JP2018075550A - Three-dimensional catalyst for exhaust gas purification and manufacturing method therefor, and catalyst converter for exhaust gas solidification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional catalyst for exhaust gas purification large in palladium surface area, excellent in heat resistance and three-dimensional purification performance, easy to be manufactured and excellent in productivity and a manufacturing method therefor, and a catalyst converter for exhaust gas purification.SOLUTION: There is provided a three-dimensional catalyst for exhaust gas purification, under a reducing atmosphere, containing at least a base material particle of Nd dissolved zirconia-based composite oxide containing Nd and Zr of following mass percentages in terms of oxide as constitutional metal elements, and a Pd catalyst particle carried on the base material particle. The three-dimensional catalyst for exhaust gas purification preferably has palladium surface area calculated by a carbon monoxide gas pulse adsorption method of 15 to 30 (m/Pd_g). ZrO50 to 75 mas%; NdO25 to 50 mass%.SELECTED DRAWING: Figure 1

Description

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

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

  In this type of exhaust gas purifying catalyst, in order to reduce the amount of relatively expensive PGM used and to ensure high catalytic activity, the catalyst metal is supported on the carrier in the form of fine particles. However, when the catalyst metal particles on the support are exposed to a high temperature environment, the particles grow by particle sintering, thereby causing a problem that the catalytically active sites are remarkably reduced.

As a technique for suppressing the sintering of the catalyst metal, for example, Patent Document 1 discloses a carrier in which a mixture in which primary particles of Al ₂ O ₃ particles and predetermined metal oxide particles are mixed in nano order is used. An exhaust gas purifying catalyst having a platinum group element supported on a carrier is disclosed. According to this technique, since the primary particles of Al ₂ O _{3 and} the primary particles of the 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, the decrease in the surface area and 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 purifying oxidation catalyst having a support composed of AZT oxide or AZ oxide and a noble metal that catalyzes the oxidation of carbon monoxide supported on the support. . According to this technique, an atom of a noble metal such as palladium or platinum is formed via an oxygen atom at a base point on the surface of a support made of AZT oxide or an AZ oxide, that is, a site of an atom or atomic group exhibiting basic properties. Since (ion) is firmly fixed (supported), it is said that the sintering suppressing effect is high and the grain growth of the noble metal can be suppressed.

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

On the other hand, as a three-way catalyst with improved heat resistance, Patent Document 3 discloses 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 so as to satisfy the charge neutrality condition) Exhaust gas purification three-way catalyst comprising a solid solution component Is disclosed.

  On the other hand, Patent Documents 4 and 5 disclose ceria doped with rare earth elements such as yttrium, lanthanum, neodymium, praseodymium and gadolinium as a promoter (oxygen storage material) having an oxygen storage capacity (OSC). Zirconia-based metal oxides are disclosed.

International Publication No. 2012/121085 Pamphlet International Publication No. 2012/137930 Pamphlet JP 2013-166130 A International Publication No. 2011/083157 Pamphlet International Publication No. 2010/097307 Pamphlet

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

  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, and a catalytic converter for exhaust gas purification, which have a large palladium surface area, excellent heat resistance and three-way purification performance, easy to manufacture and excellent in productivity. It is to provide.

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

That is, the present invention provides various specific modes shown below.
(1) Nd and Zr as constituent metal elements in the following mass proportions in terms of oxide: ZrO ₂ 50 to 75% by mass; Nd ₂ O ₃ 25 to 50% by mass; A three-way catalyst for exhaust gas purification, comprising at least base material particles and Pd catalyst particles supported on the base material particles.
(2) The exhaust gas purification three-way catalyst 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 solution zirconia-based composite oxide comprises at least one or more rare earth elements selected from the group consisting of yttrium, scandium, lanthanum, and praseodymium as constituent metal elements in total 0 to 20 mass in terms of oxide. The three-way catalyst for exhaust gas purification as described in (1) or (2).
(4) The Nd solid solution zirconia composite oxide contains La as a constituent metal element in the following mass ratio in terms of oxide: La ₂ O _{3 0 to} 18% by mass; (1) to (3) The three-way catalyst for exhaust gas purification according to any one of the above.
(5) The exhaust gas purification three-way catalyst according to any one of (1) to (4), wherein the base material particles have an average particle diameter D ₅₀ of 1 to 100 μm.
(6) The exhaust gas purification three-way catalyst according to any one of (1) to (5), wherein a palladium surface area calculated by a 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), wherein the BET specific surface area is 10 to 50 m ² / g.

