WO2020031508A1 - Exhaust gas purification catalyst composition and exhaust gas purification catalyst using same - Google Patents

Abstract

This exhaust gas purification catalyst composition includes: a composite oxide that includes ceria, zirconia, and alumina; and a copper oxide that is supported by the composite oxide. In the composite oxide, the alumina content is not less than 30 mass% and the ceria content less than 50 mass%. With respect to 100 parts by mass of the composite oxide, the contained amount of the copper oxide is preferably 3-30 parts by mass. The copper oxide content is preferably 3-30 mass%. Preferably, the alumina content in the composite oxide is not less than 50 mass% and the ceria content in the composite oxide is not less than 2.5 mass%.

Description

Composition for exhaust gas purification catalyst and exhaust gas purification catalyst using the same

The present invention relates to an exhaust gas purifying catalyst composition and an exhaust gas purifying catalyst using the same.

BACKGROUND ART Conventionally, an exhaust gas purifying catalyst for purifying three components of carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NO _x ) discharged from an internal combustion engine such as a diesel engine or a gasoline engine has been proposed. These three components have been purified mainly by a composition for an exhaust gas purification catalyst in which a noble metal such as Pt, Rh or Pd is supported on a metal oxide. On the other hand, in recent years, for the purpose of reducing the amount of noble metal used and ultimately eliminating the noble metal, a composition in which copper oxide is supported on a metal oxide as a substitute for the noble metal has been proposed.

For example, Patent Literature 1 discloses a carrier comprising a composite metal oxide containing ceria, zirconia, and alumina, wherein the content of ceria in the composite metal oxide is 50% by mass or more, and a carrier supported on the carrier. A catalyst comprising copper oxide is described, and it is described as having excellent CO oxidation ability.

Patent Document 2 discloses a first purification member that contains a 3d transition element and does not contain a noble metal, and is disposed adjacent to the first purification member on both the upstream side and the downstream side in the exhaust gas passage direction with respect to the first purification member, An exhaust gas purifying catalyst including a second purifying member containing a noble metal is described. In Example 1 of Patent Document 2, the first purification member has Cu / θ-Al ₂ O ₃ , Cu / Ce _0.30 Zr _0.50 La _0.05 Y _0.05 Oxide, and HC and CO. It is described that the purification of the waste can be achieved.

JP 2011-183280 A JP 2013-107056 A

In the exhaust gas purification catalyst composition for the oxidation of copper was supported on a metal oxide in place of the noble metal as a catalyst active component, HC, particularly improvement of _the NO _x purification performance of the CO and NO _x is biggest challenge.
In this regard, not been investigated at all the configuration of Patent Document 1, and the exhaust gas purifying catalyst composition for improving the purification performance of the NO _x to 2.
Accordingly, an object of the present invention is to provide an exhaust gas purifying catalyst composition which can solve the above-mentioned problems, and an exhaust gas purifying catalyst using the same.

The present inventors have intensively studied the structure of an exhaust gas purification catalyst composition may have a purifying performance superior NO _x despite not using a noble metal. As a result, surprisingly, the copper oxide is be supported relative to the composite oxide containing ceria, zirconia and alumina with a controlled content of alumina and ceria in a specific range, it gives excellent _the NO _x purification performance Was found to be.

The present invention is based on the above findings, a composite oxide containing ceria, zirconia and alumina, and a composition for an exhaust gas purification catalyst comprising copper oxide supported on the composite oxide,
An object of the present invention is to provide a composition for an exhaust gas purifying catalyst, wherein the content of alumina in the composite oxide is 30% by mass or more and the content of ceria is less than 50% by mass.

The present invention also provides an exhaust gas purifying catalyst containing the composition for exhaust gas purifying catalyst.

Hereinafter, the present invention will be described based on preferred embodiments. The composition for an exhaust gas purifying catalyst of the present invention includes a composite oxide containing ceria, zirconia, and alumina (hereinafter, also referred to as “CZA composite oxide”), and copper oxide supported on the composite oxide. And

