JP6769839B2 - Three-way catalyst for exhaust gas purification, its manufacturing method, and catalyst converter for exhaust gas purification - Google Patents

Description

The present invention relates to an exhaust gas purification catalyst in which Pd catalyst particles are supported on specific base material particles, a method for producing the same, and an exhaust gas purification catalyst converter.

Platinum group elements such as ruthenium, rhodium, palladium, osmium, iridium, and platinum (NOx) in the purification of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from internal combustion engines such as automobiles. A three-way catalyst (TWC: Three-Way Catalyst) using PGM: Platinum Group Metal) as a catalytically active ingredient is widely used. Conventionally, as a three-way catalyst, a catalyst having a carrier (base material particles) made of a metal oxide such as alumina, zirconia, and ceria, and catalyst particles such as Pt supported on the carrier is widely known. ..

In this type of exhaust gas purification catalyst, a catalyst metal is supported on a carrier in the form of fine particles in order to reduce the amount of relatively expensive PGM used and to secure high catalytic activity. However, when the catalyst metal particles on the carrier are exposed to a high temperature environment, the particles grow by sintering with each other, which causes a problem that the catalytically active sites are significantly reduced.

As a technique for suppressing the synterling of such a catalyst metal, for example, in Patent Document 1, a mixture in which primary particles of Al ₂ O ₃ particles and particles of a predetermined metal oxide are mixed in nano-order is used as a carrier. A catalyst for purifying exhaust gas in which a platinum group element is supported on a carrier is disclosed. According to this technique, since the primary particles of Al ₂ O _{3 and} the primary particles of a predetermined metal oxide are interposed between the respective particles, the progress of grain growth of the primary particles of the single oxide is suppressed. As a result, it is said that the decrease in the surface area and the pore volume is sufficiently suppressed, and the dispersibility of the catalyst component to be supported can be sufficiently maintained.

Further, for example, Patent Document 2 discloses an exhaust gas purification oxidation catalyst having a carrier made of AZT oxide or AZ oxide and a noble metal that catalyzes the oxidation of carbon monoxide supported on the carrier. .. According to this technique, at a base point on the surface of a carrier composed of AZT oxide or AZ oxide, that is, at the site of an atom or atomic group exhibiting basic properties, an atom of a noble metal such as palladium or platinum via an oxygen atom. Since (ions) are firmly fixed (supported), it is said that the effect of suppressing syntaring is high and the grain growth of noble metals can be suppressed.

However, the exhaust gas purification catalysts of Patent Documents 1 and 2 are exhaust gas purification catalysts for diesel engines that use Al ₂ O ₃ as a base material particle, and are used for internal combustion engines such as gasoline engines that generate higher temperature exhaust gas. There is a problem that the heat resistance is insufficient and the catalyst performance is rapidly lowered.

On the other hand, as a three-way catalyst with improved heat resistance, Patent Document 3 states that the palladium content is in the range of 0.05 to 7% by weight and the Pr / (Zr + Pr) atomic ratio is 0.05 to 0.6. Zr _α Pr _β Pd _γ O _2-δ (where α + β + γ = 1.000, where δ is a value determined to satisfy the charge neutrality condition.) Exhaust gas purification three-way catalyst composed of solid solution components Is disclosed.

On the other hand, Patent Documents 4 and 5 describe ceria-doped with rare earth elements such as yttrium, lantern, neodymium, praseodymium and gadolinium as an auxiliary catalyst (oxygen storage material) having an oxygen storage capacity (OSC: Oxygen Storage Capacity). Zirconia-based metal oxides are disclosed.

International Publication No. 2012/121085 Pamphlet International Publication No. 2012/137930 Pamphlet Japanese Unexamined Patent Publication No. 2013-166130 International Publication No. 2011/083157 Pamphlet International Publication No. 2010/09737 Pamphlet

However, the exhaust gas purification three-way catalyst described in Patent Document 3 requires heat treatment in the air at 800 to 1100 ° C. for several tens of hours in order to obtain a solid solution having a special crystal structure, and is inferior in productivity. Further, Patent Documents 4 and 5 are limited to the disclosure of ceria-zirconia-based metal oxide as an oxygen storage material.

The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a three-way catalyst for exhaust gas purification, a method for producing the same, a catalyst converter for exhaust gas purification, etc., which have a large palladium surface area, excellent heat resistance and ternary purification performance, and are easy to manufacture and excellent in productivity. To provide.

The present inventors have diligently studied to solve the above problems. As a result, they have found that the above problems can be solved by adopting a new structure in which Pd catalyst particles are supported on specific base material particles, and have completed the present invention.