(8) Nd and Zr as constituent metal elements in the following mass proportions in terms of oxide: ZrO ₂ 50 to 75% by mass; Nd ₂ O ₃ 25 to 50% by mass; A step of preparing 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 base material particles after the treatment, A method for producing a three-way catalyst for exhaust gas purification, comprising at least a step of supporting Pd catalyst particles on the catalyst.
(9) At least a catalyst carrier, an oxygen storage layer provided on the catalyst carrier, and a catalyst layer provided on the oxygen storage layer, wherein the catalyst layer is any one of (1) to (7) An exhaust gas purifying catalytic converter comprising the three-way catalyst for purifying exhaust gas according to claim 1.

  According to the present invention, a three-way catalyst for exhaust gas purification, a manufacturing method thereof, a catalyst converter for exhaust gas purification, etc., which have a large palladium surface area, excellent heat resistance and three-way purification performance, easy to manufacture and excellent in productivity, are realized. can do. The exhaust gas purifying catalyst of the present invention is a catalyst particle having a composite structure in which a large number of minute active sites (Pd catalyst particles) are supported on a base material particle of an Nd solid solution zirconia composite oxide, and its composition and structure Based on the above, it can be particularly suitably used as a three-way catalyst (TWC: Tree Way Catalyst) for reducing NOx, CO, HC and the like in exhaust gas. The exhaust gas purifying catalyst of the present invention can be mounted on an engine direct catalytic converter, a tandem direct catalytic converter, or the like, thereby reducing canning costs.

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

  Hereinafter, embodiments of the present invention will be described in detail. In addition, the following embodiment is an illustration for demonstrating this invention, and this invention is not limited to these. In this specification, for example, the description of a numerical range of “1 to 100” includes both the upper limit value “1” and the lower limit value “100”. This also applies to other numerical range notations.

The exhaust gas purifying three-way catalyst of the present embodiment contains at least Nd solid solution zirconia composite oxide base material particles having a specific composition and Pd catalyst particles supported on the base material particles. This Nd solid solution zirconia-based composite oxide contains at least neodymium (Nd), zirconium (Zr), and oxygen (O) as constituent elements, and Nd and Zr are converted into the following mass in terms of oxide. It is contained in proportion.
ZrO ₂ : 50 to 75% by mass
Nd ₂ O _3: 25~50 wt%

  Realizing a three-way catalyst for exhaust gas purification in which fine Pd catalyst particles are supported in a highly dispersed manner on the base material particles by using the base material particles of the Nd solid solution zirconia composite oxide having such a composition. Can do. Hereinafter, the presumed action in the three-way catalyst for exhaust gas purification of this embodiment will be described.

As described above, in this type of catalyst, when exposed to a high temperature environment, the catalyst particles on the base material particles grow together by sintering, thereby reducing the number of catalytically active sites. It is known that performance decreases. On the other hand, in the three-way catalyst for exhaust gas purification according to the present embodiment, when the external environment is switched from the reducing atmosphere to the oxidizing atmosphere, Nd and Pd catalyst particles contained in the base material particles are mixed oxide or 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 solid solution. That is, in this embodiment, the Pd catalyst particles are used as a so-called PdO / Nd ₂ O ₃ mixed oxide, and fine Pd catalyst particles are highly dispersed on the base material particles according 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 improved. As a result of these, it is presumed that a three-way catalyst for exhaust gas purification having excellent heat resistance and three-way purification performance has been realized. However, the action is not limited to these.