CZA composite oxide is a composite oxide containing cerium, zirconium and aluminum. In the CZA composite oxide, it is preferable that a part of alumina is present in a solid solution of ceria-zirconia in a solid solution. The fact that ceria and zirconia are in a solid solution can be confirmed by X-ray diffraction measurement based on whether or not a single phase derived from the ceria-zirconia solid solution has been formed. Further, when the CZA composite oxide is subjected to X-ray diffraction measurement, a diffraction peak of ceria, zirconia or a ceria-zirconia solid solution and a diffraction peak of alumina are generally observed separately. As a method for distinguishing the CZA composite oxide from the mixture of the alumina powder and the ceria-zirconia powder, for example, there is a method of judging from the result of the X-ray diffraction measurement as follows. First, when the sample was subjected to X-ray diffraction measurement, peaks derived from a solid solution of ceria-zirconia (2θ = three positions near 29 °, 34 °, and 48.5 °) were found to be a solid solution of ceria-zirconia. If a part of alumina dissolves in the solution and the peak shifts by about 2θ = 1 to 2 ° toward the low angle side, it can be determined that the sample is a CZA composite oxide. Alternatively, when a sample supporting Cu is subjected to a heat treatment at 950 ° C. for 4 hours and then subjected to X-ray diffraction measurement, peaks derived from a solid solution of ceria-zirconia (2θ = around 29 °, around 34 ° and Is present in three places around 48.5 °), but is separated into two or more peaks due to the phase separation of the solid solution of ceria-zirconia, it can be determined that the mixture is a mixture of alumina powder and ceria-zirconia powder, When one peak remains, it can be determined that the compound is a CZA composite oxide. It is preferable to use CuKα radiation as a radiation source for the X-ray diffraction measurement. Note that “near” related to the X-ray diffraction peak position means that it is within a range of ± 1.0 °.

In the present invention, is less than 50 mass% content of ceria in the CZA composite oxide, and is excellent in purification performance of the NO _x by supporting the copper oxide thereto. That is, a design in which the content of ceria in the CZA composite oxide is intentionally limited and copper oxide is supported on the design makes it possible to easily change the monovalent or divalent valence of copper in copper oxide. The reaction between ₂ O or O ₂ and HC or CO is more activated. Above all, _{by H 2} produced by the oxidation reaction of HC or CO by in _{H 2} O reacts with NO _x, considered to purification of the NO _x progresses.
On the other hand, when the content of ceria in the composite oxide is 50% by mass or more as in the technique described in Patent Document 1, due to its oxygen storage / release ability (hereinafter also referred to as “OSC”), Since CO and HC are exclusively oxidized by O ₂ and the oxidation reaction by H ₂ O is restricted, the desired NO _x purification performance referred to in the present application cannot be obtained.
The content of ceria in the CZA composite oxide here includes both the amount of ceria that does not form a solid solution and the amount of ceria that forms a solid solution.

In addition, by setting the content of alumina in the CZA composite oxide to 30% by mass or more, not only is it possible to suppress a decrease in the specific surface area of the CZA composite oxide, but also to improve the heat resistance of the composition for an exhaust gas purification catalyst. , The relative proportion of ceria in the CZA composite oxide can be reduced, and the NO _x purification performance can be improved not only after the heat endurance at 900 ° C. or higher but also before the heat endurance.

From the viewpoint of a more pronounced the more advantages more, especially from the viewpoint of enhancing _the NO _x purification performance in the previous thermal durability, the content of alumina in CZA composite oxide is preferably 30 mass% or more, more preferably 50 It is advantageous to set the amount to at least 70% by mass, more preferably at least 60% by mass, particularly preferably at least 70% by mass. This content is a value significantly higher than the content (about 11% by mass) of alumina in the CZA composite oxide in each example of Patent Document 1. Whereas the upper limit of the content of alumina in, from the viewpoint of particularly improving the _the NO _x purification performance in the previous thermal durability, preferably at most 98 mass%, more preferably not more than 95 wt%, 90 wt% or less Is more preferable.
The content of alumina in the CZA composite oxide is measured by the following method. First, the composition for exhaust gas purifying catalyst is dissolved to form a solution, and the amount of each element is measured by ICP-AES using the solution as a measurement object. Of the measured amounts of the respective elements, the amount of copper supported on the CZA composite oxide was determined, and the amounts of the remaining elements were converted to those oxides, and the total amount was 100, which was calculated as oxides. Calculate the percentage of the amount of aluminum.

Examples of the alumina contained in the CZA composite oxide include γ-alumina, β-alumina, δ-alumina, θ-alumina, α-alumina and the like, and any of them can be used. In particular, it is preferable to use θ-alumina because it has high thermal stability while maintaining the specific surface area of the composition for an exhaust gas purifying catalyst when combined with ceria-zirconia solid solution, ceria and / or zirconia.
Note that Patent Document 1 describes a composite metal oxide containing ceria, zirconia, and alumina. However, since alumina is dispersed on the nm scale, it is possible to confirm the crystal structure of alumina as described above. Can not. As a result, the thermal stability is poor, so that the performance after heat durability in the present invention is poor.