That is, the present invention provides various specific aspects shown below.
(1) Nd solid-soluble zirconia-based composite oxide containing Nd and Zr as constituent metal elements in the following mass ratios: ZrO ₂ 50 to 75 mass%; Nd ₂ O ₃ 25 to 50 mass%; A three-way catalyst for purifying exhaust gas, which comprises at least the base material particles and Pd catalyst particles supported on the base material particles.
(2) The three-way catalyst for exhaust gas purification according to (1), wherein the Pd catalyst particles are contained in an amount of 0.1 to 10% by mass in terms of metallic palladium.
(3) The Nd solid-dissolved zirconia-based composite oxide contains at least one or more rare earth elements selected from the group consisting of yttrium, scandium, lanthanum, and praseodymium as constituent metal elements in a total of 0 to 20 mass in terms of oxide. % The ternary catalyst for purifying exhaust gas according to (1) or (2).
(4) The Nd solid solution zirconia-based composite oxide contains La as a constituent metal element in the following mass ratio: La ₂ O _{30 to} 18 mass% in terms of oxide; (1) to (3). The three-way catalyst for exhaust gas purification according to any one item.
(5) The three-way catalyst for exhaust gas purification according to any one of (1) to (4), wherein the base metal particles have an average particle diameter D ₅₀ of 1 to 100 μm.
(6) The three-way catalyst for exhaust gas purification according to any one of (1) to (5), wherein the palladium surface area calculated by the carbon monoxide gas pulse adsorption method is 15 to 30 (m ² / Pd_g).
(7) The three-way catalyst for exhaust gas purification according to any one of (1) to (6), which has a BET specific surface area of 10 to 50 m ² / g.

(8) Nd solid-soluble zirconia-based composite oxide containing Nd and Zr as constituent metal elements in the following mass ratios: ZrO ₂ 50 to 75 mass%; Nd ₂ O ₃ 25 to 50 mass%; A step of preparing the base material particles, a step of applying an aqueous solution containing at least Pd ions to the surface of the base material particles, and a heat treatment or chemical treatment of the treated base material particles to surface the base material particles. A method for producing a ternary catalyst for purifying exhaust gas, which comprises at least a step of supporting Pd catalyst particles.
(9) A catalyst carrier, an oxygen storage layer provided on the catalyst carrier, and a catalyst layer provided on the oxygen storage layer are provided at least, and the catalyst layer is any of (1) to (7). A catalyst converter for exhaust gas purification, which comprises the three-way catalyst for exhaust gas purification according to the above item.

According to the present invention, a three-way catalyst for exhaust gas purification, a method for producing the same, a catalyst converter for exhaust gas purification, and the like, which have a large surface area of palladium, excellent heat resistance and ternary purification performance, are easy to manufacture, and are excellent in productivity, are realized. can do. The exhaust gas purification catalyst of the present invention is a catalyst particle having a composite structure in which a large number of minute active points (Pd catalyst particles) are supported on a base material particle of an Nd solid-dissolved zirconia-based composite oxide, and the composition and structure thereof. Based on the above, it can be particularly preferably used as a three-way catalyst (TWC: Tree Way Catalyst) that reduces NOx, CO, HC and the like in the exhaust gas. The exhaust gas purification catalyst or the like of the present invention can be mounted on a catalyst converter directly under the engine, a catalyst converter directly under the engine in a tandem arrangement, or the like, whereby the canning cost can be reduced.

It is a scattered electron image (ZC image) of STEM of the three-way catalyst for exhaust gas purification (sample for performance evaluation) of Example 7.

Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples for explaining the present invention, and the present invention is not limited thereto. In the present specification, for example, the notation of the numerical range of " 1 to 100 " includes both the upper limit value " 100 " and the lower limit value " 1 ". The same applies to the notation of other numerical ranges.

The three-way catalyst for exhaust gas purification of the present embodiment contains at least the base material particles of the Nd solid-soluble zirconia-based composite oxide having a specific composition and the Pd catalyst particles supported on the base material particles. This Nd solid-dissolved zirconia-based composite oxide contains at least neodymium (Nd), zirconium (Zr), and oxygen (O) as constituent elements, and Nd and Zr have the following mass in terms of oxide. It is contained in proportion.
ZrO ₂ : 50-75% by mass
Nd ₂ O ₃ : 25 to 50% by mass

By using the base material particles of the Nd solid-soluble zirconia-based composite oxide having such a composition, it is possible to realize a three-way catalyst for exhaust gas purification in which fine Pd catalyst particles are supported on the base material particles in a highly dispersed manner. Can be done. Hereinafter, the estimation action of the three-way catalyst for exhaust gas purification of the present embodiment will be described.

As mentioned earlier, in this type of catalyst, when exposed to a high temperature environment, the catalyst particles on the base metal particles are sintered to grow, which significantly reduces the catalytically active sites and the catalyst. It is known that performance is reduced. On the other hand, in the three-way catalyst for exhaust gas purification of the present embodiment, when the external environment is switched from the reducing atmosphere to the oxidizing atmosphere, the Nd and Pd catalyst particles contained in the base material particles become a composite oxide or the like. When a solid solution is formed and the external environment is switched from an oxidizing atmosphere to a reducing atmosphere, fine Pd catalyst particles are redispersed on the base material particles from the composite oxide or the solid solution. That is, in the present embodiment, the Pd catalyst particles are used as so-called PdO / Nd ₂ O ₃ mixed oxides, and fine Pd catalyst particles are highly dispersed on the base material particles in response to changes in the external environment. It is designed to be carried. Further, since the zirconia-based composite oxide having relatively excellent heat resistance is used as the base material particles, the heat resistance of the catalyst itself is also enhanced. As a result of these combinations, it is presumed that a three-way catalyst for exhaust gas purification, which has excellent heat resistance and three-way purification performance, has been realized. However, the action is not limited to these.