  In addition, since it is as above, the said base material particle | grains and Pd catalyst particle should just be confirmed in a reducing atmosphere, and the property of Pd catalyst particle | grains in an oxidizing atmosphere and stoichiometric atmosphere is not specifically limited. Here, in the present specification, the reducing atmosphere means a state of standing at 400 ° C. for 0.5 hours or more in a hydrogen gas atmosphere. The Pd catalyst particles can be confirmed using, for example, a scanning transmission electron microscope (STEM) having a magnification of 1,000,000 times, HD-2000 manufactured by Hitachi High-Technologies Corporation. Hereinafter, each component will be described in detail.

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

On the other hand, the mass ratio of Nd contained in the Nd solid solution of zirconia-based composite oxide, an oxide (Nd ₂ O ₃₎ in terms of, preferably 26 to 50 wt%, more preferably from 30 to 50 wt%, further Preferably it is 35-50 mass%. By using a zirconia composite oxide in which Nd, which is a rare earth element, is dissolved in this manner, 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 composite oxide may contain other elements in addition to the constituent elements described above. For example, unless the effects of the present invention are significantly impaired, rare earth elements such as yttrium, cerium, scandium, lanthanum, praseodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium are included. You may go out. These rare earth elements can be used individually by 1 type or in combination of 2 or more types as appropriate.

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

A preferred embodiment is a Nd—La solid solution zirconia-based composite oxide containing at least Nd, Zr, La and O as constituent elements, wherein Nd, Zr and La are represented by the following mass ratios in terms of oxides: It contains what is contained in.
ZrO ₂ : 50 to 75% by mass
Nd ₂ O _3: 25~50 wt%
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 rare earth elements described above, cerium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium are Nd solid solution. It is preferable that the zirconia composite oxide is not substantially contained. Here, “substantially not containing” means that the mass ratio in terms of oxide is 0 to 5 mass% with respect to the Nd solid solution zirconia composite oxide, and more preferably 0 to 3%. It is mass%, More preferably, it is 0-1 mass%.

  In addition, the Nd solid solution zirconia-based composite oxide may contain hafnium (Hf), which is usually contained in the zirconia ore in an amount of about 1 to 2% by mass, as an inevitable impurity. Here, the total amount of inevitable impurities excluding hafnium is preferably 0.3% by mass or less. In the Nd solid solution zirconia composite oxide, a part of zirconium may be substituted with an alkali metal element, an alkaline earth metal element, or the like as long as the effects of the present invention are not significantly impaired. Furthermore, the Nd solid solution 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. You may contain.

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

  As the base particles, various grades of commercial products can be used. Moreover, the Nd solid solution zirconia composite oxide having the above-described composition can also be produced by a method known in the art. Although the manufacturing method of Nd solid solution zirconia type complex oxide is not specifically limited, A coprecipitation method and an alkoxide method are preferable.

  As the coprecipitation method, for example, an alkaline substance is added to an aqueous solution in which a zirconium salt, a neodymium salt, and a rare earth metal element to be blended as necessary are mixed in a predetermined stoichiometric ratio, and then hydrolyzed or a precursor is co-mixed. A production method is preferred in which the product is precipitated and the hydrolysis product or coprecipitate is baked. The kind of various salt used here is not specifically limited. In general, hydrochloride, oxyhydrochloride, nitrate, oxynitrate, carbonate, phosphate, acetate, oxalate, citrate and the like are preferable. Moreover, the kind of alkaline substance is not particularly limited. In general, an aqueous ammonia solution is preferred. As the alkoxide method, for example, a production method in which a mixture obtained by mixing zirconium alkoxide, neodymium alkoxide, and rare earth metal element to be blended as necessary at a predetermined stoichiometric ratio is hydrolyzed and then fired is preferable. The kind of alkoxide used here is not particularly limited. In general, methoxide, ethoxide, propoxide, isopropoxide, butoxide, and these ethylene oxide adducts are preferable. Further, the rare earth metal element may be blended as a metal alkoxide or as the various salts described above.