Exhaust gas purifying catalyst composition of the present invention have excellent _the NO _x purification performance thermal durability previous state, in particular in a state not receiving yet a and 4 hours of heating above 900 ° C.. Exhaust gas purifying catalyst composition of the present invention, in addition to it, even after receiving and 4 hours of heating 900 ° C. or higher, can maintain excellent _the NO _x purification performance. As one of the reasons, the present inventor thinks as follows. In the CZA composite oxide, as described above, it is preferable that a part of alumina is dissolved in a solid solution of ceria-zirconia, while the remaining part is formed of a solid solution of ceria, zirconia and ceria-zirconia. Does not dissolve. Therefore, the solid solution of ceria, zirconia, and / or ceria-zirconia, and the alumina that does not form a solid solution with each other, serve as diffusion barriers. Therefore, it is considered that aggregation of the same kind of oxides was suppressed and heat resistance was improved. In contrast, the composition for an exhaust gas purifying catalyst in which copper oxide is supported on a ceria-zirconia composite oxide having no alumina has no alumina serving as a diffusion barrier. likely to occur, catalytic activity area is reduced by phase separation of ceria and zirconia is caused by heating above 900 ° C., no sufficient _the nO _x purification performance.

Incidentally, in view of enhancing the _the NO _x purification performance more, from the viewpoint of particularly improving both _the NO _x purification performance of the front and rear heat durability, the content of ceria in the CZA composite oxide is 35% by mass or less, than 25 wt% Is more preferably 20% by mass or less, and particularly preferably 15% by mass or less. On the other hand, the lower limit of the content of the ceria is preferably from the viewpoint of enhancing _the NO _x purification performance in the state before the heat endurance is 1 mass% or more, further preferably 2.5 mass% or more, 5 mass % Is more preferable.
The ceria content in the CZA composite oxide is measured by a method similar to the method described above as a method for measuring the alumina content in the CZA composite oxide.
Further, in view of enhancing the _the NO _x purification performance more, from the viewpoint of particularly improving both _the NO _x purification performance of the front and rear heat durability, the weight ratio of alumina for ceria in CZA composite oxide (alumina / ceria) is preferably 5 or more, 7 or more is more preferable, and 10 or more is further preferable.

The content of zirconia in the CZA composite oxide, it is 1 mass% or more, from the viewpoint of enhancing the _the NO _x purification performance after thermal endurance, more preferably 2.5 mass% or more, 5% More preferably, it is the above. On the other hand, the upper limit of the amount of the zirconia, in view of particularly increasing the _the NO _x purification performance in the state before the heat endurance, preferably 35 wt% or less, still more preferably 25% by mass or less, 20 wt % Is more preferable.
The zirconia content in the CZA composite oxide is measured by a method similar to the method described above as a method for measuring the alumina content in the CZA composite oxide.

As can be seen from the above method of measuring the content, each of the above-mentioned contents of alumina, ceria, and zirconia includes both the amount constituting the solid solution and the amount not constituting the solid solution in the CZA composite oxide. I do.

Further, the content ratio (mass ratio) of ceria and zirconia in the CZA composite oxide is preferably 1 or more and 3 or less with respect to zirconia 1 from the viewpoint of thermal durability, and is preferably 1 or more and 2 or less. More preferably, there is. On the other hand, it is preferable that the zirconia against ceria 1 in terms of the NO _x purifying performance is 0.5 to 3, more preferably 0.5 to 2.

CZA composite oxide is preferable in that to contain a rare earth element other than cerium further enhance _the NO _x purification performance after thermal endurance. Rare earth elements other than cerium include scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. These rare earth elements can be contained in the CZA composite oxide as an oxide, for example. Two or more rare earth element oxides may be contained. The oxide of a rare earth element other than cerium may or may not form a solid solution with ceria-zirconia solid solution, ceria or zirconia. Whether or not an oxide of a rare earth element other than cerium forms a solid solution with a ceria-zirconia solid solution can be confirmed by X-ray diffraction measurement.

When the CZA composite oxide contains an oxide of a rare earth element other than cerium, the content of the oxide in the CZA composite oxide is such that copper oxide reacts with the oxide to lower the catalytic activity. From the viewpoint of preventing the above, the content is preferably 5% by mass or less, more preferably 3% by mass or less. On the other hand, from the viewpoint of securing thermal stability, the content is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more.
The amount of the rare earth oxide other than cerium includes both the amount of the rare earth oxide forming the solid solution and the amount of the rare earth oxide not forming the solid solution.