As described above, the base material particles and the Pd catalyst particles may be confirmed at least in a reducing atmosphere, and the properties of the Pd catalyst particles in an oxidizing atmosphere or a stoichiometric atmosphere are not particularly limited. Here, in the present specification, the reducing atmosphere means a state of being allowed to stand at 400 ° C. for 0.5 hours or more in a hydrogen gas atmosphere. The Pd catalyst particles can be confirmed by using, for example, a scanning transmission electron microscope (STEM) having a magnification of 1 million times, HD-2000 manufactured by Hitachi High-Technologies Corporation, or the like. Hereinafter, each component will be described in detail.

The mass ratio of Zr contained in the Nd solid-soluble zirconia-based composite oxide is preferably 50 to 74% by mass, more preferably 50 to 70% by mass, and further preferably 50 to 50 to 74% by mass in terms of oxide (ZrO ₂ ). It is 65% by mass. Since zirconia has excellent heat resistance, it is suitable as a base material for an exhaust gas purification catalyst used in a high temperature environment. Further, the zirconia-based composite oxide has an advantage that the formation of compounds of La and Nd to be co-supported is suppressed as compared with alumina.

On the other hand, the mass ratio of Nd contained in the Nd solid-dissolved zirconia-based composite oxide is preferably 26 to 50% by mass, more preferably 30 to 50% by mass, and further, in terms of oxide (Nd ₂ O ₃ ). It is preferably 35 to 50% by mass. By using the zirconia-based composite oxide in which Nd, which is a rare earth element, is dissolved in this way, the heat resistance of zirconia tends to be improved and the exhaust gas purification performance tends to be improved. Further, the dispersibility of the supported Pd catalyst particles tends to be improved.

Here, the Nd solid solution zirconia-based composite oxide may contain other elements in addition to the above-mentioned constituent elements. For example, it contains rare earth elements such as ytterbium, cerium, scandium, lantern, placeodim, promethium, samarium, urobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, as long as the effects of the present invention are not significantly impaired. You may be. These rare earth elements may be used alone or in combination of two or more.

Among these, yttrium (Y), scandium (Sc), lanthanum (La), and praseodymium (Pr) can be used in place of Nd doped in the zirconia-based composite oxide, and are preferable. At this time, the Nd solid-dissolved zirconia-based composite oxide preferably contains yttrium, scandium, lanthanum, and praseodymium in a total of 0 to 18% by mass, more preferably 0 to 15 in terms of oxides. It is by mass, more preferably 0 to 10% by mass.

A preferred embodiment is an Nd-La solid-dissolved zirconia-based composite oxide containing at least Nd, Zr, La and O as constituent elements, wherein Nd, Zr and La have the following mass ratios in terms of oxide. Those contained in are mentioned.
ZrO ₂ : 50-75% by mass
Nd ₂ O ₃ : 25 to 50% by mass
La ₂ O ₃ : 0 to 18% by mass

On the other hand, from the viewpoint of maintaining the higher effect of the present invention, among the above-mentioned rare earth elements, cerium, promethium, samarium, urobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium are dissolved in Nd. It is preferable that it is not substantially contained in the zirconia-based composite oxide. Here, substantially not contained means that the mass ratio in terms of these oxides is 0 to 5% by mass with respect to the Nd solid-soluble zirconia-based composite oxide, and more preferably 0 to 3. It is by mass%, more preferably 0 to 1% by mass.

The Nd solid solution zirconia-based composite oxide may contain hafnium (Hf), which is usually contained in about 1 to 2% by mass in the zirconia ore, as an unavoidable impurity. Here, the total amount of unavoidable impurities excluding hafnium is preferably 0.3% by mass or less. Further, in the Nd solid-dissolved zirconia-based composite oxide, a part of zirconium may be replaced with an alkali metal element, an alkaline earth metal element, or the like as long as the effect of the present invention is not significantly impaired. Furthermore, the Nd solid-dissolved zirconia-based composite oxide contains transition metal elements such as iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu) as long as the effects of the present invention are not significantly impaired. It may be contained.

The base material particles of the Nd solid solution zirconia-based composite oxide having the above-mentioned specific composition preferably have an average particle diameter D ₅₀ of 1 to 100 μm, more preferably 1.5 to 100, from the viewpoint of maintaining a large specific surface area. It is 60 μm, more preferably 2 to 30 μm. In the present specification, the average particle size D ₅₀ means a median diameter measured by a laser diffraction type particle size distribution measuring device (for example, a laser diffraction type particle size distribution measuring device SALD-3100 manufactured by Shimadzu Corporation). ..

As the mother particles, various grades of commercially available products can be used. Further, the Nd solid solution zirconia-based composite oxide having the above-mentioned composition can also be produced by a method known in the art. The method for producing the Nd solid solution zirconia-based composite oxide is not particularly limited, but the coprecipitation method or the alkoxide method is preferable.

