the lower coat of the present invention is 5 to 30 g / L, the low NOx emission amount at the time of A / F switching and the low NOx emission amount It was shown that both high steady NOx purification ability can be achieved.

<Underfloor 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% by weight), CeO ₂ (20% by weight), ZrO ₂ (44% by weight), Nd ₂ O ₃ (2% by weight), La ₂ O ₃ (2% by weight) and Y ₂ O ₃ (2% by weight) composite oxide (manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.)
AZ: Al ₂ O ₃ (30% by weight), ZrO ₂ (60% by weight), Nd ₂ O ₃ (2% by weight), La ₂ O ₃ (4% by weight) and Y ₂ O ₃ (4% by weight) Composite oxide (manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.)
OSC material:
-Ceria-zirconia-based composite oxide of Example 2 (Pr-added pyrochlore CZ)
-The ACZ-2
-Fluorite type ZC: CeO ₂ (21% by weight), ZrO ₂ (72% by weight), Nd ₂ O ₃ (5.3% by weight) and La ₂ O ₃ (1.7% by weight) fluorite type ZC Composite oxide (manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.)
Honeycomb base material: 875 cc (400 cell square wall thickness 4 mil) cordierite honeycomb base material

The UF / C was prepared as follows.

Comparative Example 16
(A) Preparation of lower layer coat Pd / ACZ-2 in which Pd is supported on ACZ-2 is prepared by an impregnation method using ACZ-2 and palladium nitrate, and a predetermined amount of Pd / ACZ-2, Al _{2 is prepared.} O ₃ and Al ₂ O ₃ based binders were added to distilled water with stirring and suspended to prepare slurry 1. The prepared slurry 1 was poured into a base material, unnecessary parts were blown off with a blower, and the wall surface of the base material was coated. The coating, with respect to the substrate capacity, Pd is 0.53g / L, _Al 2 _{O 3} is to 40g / L, ACZ-2 is contained 93 g / L. After coating, it was dried in a dryer kept at 120 ° C. for 2 hours and then fired in an electric furnace at 500 ° C. for 2 hours to prepare a lower coat.

(B) Preparation of upper layer coat Using AZ and rhodium nitrate, Rh / AZ in which Rh is supported on AZ is prepared by an impregnation method, 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 base material coated according to (a) above, unnecessary parts were blown off with a blower, and the undercoat of the base material wall surface was coated. The coating, with respect to the substrate capacitance, Rh is 0.4g / L, _Al 2 _{O 3} is to 35 g / L, AZ is included 33 g / L. After coating, it was dried in a dryer maintained at 120 ° C. for 2 hours and then fired in an electric furnace at 500 ° C. for 2 hours to obtain a UF / C in which the upper coat was formed on the lower 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 at 11 g / L, respectively, with respect to the substrate volume. , 20 g / L, 31 g / L, and 40 g / L were added so as to have a coating amount, and each UF / C was obtained in the same manner as in Comparative Example 16.

Example 17
The same as in Comparative Example 16 except that the ceria-zirconia-based composite oxide of Example 2 was added to the slurry 1 for forming the lower layer coat so as to have a coating amount of 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 volume.

Comparative Example 18
UF / C was obtained in the same manner as in Comparative Example 16 except that fluorite-type ZC 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 base material volume.

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

Durability tests were performed on the UF / Cs of Examples 13-17 and Comparative Examples 16-18 to evaluate their performance.

<Durability test>
Each UF / C of Example 13-17 and Comparative Example 16-18 was attached to the exhaust system of a V8 engine, and the exhaust gas of each atmosphere of stoichiometric and lean was exhausted for a certain period of time at a catalyst floor temperature of 950 ° C. for 50 hours. The durability test was carried out by repeatedly flowing (3: 1 ratio).

<Performance evaluation>
Each UF / C after the endurance test was mounted on the 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 the 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%. The temperature (T50-NOx) was measured to evaluate the catalytic activity.

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

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

Further, from FIG. 9, the steady HC purification rate increases according to the amount of the ceria-zirconia-based composite oxide of the present invention added in the upper coat, while the NOx purification ability at low temperature increases from FIG. The amount added decreases between 20 g / L and 30 g / L. Therefore, in the UF / C containing the ceria-zirconia-based composite oxide of the present invention in the uppermost layer of the catalyst coat layer, the addition amount thereof is 5 to 20 g in that both good steady HC purification ability and NOx purification ability can be achieved at the same time. The range of / L is preferable.

Claims (3)

An exhaust gas purification 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 was contained in the catalyst coat layer in an amount of 5 to 100 g / L with respect to the substrate volume.
The secondary particle size (D50) of the ceria-zirconia composite oxide is 3 to 7 μm.
Ceria-zirconia complex oxide contains praseodymium
The exhaust gas purification catalyst is the S of the exhaust gas purification catalyst system including the start-up catalyst (S / C) and the underfloor catalyst (UF / C) installed behind the S / C with respect to the flow direction of the exhaust gas. / C, the S / C has at least two catalyst coat layers, and the ceria-zirconia-based composite oxide is added to the maximum amount of the catalyst coat layer in an amount of 5 to 50 g / L with respect to the substrate capacity. comprising an upper layer, the exhaust gas purifying catalyst. An exhaust gas purification 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 was contained in the catalyst coat layer in an amount of 5 to 100 g / L with respect to the substrate volume.
The secondary particle size (D50) of the ceria-zirconia composite oxide is 3 to 7 μm.
Ceria-zirconia complex oxide contains praseodymium
The exhaust gas purification catalyst is the S of the exhaust gas purification catalyst system including the start-up catalyst (S / C) and the underfloor catalyst (UF / C) installed behind the S / C with respect to the flow direction of the exhaust gas. / C, the S / C has at least two catalyst coat layers, and the ceria-zirconia-based composite oxide is added to the maximum amount of the catalyst coat layer in an amount of 5 to 30 g / L with respect to the substrate capacity. comprising at least one layer other than the top layer, the exhaust gas purifying catalyst. An exhaust gas purification 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 was contained in the catalyst coat layer in an amount of 5 to 100 g / L with respect to the substrate volume.
The secondary particle size (D50) of the ceria-zirconia composite oxide is 3 to 7 μm.
Ceria-zirconia complex oxide contains praseodymium
The exhaust gas purification catalyst is a UF of an exhaust gas purification catalyst system including 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. / C, the UF / C has at least two catalyst coat layers, and the ceria-zirconia-based composite oxide is added to the maximum amount of the catalyst coat layer in an amount of 5 to 20 g / L with respect to the substrate volume. comprising an upper layer, the exhaust gas purifying catalyst.

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