There is no particular limitation on the method for producing the CZA composite oxide, and it can be produced by, for example, a coprecipitation method, which is one of the liquid phase reaction methods. In the coprecipitation method, a basic substance containing an aqueous solution of aluminum is contained in an acidic solution containing a water-soluble salt of cerium, a water-soluble salt of zirconium, and a water-soluble salt of a rare earth element other than cerium as necessary. After adding to obtain a precipitate, the precipitate is dried, and calcined in the air. Examples of the water-soluble salts of rare earth elements other than cerium, zirconium, and cerium include nitrates, oxalates, acetates, ammine complexes, and chlorides. As the aqueous solution of aluminum, a sodium aluminate solution is used, and as the other basic substance, ammonia water or the like is used. The pH in the coprecipitation is controlled to be in the range of 6 to 10, and the precipitation temperature is controlled to be in the range of 48 to 80 ° C.

A surfactant may be further added to the obtained precipitate. In this case, the precipitate is sufficiently stirred with water or the like, washed, filtered, and dried. The surfactant can include any of polyvinyl alcohol (PVA), polyvinylamine, polyethylene glycol-200 (PEG-200), 2-propanol, ethanol, or a combination thereof.
The amount of the surfactant to be added is preferably in the range of 1% by mass to 30% by mass relative to the oxide equivalent of the metal constituting the water-soluble salt. The firing of the precipitate is preferably performed at a temperature of 600 ° C. or higher from the viewpoint of reliable formation of the CZA composite oxide. When the calcination temperature is 900 ° C. or higher, a CZA composite oxide containing θ-alumina as the alumina is easily obtained, which is preferable. The upper limit of the firing temperature is preferably 1100 ° C. or less from the viewpoint of ensuring the dispersibility of the ceria-zirconia solid solution and ceria. The firing time is preferably from 2 hours to 6 hours. As the firing atmosphere, for example, an oxygen-containing atmosphere such as the air, or an inert gas atmosphere such as a nitrogen gas and an argon gas can be used.

CZA composite oxide that the volume average particle diameter D ₅₀ is 3μm or more, preferably a point capable of increasing the gas diffusibility, and more preferably 7μm or more. On the other hand, the upper limit of D ₅₀ is preferably from the viewpoint of adhesion to the substrate when used as a catalyst layer is 60μm or less, more preferably 40μm or less. The preferred range of D ₅₀ D _{50 of,} and an exhaust gas purification catalyst composition for copper oxide-supporting composite oxide carrying copper oxide is the same range as the range described above as the preferred range of D ₅₀ of CZA composite oxide .

D ₅₀ of the CZA composite _oxide, D ₅₀ of the copper oxide-supporting composite oxide and D ₅₀ of the exhaust gas purifying catalyst _composition, can be measured, for example, as follows. That is, after using an automatic sample feeder (“Microtorac SDC” manufactured by Microtrac Bell Inc.) for a laser diffraction particle size distribution measuring apparatus, the CZA composite oxide was put into an aqueous solvent, and 30 W ultrasonic waves were irradiated for 360 seconds. It is measured using a laser diffraction scattering type particle size distribution meter (“Microtrac MT3000II” manufactured by Microtrac Bell). The measurement conditions are obtained as an average value of particle refraction index 1.5, particle shape true sphere, solvent refraction index 1.3, set zero 30 seconds, measurement time 30 seconds, twice measurement. Pure water is used as the aqueous solvent.

In the composition for an exhaust gas purifying catalyst of the present invention, copper oxide particles are supported on CZA composite oxide particles. Whether one particle carries another particle can be confirmed, for example, by measuring the particle size when observing the particle with a scanning electron microscope (hereinafter also referred to as “SEM”). For example, the average particle size of another particle present on the surface of one particle is preferably 10% or less, more preferably 3% or less, with respect to the average particle size of the one particle. It is particularly preferably 1% or less. The average particle diameter here is an average value of the maximum Feret diameter of 30 or more particles observed by SEM. The maximum Feret diameter is the maximum distance of a particle pattern between two parallel lines.
In the present invention, the copper oxide is supported on the CZA composite oxide, and is clearly different from the composite oxide of CZA and copper. With a composite oxide of CZA and copper as an exhaust gas purification catalyst composition, because the copper oxide and the exhaust gas component acting as an active hard contact, NO _x purifying performance is hardly exerted. On the other hand, copper oxide as in the present invention when it is made is supported in CZA composite oxide, and has excellent without _the NO _x purification performance inhibiting the catalytic performance as copper oxide.