As a coprecipitation method, for example, an alkaline substance is added to an aqueous solution obtained by mixing a zirconium salt, a neodymium salt and a rare earth metal element to be blended as necessary at a predetermined chemical quantitative ratio, and the mixture is hydrolyzed or the precursor is coprecipitated. A method of submerging and firing the hydrolysis product or coprecipitate thereof is preferable. The types of various salts used here are not particularly limited. In general, hydrochloride, oxy hydrochloride, nitrate, oxynitrate, carbonate, phosphate, acetate, oxalate, citrate and the like are preferable. Further, the type of alkaline substance is not particularly limited. Generally, an aqueous ammonia solution is preferable. As the alkoxide method, for example, a production method in which a mixture of zirconium alkoxide, neodymium alkoxide, and a rare earth metal element to be blended as needed is hydrolyzed at a predetermined chemical quantity theory ratio and then fired is preferable. The type of alkoxide used here is not particularly limited. Generally, methoxide, ethoxide, propoxide, isopropoxide, butoxide, and ethylene oxide adducts thereof are preferable. Further, the rare earth metal element may be blended as a metal alkoxide or as various salts described above.

The firing conditions may be according to a conventional method and are not particularly limited. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and a neutral atmosphere. The calcination temperature and treatment time vary depending on the desired composition of the solid solution zirconia-based composite oxide and its stoichiometric ratio, but from the viewpoint of productivity and the like, generally, 1 at 150 ° C to 1300 ° C. It is preferably ~ 12 hours, more preferably 350 ° C. to 800 ° C. for 2 to 4 hours. Prior to high-temperature firing, it is preferable to perform vacuum drying using a vacuum dryer or the like, and then perform a drying treatment at about 50 ° C. to 200 ° C. for about 1 to 48 hours.

The Pd catalyst particles supported on the base material particles function as the main catalytically active sites in the three-way catalyst for exhaust gas purification of the present embodiment. As described above, the Pd catalyst particles can be transformed into a PdO / Nd ₂ O ₃ composite oxide, a solid solution, PdO, or a metal Pd depending on the external environment. Therefore, the oxidation state of the Pd catalyst particles is not particularly limited, but it is preferably PdO or metal Pd particles in a reducing atmosphere.

The content of the Pd catalyst particles supported on the base metal particles can be appropriately determined according to the desired performance, and is not particularly limited, but improves the catalyst performance over the entire range of lean environment, stoichiometric environment, and rich environment, and also has low temperature activity. From the viewpoint of improving the above, the amount converted into metal-palladium with respect to the total amount of the three-way catalyst for exhaust gas purification is preferably 0.1 to 10% by mass, more preferably 0.2 to 8% by mass, and further preferably 0. .3 to 6% by mass.

The Pd catalytic particles supported on the base metal particles preferably have an average crystallite diameter of 1 to 90 nm, more preferably 3 to 90 nm, from the viewpoint of maintaining a large number of catalytically active sites and obtaining high catalytic performance. It is 80 nm. The crystallite is the largest group that can be generally regarded as a single crystal, and the size of the crystallite is called the crystallite diameter. Further, in the present specification, the average crystallite diameter means a value calculated from Scherrer's equation represented by the following equation (1) based on the measurement result of the diffraction pattern measured by using an X-ray diffractometer. To do.
Crystallite diameter D (Å) = K · λ / (β · cosθ) ・ ・ ・ (1)
In equation (1), K is a Scherrer constant, where K = 0.9. Further, λ is the wavelength of the X-ray tube used, β is the half width, and θ is the diffraction angle (rad).

The three-way catalyst for exhaust gas purification of the present embodiment may contain a noble metal element (PM) and a platinum group element (PGM) other than Pd, but in consideration of use under high temperature conditions, other than Pd. It is preferable that the noble metal element (PM) and the platinum group element (PGM) of the above are substantially not contained. Here, "substantially free" means that the total amount of noble metal elements (PM) and platinum group elements (PGM) other than Pd is 0 to 1.0% by mass with respect to the total amount of the three-way catalyst for exhaust gas purification. It means that it is within the range, more preferably 0 to 0.5% by mass, and further preferably 0 to 0.3% by mass.

The shape of the three-way catalyst for exhaust gas purification of the present embodiment is not particularly limited. For example, the catalyst powder, which is an aggregate of composite particles in which Pd catalyst particles are supported on the base material particles, can be used as it is. Further, for example, the catalyst powder can be molded into an arbitrary shape to obtain a granular or pellet-shaped molding catalyst. Further, the three-way catalyst for purifying exhaust gas can be supported on a catalyst carrier. As the catalyst carrier used here, those known in the art can be appropriately selected. Typical examples thereof include ceramic monolith carriers made of cordierite, silicon carbide, silicon nitride and the like, metal honeycomb carriers made of stainless steel and the like, wire mesh carriers made of stainless steel and the like, but are not particularly limited thereto. It should be noted that these can be used alone or in combination of two or more.

Further, the three-way catalyst for exhaust gas purification of the present embodiment has a metal surface area (MSA: Metal Surface Area) per gram of palladium calculated by a carbon monoxide gas pulse adsorption method, that is, palladium, from the viewpoint of obtaining high catalytic performance. preferably the surface area is 15~30 (m ² / Pd_g), more preferably 16~30 (m ² / Pd_g), more preferably from 17~30 (m ² / Pd_g). Here, in the present specification, the palladium surface area of the exhaust gas purification three-way catalyst is measured, for example, by using a sample obtained by subjecting the exhaust gas purification three-way catalyst to be measured to an aging treatment (high temperature durability treatment). Examples described later from the CO adsorption amount (cc / g) per catalyst unit mass measured using a gas adsorption measuring device such as an apparatus (trade name: BEL-METAL-3, Microbell Truck Co., Ltd.) It means the value obtained by the conversion formula described in. This aging treatment is performed for the purpose of stabilizing the running performance of the three-way catalyst. In this aging treatment, heat treatment is performed at 1050 ° C. for 12 hours in an air atmosphere having a water concentration of 10%, and then reduction treatment is performed at 400 ° C. for 0.5 hours in a hydrogen gas atmosphere.