  The firing conditions may be in accordance with conventional methods and are not particularly limited. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and a neutral atmosphere. The firing temperature and the treatment time vary depending on the desired composition of the Nd solid solution zirconia composite oxide and its stoichiometric ratio. From the viewpoint of productivity and the like, the firing temperature and the treatment time are generally 1 to 150 ° C to 1300 ° C. -12 hours are preferable, and more preferably 350 ° C to 800 ° C for 2 to 4 hours. Prior to the high temperature firing, it is preferable to perform drying under reduced pressure using a vacuum dryer or the like, and to 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 main catalytic active sites in the three-way catalyst for exhaust gas purification of this embodiment. As described above, the Pd catalyst particles can be changed into a PdO / Nd ₂ O ₃ composite oxide, solid solution, PdO, or metal Pd according to the external environment. Therefore, the oxidation state of the Pd catalyst particles is not particularly limited, but is preferably PdO or metal Pd particles in a reducing atmosphere.

  The content of the Pd catalyst particles supported on the base material 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 standpoint of improving the amount, the metal palladium equivalent of the total amount of the exhaust gas purification three-way catalyst is preferably 0.1 to 10% by mass, more preferably 0.2 to 8% by mass, and still more preferably 0. 3 to 6% by mass.

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

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

  The shape of the exhaust gas purifying three-way catalyst 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 base material particles, can be used. Further, for example, the catalyst powder can be formed into an arbitrary shape to form a granular or pellet shaped catalyst. Further, the exhaust gas purifying three-way catalyst can be supported on a catalyst carrier. As the catalyst carrier used here, those known in the art can be appropriately selected. Representative examples include a ceramic monolith support made of cordierite, silicon carbide, silicon nitride, etc., a metal honeycomb support made of stainless steel, a wire mesh carrier made of stainless steel, etc., but is not particularly limited thereto. In addition, these can be used individually by 1 type or in combination of 2 or more types as appropriate.

Further, the exhaust gas purification three-way catalyst of the present embodiment has a metal surface area (MSA: Metal Surface Area) per 1 g of palladium calculated by a carbon monoxide gas pulse adsorption method from the viewpoint of obtaining high catalyst performance, that is, palladium. 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 by, for example, measuring the metal dispersion using a sample obtained by subjecting the exhaust gas purification three-way catalyst to aging treatment (high temperature durability treatment). From the CO adsorption amount (cc / g) per unit mass of the catalyst measured using a gas adsorption measuring device such as a device (trade name: BEL-METAL-3, Microbell Track Co., Ltd.), Examples described later 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 moisture concentration of 10%, and then reduction treatment is performed at 400 ° C. for 0.5 hours in a hydrogen gas atmosphere.

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

  The above-described three-way catalyst for exhaust gas purification 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 automobile.

  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 solution zirconia composite oxide is obtained. From the viewpoint of producing a three-way catalyst for exhaust gas purification with good reproducibility and at low cost, the evaporation to dry method (impregnation method) and the like are preferable.

  As the evaporation to dryness method, a production method in which the above-described base material particles are impregnated with an aqueous solution containing at least Pd ions and then heat treatment or chemical treatment is preferable. By this impregnation treatment, Pd ions are adsorbed (attached) to the surface of the base material particles in a highly dispersed state. In addition, Pd ion can be mix | blended with aqueous solution as various salts of palladium. The kind of various salt used here is not specifically limited. In general, hydrochloride, oxyhydrochloride, 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, for example, rare earth elements such as yttrium, scandium, lanthanum, and praseodymium, transition metal elements, and inevitable impurities.

  The conditions for the heat treatment and the chemical treatment are not particularly limited as long as they follow a conventional method. For example, the atmosphere during the heat treatment may be any of an oxidizing atmosphere, an air atmosphere, and a reducing atmosphere. The heat treatment temperature and the time vary depending on the desired composition of the Nd solid solution zirconia-based composite oxide and its stoichiometric ratio, but from the viewpoint of the production and productivity of Pd catalyst particles, 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 a drying process may be performed at about 50 ° C. to 200 ° C. for about 1 to 48 hours. As the chemical treatment, Pd ions may be hydrolyzed on the surface of the carrier using a basic component after the impregnation treatment in the evaporation to dryness method. The basic component used here is preferably an amine such as ammonia or ethanolamine, an alkali metal hydroxide such as caustic soda or strontium hydroxide, or an alkaline earth metal hydroxide such as barium hydroxide. By these heat treatment and chemical treatment, Pd catalyst particles highly dispersed in a nano-order size are generated on the surface of the base material particles.