It is preferred from the viewpoint of increasing the _the NO _x purification performance sufficiently CZA content of copper oxide in the composite oxide exhaust gas purifying catalyst composition of copper oxide supported on is 2.5% by mass or more, 4.5 It is more preferably at least 5.5% by mass, particularly preferably at least 5.5% by mass. On the other hand, the upper limit is preferably 25% by mass or less, from the viewpoint of securing the dispersibility of copper oxide and suppressing sintering, more preferably 15% by mass or less, and preferably 10% by mass or less. Is particularly preferred. Here, the amount of copper oxide is an amount in terms of CuO. From the same viewpoint, the amount of copper oxide is preferably 3 parts by mass or more and 30 parts by mass or less, more preferably 6 parts by mass or more and 15 parts by mass or less based on 100 parts by mass of the CZA composite oxide.
In the present invention, the form of copper oxide supported on the composite oxide may be either CuO or Cu ₂ O. Further, the preferable content of copper oxide in the exhaust gas purifying catalyst layer described later is also the same as the preferable range described above as the content of copper oxide in the composition for exhaust gas purifying catalyst.

The composition for an exhaust gas purifying catalyst may be composed of, for example, only a CZA composite oxide and copper oxide, but may also contain other components. As the component, for example, as those mainly serving as a carrier, inorganic porous materials such as TiO ₂ , SiO ₂ , zeolite, MgO, MgAl ₂ O ₄ , CeO ₂ , CeO ₂ -ZrO ₂ composite oxide, etc. OSC materials, alkaline earth metal compounds such as Ba, Sr, and Mg, and alumina sol and zirconia sol as binders. Note that these components may also carry copper oxide.

From the viewpoint of obtaining excellent _the NO _x purification performance and heat resistance, the proportion of CZA composite oxide occupied in the exhaust gas purifying catalyst composition is preferably not more than 60 wt% to 90 wt%, 70 wt% or more 87 It is more preferable that the content is not more than mass%.

In addition, the content of the CZA composite oxide in the composition for an exhaust gas purifying catalyst can be measured by the following method. That is, the composition for exhaust gas purifying catalyst is dissolved to form a solution, and the amount of each element is measured by ICP-AES using the solution as a measurement object. Next, an analysis field including only the CZA composite oxide supporting copper at a specific magnification is selected, and the element analysis is performed by the EDX. The difference between the amounts of the respective elements obtained from the ICP-AES and the results of the elemental analysis obtained by the EDX can be distinguished from the additives other than the CZA composite oxide such as the binder component. Can be specified.

The specific surface area of the CZA composite oxide in the composition for exhaust gas purifying catalyst is preferably 50 m ² / g or more before heat endurance, because it is easy to obtain a desired amount of copper oxide and the dispersibility of copper oxide. less in order to increase sufficiently _the NO _x purification performance is secured, more preferably ^{60 m} 2 / g or more, and particularly preferably ^70m 2 / g or more. On the other hand, it is preferable from the viewpoint of securing the suppressing _the NO _x purification performance aggregation of copper oxide by heat durability, more preferably at most 140 m ² / g and the upper limit is not more than 150m ² / g, 130m ² / G or less is particularly preferred.
On the other hand, after heat durability, it is preferably at least 15 m ² / g, more preferably at least 20 m ² / g. The upper limit is preferably 140 m ² / g or less, more preferably 130 m ² / g or less. For example, the heat durability is preferably performed in the atmosphere at 900 ° C. for 4 hours, and then in an inert atmosphere such as nitrogen or argon at 950 ° C. for 4 hours. Under these conditions, the maintenance ratio of the specific surface area of the CZA composite oxide in the composition for exhaust gas purification catalyst (= specific surface area after heat endurance / specific surface area before heat endurance × 100) is preferably 25% or more. , 35% or more. The specific surface area is measured by the BET three-point method. Specifically, it is measured by the method described in Examples below. The specific surface area and the maintenance ratio of the CZA composite oxide can be determined by measuring the CZA composite oxide supporting copper oxide.

CZA composite oxide and the exhaust gas purification catalyst composition having a supported copper oxide to the composite oxide, taking advantage of its excellent _the NO _x purification performance can be suitably used as an exhaust gas purifying catalyst. For example, in the exhaust gas purifying catalyst having a catalyst layer formed on the substrate and the substrate surface, a catalyst layer that is formed by the exhaust gas purifying catalyst composition, the exhaust gas purifying catalyst having an excellent _the NO _x purification performance Obtainable.

The shape of the substrate is not particularly limited, but is generally a honeycomb shape, a plate, a pellet, or the like, and is preferably a honeycomb. Examples of the material of such a substrate include alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ -2SiO ₂ ), cordierite (2MgO-2Al ₂ O ₃ -5SiO ₂ ), and aluminum titanate. Ceramic materials such as (Al ₂ TiO ₅ ) and silicon carbide (SiC) and metal materials such as stainless steel can be used.