Further, the three-way catalyst for exhaust gas purification of the present embodiment preferably has a BET specific surface area of 10 to 50 m ² / g by the BET one-point method, more preferably 12 to 50 m ² / g, from the viewpoint of obtaining high catalytic performance. was 50 m ² / g, more preferably from 15 to 50 m ² / g. Here, in the present specification, the BET specific surface area of the exhaust gas purification three-way catalyst is a value measured by using a sample obtained by subjecting the exhaust gas purification three-way catalyst to be measured to the above-mentioned aging treatment (high temperature durability treatment). And.

The exhaust gas purification three-way catalyst described above is useful, for example, as an exhaust gas purification catalyst for an internal combustion engine, particularly as an exhaust gas purification catalyst for a gasoline vehicle.

As described above, the method for producing the three-way catalyst for exhaust gas purification is not particularly limited as long as a structure in which Pd catalyst particles are supported on the base material particles of the Nd solid-dissolved zirconia-based composite oxide can be obtained. From the viewpoint of producing a three-way catalyst for exhaust gas purification with good reproducibility, simple and low cost, the evaporation dry solid method (impregnation method) or the like is preferable.

As the evaporation-drying method, a production method in which the above-mentioned base metal particles are impregnated with an aqueous solution containing at least Pd ions and then heat-treated or chemically treated is preferable. By this impregnation treatment, Pd ions are adsorbed (adhered) to the surface of the base material particles in a highly dispersed state. The Pd ion can be added to the aqueous solution as various salts of palladium. The types of various salts used here are not particularly limited. In general, hydrochloride, oxy hydrochloride, nitrate, oxynitrate, carbonate, phosphate, acetate, oxalate, citrate and the like are preferable. Further, the content ratio of Pd ions in the aqueous solution can be appropriately adjusted so that the Pd catalyst particles have a desired content ratio in the obtained three-way catalyst for exhaust gas purification, and is not particularly limited. Needless to say, the aqueous solution used here may contain the above-mentioned optional components such as rare earth elements such as itum, scandium, lanthanum and praseodymium, transition metal elements, and unavoidable impurities.

The conditions of the heat treatment and the chemical treatment may be according to a conventional method and are not particularly limited. For example, the atmosphere at the time of heat treatment may be an oxidizing atmosphere, an atmospheric atmosphere, or a reducing atmosphere. The heat treatment temperature and its time vary depending on the composition of the desired Nd solid solution zirconia-based composite oxide and its stoichiometric ratio, but from the viewpoint of the formation and productivity of Pd catalyst particles, it is generally 500. It is preferably 0.1 to 12 hours at ~ 1100 ° C., more preferably 0.5 to 6 hours at 550 ° C. to 800 ° C. Prior to the heat treatment, vacuum drying may be performed using a vacuum dryer or the like, and the drying treatment may be performed at about 50 ° C. to 200 ° C. for about 1 to 48 hours. Further, as the chemical treatment, after the impregnation treatment in the evaporation-drying method, Pd ions may be hydrolyzed on the surface of the carrier using a basic component. As the basic component used here, amines such as ammonia and ethanolamine, alkali metal hydroxides such as caustic soda and strontium hydroxide, and alkaline earth metal hydroxides such as barium hydroxide are preferable. By these heat treatments and chemical treatments, Pd catalyst particles highly dispersed in nano-order size are generated on the surface of the base material particles.

When producing the molding catalyst, various known dispersion devices, kneading devices, and molding devices can be used. Further, when the catalyst carrier holds the three-way catalyst for purifying exhaust gas, various known coating methods, wash coating methods, and zone coating methods can be applied.

The three-way catalyst for exhaust gas purification of the present embodiment can be used by blending it with the catalyst layer of the catalyst converter for exhaust gas purification. For example, it can be carried out by providing a catalyst layer containing the three-way catalyst for exhaust gas purification of the present embodiment on a catalyst carrier such as the ceramic monolith carrier described above. Further, the catalyst area of the exhaust gas purification catalyst converter is known in the art as one or more catalyst layers, regardless of whether the catalyst area is a single layer having only one catalyst layer or a laminate composed of two or more catalyst layers. It may be any of the laminated bodies in combination with one or more other layers of. For example, in the case where the exhaust gas purification catalyst converter has at least an oxygen storage layer and a catalyst layer on the catalyst carrier, the catalyst layer contains at least the three-way catalyst for exhaust gas purification to be heat resistant. It can be a catalytic converter for exhaust gas purification having excellent properties and three-way purification performance. Considering the trend of tightening exhaust gas regulations, the layer structure is preferably two or more layers.

The method for forming the catalyst layer may be carried out according to a conventional method, and is not particularly limited. As an example, the three-way catalyst for exhaust gas purification of the present embodiment, an aqueous medium, a binder known in the art, other catalysts, cocatalyst particles, OSC material, base material particles, additives, etc., if necessary, etc. And are mixed at a desired blending ratio to prepare a slurry-like mixture, and the obtained slurry-like mixture is applied to the surface of the catalyst carrier, and can be dried and calcined. At this time, if necessary, an acid or a base can be blended for pH adjustment, or a surfactant, a dispersion resin, or the like for adjusting the viscosity or improving the slurry dispersibility can be blended. As a method for mixing the slurry, pulverization and mixing using a ball mill or the like can be applied, but other pulverization or mixing methods can also be applied.

The method for applying the slurry-like mixture to the catalyst carrier may be carried out according to a conventional method, and is not particularly limited. Various known coating methods, wash coating methods, and zone coating methods can be applied. Then, after the slurry-like mixture is added, the exhaust gas purification catalyst converter including the catalyst layer containing the three-way catalyst for exhaust gas purification of the present embodiment can be obtained by drying or firing according to a conventional method. ..

The exhaust gas purification catalytic converter described above can be arranged in the exhaust system of various engines. The number and location of exhaust gas purification catalytic converters can be appropriately designed according to the exhaust gas regulations. For example, when exhaust gas regulations are strict, the number of installation locations may be two or more, and the installation locations may be located under the floor behind the catalyst directly under the exhaust system. Further, according to the catalyst composition containing the three-way catalyst for exhaust gas purification and the catalyst converter for exhaust gas purification of the present embodiment, in various running specifications including not only at the time of starting at a low temperature but also at the time of high-speed running at a high temperature. , CO, HC, NOx can exert an excellent effect on the purification reaction.

The features of the present invention will be described in more detail below with reference to Test Examples, Examples and Comparative Examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention.

[Measurement of palladium surface area]
For the palladium surface area (m ² / Pd_g), first, the CO adsorption amount M (cc / g) of each performance evaluation sample sample is measured by the carbon monoxide gas pulse adsorption method, and the Pd surface area per CO adsorption amount in the simple ideal model. Using (3517.487 m ² / mmol) as the coefficient W, it is calculated from the CO adsorption amount M and the coefficient W, and the volume of the ideal gas in the standard state (22.4 L / mol) based on the following formula (2). did.
Palladium surface area (m ^{2 /} g_Pd) = W * M / 22.4 ... (2)
The coefficient W used at this time is the same as that of the alumina particles carrying 1% by mass of Pd (palladium average crystallite diameter: 45.4 nm, density: 12.023 g / cc, surface area of 10.99215 m ² / g). It was calculated based on the CO adsorption amount (0.07 cc / g) in the carbon monoxide gas pulse adsorption method.
In addition, in the measurement of the CO adsorption amount M by the carbon monoxide gas pulse adsorption method, a metal dispersibility measuring device (trade name: BEL-METAL-3, manufactured by Microbell Truck Co., Ltd.) is used, and the temperature is 400 ° C. under a hydrogen atmosphere. After reduction, purge with helium gas, and under the condition of cooling to 25 ° C., 10% CO gas pulse is injected every minute until CO adsorption disappears, and the CO adsorption amount of the sample for performance evaluation is calculated. did. In the measurement of the palladium surface area of the three-way catalyst for exhaust gas purification, 1.0 g of a sample subjected to heat treatment at 1050 ° C. for 12 hours in an air atmosphere having a water concentration of 10% was used.

[Measurement of BET specific surface area]
For the BET specific surface area, use a specific surface area / pore distribution measuring device (trade name: BELSORP-mini II, manufactured by Microtrac Bell Co., Ltd.) and analysis software (trade name: BEL_Master, manufactured by Microtrac Bell Co., Ltd.). , BET one-point method. In the measurement of the BET specific surface area of the three-way catalyst for exhaust gas purification, 0.1 g of a sample subjected to heat treatment at 1050 ° C. for 12 hours in an air atmosphere having a water concentration of 10% was used.

(Example 1)
As the base material particles, Nd solid-dissolved zirconia-based composite oxide (Nd ₂ O ₃ : 26% by mass, ZrO ₂ : 74% by mass: D ₅₀ = 3.1 μm, BET specific surface area: 46 m ² / g) was used. Next, a palladium (II) nitrate solution (containing 20% by mass in terms of PdO) is prepared, the Nd solid-soluble zirconia-based composite oxide is impregnated with the palladium (II) nitrate solution, and calcined at 600 ° C. for 30 minutes. The powder catalyst of Example 1 (three-way catalyst for exhaust gas purification, supported amount in terms of Pd: 1.0% by mass) was obtained.
Then, the obtained powder catalyst was allowed to stand in a furnace, heat-treated at 1050 ° C. for 12 hours in an air atmosphere having a water concentration of 10%, and then reduced for 0.5 hours at 400 ° C. in a hydrogen gas atmosphere. By doing so, a sample for performance evaluation (three-way catalyst for exhaust gas purification) of Example 1 was obtained.
When a three-way catalyst powder sample for exhaust gas purification was observed using a scanning transmission electron microscope (STEM) at a magnification of 1 million times, fine Pd catalyst particles were observed on a base material particle having an average particle diameter D ₅₀ of 1 to 100 μm. Was confirmed to be supported.