A slurry containing the water-soluble copper salt and the CZA composite oxide was applied to the surface of the substrate, dried, and calcined, whereby a catalyst layer composed of the exhaust gas-purifying catalyst composition of the present invention was formed on the substrate. An exhaust gas purifying catalyst can be obtained. For example, a CZA composite oxide and, if necessary, other components are added to an aqueous solution containing a water-soluble salt of copper to prepare a slurry, and the slurry is applied to a substrate, dried, and fired. Alternatively, an exhaust gas purifying catalyst may be formed. From the viewpoint of increasing the catalytic activity of the obtained exhaust gas purifying catalyst, the temperature at which the substrate coated with the slurry is fired is preferably 300 ° C to 800 ° C, more preferably 400 ° C to 600 ° C. The firing time is preferably 0.5 hours to 10 hours, more preferably 1 hour to 3 hours. The firing can be performed, for example, in the atmosphere.

The amount of the composition for an exhaust gas purifying catalyst in the exhaust gas purifying catalyst is preferably 50 g / L or more when the base material is a honeycomb shape, from the viewpoint of obtaining heat resistance and exhaust gas purifying performance at a low temperature, and more preferably 70 g / L or more. More preferably, it is particularly preferably 85 g / L or more. On the other hand, it is preferably 220 g / L or less from the viewpoint of obtaining a suitable low-temperature activity while preventing a decrease in back pressure, more preferably 200 g / L or less, and particularly preferably 180 g / L or less. .
The amount of the composition for an exhaust gas purifying catalyst in the exhaust gas purifying catalyst referred to herein is an amount based on the volume based on the outer shape of the substrate, including all spaces in the substrate as a part of the volume of the substrate. .

As described above, the exhaust gas purifying catalyst composition of the present invention, and the exhaust gas purifying catalyst using the same exhibit excellent _the NO _x purification performance in previous thermal endurance. Moreover, even when exposed to temperatures higher than 900 ° C. exhibits stable _the NO _x purification catalyst performance. Such an exhaust gas purifying catalyst composition and an exhaust gas purifying catalyst can exhibit stable and high exhaust gas purifying performance when used in an internal combustion engine using a fossil fuel as a power source, such as a gasoline engine or a diesel engine. In particular, with respect to two-wheeled motor vehicle fluctuation region of the exhaust gas as compared with four-wheeled vehicles because it closer to the rich side (lambda> 1), in _the NO _x purification reaction is performed friendly environment. Therefore, the composition for an exhaust gas purifying catalyst of the present invention is suitably used particularly for motorcycles.

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited to such embodiments. Drying and firing in the production of the composition for exhaust gas purifying catalyst and the exhaust gas purifying catalyst were all performed in the air. The specific surface area was determined by a BET three-point method using a specific surface area / pore distribution measuring device (model number: QUADRASORB @ SI) manufactured by Cantachrome. Helium was used as a measurement gas.

<Example 1>
(1) Manufacture of slurry for forming exhaust gas purification catalyst Using cerium nitrate hexahydrate, zirconyl nitrate dihydrate, yttrium nitrate aqueous solution and lanthanum nitrate aqueous solution, the total of cerium nitrate, zirconyl nitrate, yttrium nitrate and lanthanum nitrate was used. A nitrate aqueous solution having a concentration of 0.1 mol / L was formed. This nitrate aqueous solution has a composition in which the oxide-converted mass ratio of cerium nitrate, zirconyl nitrate, yttrium nitrate, and lanthanum nitrate is CeO ₂ : ZrO ₂ : Y ₂ O ₃ : La ₂ O ₃ = 33: 25: 1: 1. Had. Next, an aqueous solution of sodium aluminate was prepared, and the aqueous solution of sodium aluminate was dropped into this aqueous solution of nitrate to form a slurry having a pH of 7 at a temperature of 75 ° C. The oxide-equivalent mass ratio of aluminum in the slurry to the mixed metal composed of Ce, Zr, Y and La was 40:60.
After precipitation, the temperature was raised to 90 ° C, the slurry was aged for 30 minutes, and then cooled to 40 ° C. Next, PEG-200 as a surfactant was added to the slurry at a ratio of 30% by mass based on the total mass of the mixed metal in terms of oxide. The slurry was stirred for 1 hour, then collected and washed with deionized water. The obtained wet solid was dried in an oven at 120 ° C. for about 12 hours and sieved to obtain a dry powder. Next, the obtained powder was fired at 1000 ° C. for 4 hours to obtain a CZA composite oxide. The amounts of Al ₂ O ₃ , ZrO ₂ , CeO ₂ , La ₂ O ₃ and Y ₂ O _{3 in} the obtained CZA composite oxide were as shown in Table 1. The volume average particle diameter D ₅₀ of the resulting CZA composite oxide was measured by the above method, it was 10 [mu] m. Further, X-ray diffraction measurement of the CZA composite oxide confirmed that alumina was θ-alumina. Further, in the X-ray diffraction measurement of the above-mentioned source, it was confirmed that the diffraction peak of the ceria-zirconia solid solution was shifted to the lower angle side, and that a part of alumina was dissolved in the ceria-zirconia solid solution. confirmed. Further, it was confirmed by X-ray diffraction measurement that ZrO ₂ , CeO ₂ , La ₂ O ₃ and Y ₂ O ₃ formed a solid solution.
Next, the powder of the CZA composite oxide obtained in the above (1) is added to an aqueous solution obtained by dissolving copper (II) nitrate trihydrate in ion-exchanged water and stirred, and then a zirconia binder is added. A slurry for forming an exhaust gas purifying catalyst was obtained. The composition of the slurry for forming an exhaust gas purifying catalyst has a composition ratio of 6.0% by mass of copper oxide, 85.5% by mass of CZA composite oxide, and 8.5% by mass of zirconia when the composition for an exhaust gas purifying catalyst is used. Was prepared as follows.