(Example 2)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the Nd solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 35% by mass, ZrO ₂ : 65% by mass: D ₅₀ = 3.9 μm, The same operation as in Example 1 was performed except that the BET specific surface area (60 m ² / g) was used, and the powder catalyst of Example 2 (three-way catalyst for exhaust gas purification, supported amount in terms of Pd: 1.0 mass%) was performed. ) And a sample for performance evaluation were obtained.

(Example 3)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the Nd solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 43% by mass, ZrO ₂ : 57% by mass: D ₅₀ = 2.0 μm, The same operation as in Example 1 was performed except that the BET specific surface area: 57 m ² / g) was used, and the powder catalyst of Example 3 (three-way catalyst for exhaust gas purification, Pd-equivalent carrier amount: 1.0% by mass). ) And a sample for performance evaluation were obtained.

(Example 4)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the Nd solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 50% by mass, ZrO ₂ : 50% by mass: D ₅₀ = 2.0 μm, The same operation as in Example 1 was performed except that the BET specific surface area (BET specific surface area: 53 m ² / g) was used, and the powder catalyst of Example 4 (three-way catalyst for exhaust gas purification, supported amount in terms of Pd: 1.0% by mass). ) And a sample for performance evaluation were obtained.

(Example 5)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the NdLa solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 26% by mass, La ₂ O ₃ : 8% by mass, ZrO ₂ : 66% by mass) %: D ₅₀ = 2.0 μm, BET specific surface area: 59 m ² / g), the same operation as in Example 1 was performed, and the powder catalyst of Example 5 (three-way catalyst for exhaust gas purification, Pd conversion) was performed. Amount carried: 1.0% by mass) and a sample for performance evaluation were obtained.

(Example 6)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the NdLa solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 26% by mass, La ₂ O ₃ : 15% by mass, ZrO ₂ : 59% by mass) The same operation as in Example 1 was performed except that%: D ₅₀ = 2.5 μm, BET specific surface area: 65 m ² / g), and the powder catalyst of Example 6 (three-way catalyst for exhaust gas purification, Pd conversion) was performed. Amount carried: 1.0% by mass) and a sample for performance evaluation were obtained.

(Example 7)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the NdLa solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 35% by mass, La ₂ O ₃ : 15% by mass, ZrO ₂ : 50% by mass) The same operation as in Example 1 was performed except that%: D ₅₀ = 2.1 μm, BET specific surface area: 51 m ² / g), and the powder catalyst of Example 7 (three-way catalyst for exhaust gas purification, Pd conversion) was performed. Amount carried: 1.0% by mass) and a sample for performance evaluation were obtained.

(Example 8)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the NdLa solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 43% by mass, La ₂ O ₃ : 3% by mass, ZrO ₂ : 54% by mass) %: D ₅₀ = 1.9 μm, BET specific surface area: 62 m ² / g) The same operation as in Example 1 was carried out, except that the powder catalyst of Example 8 (three-way catalyst for exhaust gas purification, Pd conversion) was used. Amount carried: 1.0% by mass) and a sample for performance evaluation were obtained.

(Comparative Example 1)
Except for using a zirconia-based oxide (ZrO ₂ : 100% by mass: D ₅₀ = 0.1 μm, BET specific surface area: 25 m ² / g) instead of the Nd solid-dissolved zirconia-based composite oxide used in Example 1. Performed the same operation as in Example 1 to obtain a powder catalyst of Comparative Example 1 (three-way catalyst for exhaust gas purification, supported amount in terms of Pd: 1.0% by mass) and a sample for performance evaluation.

(Comparative Example 2)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the Nd solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 9% by mass, ZrO ₂ : 91% by mass: D ₅₀ = 2.5 μm, The same operation as in Example 1 was performed except that the BET specific surface area: 65 m ² / g) was used, and the powder catalyst of Comparative Example 2 (three-way catalyst for exhaust gas purification, supported amount in terms of Pd: 1.0 mass%). ) And a sample for performance evaluation were obtained.

(Comparative Example 3)
Instead of the Nd solid-dissolved zirconia-based composite oxide used in Example 1, the Nd solid-dissolved zirconia-based composite oxide (Nd ₂ O ₃ 18% by mass, ZrO ₂ : 82% by mass: D ₅₀ = 2.8 μm, BET The same operation as in Example 1 was performed except that the specific surface area (specific surface area: 64 m ² / g) was used, and the ternary catalyst for exhaust gas purification (supported amount in terms of Pd: 1.0 mass%) and performance evaluation of Comparative Example 3 were performed. Samples were obtained.

(Comparative Example 4)
Instead of the Nd solid-soluble zirconia-based composite oxide used in Example 1, the Nd solid-soluble zirconia-based composite oxide (Nd ₂ O ₃ : 75% by mass, ZrO ₂ : 25% by mass: D ₅₀ = 2.5 μm, The same operation as in Example 1 was carried out except that the BET specific surface area (25 m ² / g) was used, and the ternary catalyst for exhaust gas purification (supported amount in terms of Pd: 1.0 mass%) and performance of Comparative Example 4 were performed. An evaluation sample was obtained.