(2) Production of Exhaust Gas Purifying Catalyst The slurry for forming an exhaust gas purifying catalyst prepared in the above (1) was prepared using a honeycomb substrate made of stainless steel (manufactured by Koshi Giken Kogyo Co., Ltd., diameter 40 mm, axial length 60 mm, cell number 300 cpsi, volume 0. 0754 L), and excess slurry was blown off. Next, after drying by directing hot air at 70 ° C. directly onto the surface to which the composition is applied, baking is performed at 450 ° C. for 1 hour to remove nitrate, and an exhaust gas purifying catalyst in which a catalyst layer is formed on a stainless steel honeycomb substrate. I got
The catalyst layer was composed of the exhaust gas-purifying catalyst composition having the above composition, and was mainly composed of a powder in which copper oxide was supported on a CZA composite oxide. The amount of the catalyst layer was 165 g / L based on the volume of the substrate.
Incidentally, as a sample for D ₅₀ measurements taken out by crushing the part of the catalyst obtained in Example 1 from the honeycomb base material, the resulting catalyst powder sample, and the method of measuring the D ₅₀ of the CZA composite oxide When _D50 was measured by the same method, it was as shown in Table 1.
Furthermore, the obtained catalyst powder sample was durable under the conditions described below. The specific surface area and the maintenance ratio of the specific surface area of the catalyst powder samples before and after the durability test were measured by the above-described method. Table 1 shows the results.

<Examples 2 to 4>
The amounts of cerium nitrate hexahydrate, zirconyl nitrate dihydrate, lanthanum nitrate aqueous solution, yttrium nitrate aqueous solution, and aluminum hydroxide used were determined based on the amounts of Al ₂ O ₃ , ZrO ₂ , CeO ₂ , and La _{2 in the} obtained CZA composite oxide. A composition for an exhaust gas purifying catalyst and an exhaust gas purifying catalyst were obtained in the same manner as in Example 1 except that the amounts of O ₃ and Y ₂ O ₃ were changed so as to be the values shown in Table 1.
To obtain a catalyst powder sample as described in Example 1, it was measured for its D _50, were as shown in Table 1.
Table 1 shows the results of measuring the specific surface area and the retention rate of the specific surface area of the catalyst powder samples before and after durability, as in Example 1.

<Example 5>
The particle size D ₅₀ of the CZA composite oxide except for using the 24μm was obtained an exhaust gas purifying catalyst composition, and the exhaust gas purifying catalyst in the same manner as in Example 3. To obtain a catalyst powder sample as described in Example 1, was measured in the D ₅₀ in the same manner as in Example 1, it was as shown in Table 1.
Table 1 shows the results of measuring the specific surface area and the retention rate of the specific surface area of the catalyst powder samples before and after durability, as in Example 1.

<Comparative Example 1>
In Example 1, a commercially available ceria-zirconia composite oxide was used instead of the CZA composite oxide (the amounts of ZrO ₂ and CeO ₂ are as shown in Table 1). Except for these, in the same manner as in Example 1, a composition for an exhaust gas purifying catalyst and an exhaust gas purifying catalyst were obtained.
The compositions of the exhaust gas purifying catalyst composition and the catalyst layer were 6.0% by mass of copper oxide, 85.5% by mass of ceria-zirconia composite oxide, and 8.5% by mass of zirconia. To obtain a catalyst powder sample as described in Example 1, it was measured for its D _50, were as shown in Table 1.
Table 1 shows the results of measuring the specific surface area and the retention rate of the specific surface area of the catalyst powder samples before and after durability, as in Example 1.