The palladium surface area and the BET specific surface area were measured for the performance evaluation samples of Examples 1 to 8 and Comparative Examples 1 to 4, respectively. Table 1 shows the measurement results. Further, a STEM photograph of the three-way catalyst for exhaust gas purification (sample for performance evaluation) of Example 7 is shown in FIG.

As is clear from Table 1, it was confirmed that the exhaust gas purification three-way catalyst of Examples 1 to 8 corresponding to the present invention has a larger palladium surface area than the exhaust gas purification three-way catalyst of Comparative Examples 1 to 4. It was. It was also shown that the BET specific surface area tends to decrease as the solid solution amount of the rare earth element increases. On the other hand, no clear correlation between the palladium surface area and the BET specific surface area could be confirmed. From this, it is shown that the number of catalytically active sites of the three-way catalyst for exhaust gas purification is not necessarily proportional to the BET specific surface area, and even if the BET specific surface area is relatively small, the palladium surface area is large and the catalytic performance is large. It was confirmed that a three-way catalyst for purifying exhaust gas can be realized.

[Lab measurement of HC and NO purification performance]
Next, the HC and NO purification performances of the above performance evaluation samples were evaluated, respectively. Here, a sample for performance evaluation that has been heat-treated at 800 ° C. for 20 hours in an air atmosphere in a furnace is placed in a sample holder by weighing 50 mg each, and is placed in a TPD reactor (heated desorption gas analyzer, trade name: BEL). A purification performance test was conducted at 300 ° C. in a steady air flow of the model gas using Mass, manufactured by Microtrac Bell Co., Ltd.

The model gas composition used here is shown in Table 2.

The HC purification rate and the NO purification rate were calculated based on the following equations (2) and (3).
HC purification rate (%) = 100- (HC-MASS peak intensity (at the time of measurement) / HC-MASS peak intensity (Blank)) x 100 ... (2)
NO purification rate (%) = 100- (NO-MASS peak intensity (at the time of measurement) / NO-MASS peak intensity (Blank)) x 100 ... (3)

The measurement results of HC and NO purification performance are shown in Table 3.

As is clear from Table 3, the exhaust gas purification three-way catalyst of the examples corresponding to the present invention has achieved both the HC purification rate and the NO purification rate of 50% or more, and the exhaust gas purification three-way catalyst of the comparative example. It was confirmed that the catalyst performance was superior to that of the catalyst.

The three-way catalyst for exhaust gas purification and the catalyst converter for exhaust gas purification of the present invention can be widely and effectively used as a three-way catalyst for reducing NOx, CO, HC, etc. in exhaust gas, and have higher heat resistance than a diesel engine. It can be used particularly effectively in gasoline engine applications where Further, the three-way catalyst for exhaust gas purification of the present invention can be effectively used as a TWC for a catalyst converter directly under an engine, a catalyst converter directly under a tandem arrangement, or the like.

Claims (8)

Nd and Zr as constituent metal elements, the following mass ratio in terms of oxide:
ZrO ₂ 50 to 59 wt%;
Nd ₂ O ₃ 35 ~50 wt%;
Nd solid solution zirconia-based composite oxide base material particles contained in
Pd catalyst particles supported on the base material particles and
At least it contains,
The palladium surface area calculated by the carbon monoxide gas pulse adsorption method is 15 to 30 (m ² / Pd _ g) .
Three-way catalyst for exhaust gas purification. The three-way catalyst for exhaust gas purification according to claim 1, wherein the Pd catalyst particles are contained in an amount of 0.1 to 10% by mass in terms of metallic palladium. The Nd solid-soluble zirconia-based composite oxide contains at least one or more rare earth elements selected from the group consisting of yttrium, scandium, lanthanum, and praseodymium as constituent metal elements in a total of 0 to 20% by mass in terms of oxide. Item 3. The ternary catalyst for purifying exhaust gas according to Item 1 or 2. The Nd solid solution zirconia-based composite oxide contains La as a constituent metal element and has the following mass ratio in terms of oxide:
La ₂ O ₃ 0 to 18 wt%;
The three-way catalyst for exhaust gas purification according to any one of claims 1 to 3 including the above. The three-way catalyst for exhaust gas purification according to any one of claims 1 to 4, wherein the base material particles have an average particle diameter D ₅₀ of 1 to 100 μm. The BET specific surface area is 10 to 50 (m ² / g).
The three-way catalyst for exhaust gas purification according to any one of claims 1 to 5 . Nd and Zr as constituent metal elements, the following mass ratio in terms of oxide:
ZrO ₂ 50 to 59 wt%;
Nd ₂ O ₃ 35 ~50 wt%;
Step of preparing base particle of Nd solid solution zirconia-based composite oxide contained in
A step of applying an aqueous solution containing at least Pd ions to the surface of the base material particles, and a step of heat-treating or chemically treating the base material particles after treatment to support the Pd catalyst particles on the surface of the base material particles. , Characterized by having at least
A method for producing a three-way catalyst for exhaust gas purification , which has a palladium surface area of 15 to 30 (m ² / Pd_g) calculated by a carbon monoxide gas pulse adsorption method. At least a catalyst carrier, an oxygen storage layer provided on the catalyst carrier, and a catalyst layer provided on the oxygen storage layer are provided.
The catalyst layer contains the three-way catalyst for exhaust gas purification according to any one of claims 1 to 6 .
Catalytic converter for exhaust gas purification.