<Comparative Example 2>
In Example 1, a commercially available La-stabilized θ-alumina was used in place of the CZA composite oxide (the amounts of Al ₂ O ₃ and La ₂ O ₃ are as shown in Table 1). Except for these, in the same manner as in Example 1, a composition for an exhaust gas purifying catalyst and an exhaust gas purifying catalyst were obtained.
The compositions of the exhaust gas-purifying catalyst composition and the catalyst layer were 6.0% by mass of copper oxide, 85.5% by mass of alumina, and 8.5% by mass of zirconia. To obtain a catalyst powder sample as described in Example 1, it was measured for its D _50, were as shown in Table 1.
Table 1 shows the results of measuring the specific surface area and the retention rate of the specific surface area of the catalyst powder samples before and after durability, as in Example 1.

[Evaluation]
The exhaust gas purifying catalysts of Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to a durability test under the following conditions.
<Durability conditions>
Firing at 900 ° C. in the air for 4 hours, and then firing at 950 ° C. for 4 hours in a nitrogen atmosphere.

Wherein the exhaust gas purifying catalyst before and after the durability test, performed measurements of T50 and η400 of the NO _x in the following conditions to evaluate the purification performance of the NO _x. Table 2 shows the results.
<T50, η400 measurement conditions>
The exhaust gas purifying catalyst was disposed in a gas flow path, and a simulated exhaust gas having the following composition was passed. By gradually increasing the gas temperature flowing into the exhaust purification catalyst from room temperature to obtain the amount of NO _x contained in exhaust gas that has passed through the catalyst, A: NO _x detection amount of the catalyst unestablished, B: after catalyst installation NO _x when the detected amount was determined _the NO _x purification rate by the following equation.
NO _x purification rate (%) = (AB) / A × 100
_The NO _x purification rate is calculated by defining the gas temperature of the catalyst when it reaches 50% and light-off temperature T50. η400 performs the same measurement as T50, is _the NO _x purification rate when the temperature constant at 400 ° C. The exhaust gas flowing into the device. T50 means the better the lower the _the NO _x purification performance, Ita400 means the better the higher _the NO _x purification performance.
Mock gas (composition volume _{basis): CO: 1.25%, C} 3 H 6: 1740ppmC, NO: 2450ppm, O 2: 0.6%, CO 2: 14%, H 2 O: 10%, N ₂ : Residual gas flow rate: 25 L / min
-Temperature rise rate: 20 ° C / min

As shown in Table 2, each example, T50 is 346 ° C. or less before the durability, in η400 91% or more, shows excellent _the NO _x purification performance. On the other hand, in Comparative Example 1 in which copper oxide was supported on a ceria-zirconia composite oxide that was not a CZA composite oxide, and in Comparative Example 2 in which copper oxide was supported on θ-alumina, higher than in example inferior in _the NO _x purification performance. Further, in each example, T50 is 378 ° C. or less even after the durability, and high purification performance is maintained. In contrast, Comparative Example 1 is significantly higher than the embodiments T50, poor _the NO _x purification performance after endurance.

According to the present invention, an exhaust gas purifying catalyst composition is excellent in purification performance of the NO _x and exhaust gas purification catalyst is provided without using a noble metal.

Claims (7)

1. A composite oxide containing ceria, zirconia and alumina, and a composition for an exhaust gas purification catalyst having copper oxide supported on the composite oxide,
   A composition for an exhaust gas purifying catalyst, wherein the content of alumina in the composite oxide is 30% by mass or more and the content of ceria is less than 50% by mass.
2. The composition for an exhaust gas purifying catalyst according to claim 1, wherein the content of the copper oxide is 3 parts by mass or more and 30 parts by mass or less based on 100 parts by mass of the composite oxide.
3. The composition for an exhaust gas purifying catalyst according to claim 1 or 2, wherein the content of alumina in the composite oxide is 50% by mass or more, and the content of ceria in the composite oxide is 2.5% by mass or more. object.
4. The composition for an exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the content of zirconia in the composite oxide is 1% by mass or more and 35% by mass or less.
5. The composition for an exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein the alumina in the composite oxide is θ-alumina.
6. The volume average particle diameter D ₅₀ is 3μm or more 60μm or less, according to claim 1 to an exhaust gas purifying catalyst composition according to any one of 5.
7. An exhaust gas purifying catalyst comprising the composition for an exhaust gas purifying catalyst according to any one of claims 1 to 5.