  It should be noted that various known dispersing devices, kneading devices, and molding devices can be used when producing the molded catalyst. In addition, when the exhaust gas purification three-way catalyst is held on the catalyst carrier, various known coating methods, wash coat methods, and zone coat methods can be applied.

  The three-way catalyst for exhaust gas purification of the present embodiment can be used by being blended in the catalyst layer of the catalytic converter for exhaust gas purification. For example, it can be implemented by providing a catalyst layer containing the exhaust gas purification three-way catalyst of the present embodiment on a catalyst carrier such as the ceramic monolith carrier described above. Further, the catalyst area of the exhaust gas purifying catalytic converter may be a single layer having only one catalyst layer or a laminate composed of two or more catalyst layers, and is known in the art as one or more catalyst layers. Any of the laminates combined with one or more other layers may be used. For example, when the exhaust gas purification catalytic converter has a multilayer structure having at least an oxygen storage layer and a catalyst layer on the catalyst carrier, at least the catalyst layer contains the three-way catalyst for exhaust gas purification according to the present embodiment. The exhaust gas purifying catalytic converter can be made excellent in performance and ternary purification performance. Considering the trend of stricter exhaust gas regulations, the layer structure is preferably two or more layers.

  The method for forming the catalyst layer may be performed according to a conventional method, and is not particularly limited. For example, a three-way catalyst for exhaust gas purification according to the present embodiment, an aqueous medium, and a binder, other catalyst, promoter particles, OSC material, base material particles, additives, and the like known in the art as necessary. 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, followed by drying and firing. At this time, if necessary, an acid or a base may be blended for adjusting the pH, or a surfactant or a dispersing resin for adjusting the viscosity or improving the slurry dispersibility may be blended. In addition, as a mixing method of the slurry, pulverization and mixing by 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 performed according to a conventional method, and is not particularly limited. Various known coating methods, wash coating methods, and zone coating methods can be applied. And after provision of a slurry-like mixture, the exhaust gas purification catalytic converter provided with the catalyst layer containing the exhaust gas purification three-way catalyst of this embodiment can be obtained by performing drying and firing according to a conventional method. .

  The above-described exhaust gas purifying catalytic converter can be disposed in the exhaust system of various engines. The number and location of the exhaust gas purifying catalytic converter can be appropriately designed in accordance with exhaust gas regulations. For example, when exhaust gas regulations are strict, the number of installation locations can be two or more, and the installation location can be arranged at the lower floor position behind the catalyst directly under the exhaust system. And, according to the catalyst composition containing the three-way catalyst for exhaust gas purification and the catalytic converter for exhaust gas purification of the present embodiment, in various travel specifications including not only at the start at low temperature but also at high speed at high temperature. , CO, HC and NOx can exhibit excellent effects in the purification reaction.

  Hereinafter, the features of the present invention will be described more specifically with reference to test examples, examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

[Measurement of palladium surface area]
For the palladium surface area (m ² / Pd_g), the CO adsorption amount M (cc / g) of each sample for performance evaluation was first measured by the carbon monoxide gas pulse adsorption method, and the Pd surface area per CO adsorption amount in the simple ideal model was measured. (3517.487 m ² / mmol) is used as the coefficient W, and is calculated based on the following formula (2) from the CO adsorption amount M and the coefficient W and the volume (22.4 L / mol) of the ideal gas in the standard state. did.
Palladium surface area (m ² /g_Pd)=W*M/22.4 (2)
The coefficient W used at this time is that of alumina particles (palladium average crystallite diameter: 45.4 nm, density: 12.033 g / cc, surface area 10.99215 m ² / g) supporting 1% by mass of Pd. Calculation was 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 dispersion degree measuring device (trade name: BEL-METAL-3, Microbell Track Co., Ltd.) is used and a hydrogen atmosphere at 400 ° C. After reduction, purify with helium gas and cool to 25 ° C. Inject 10% CO gas pulse every minute until no CO adsorption is observed, and calculate the CO adsorption amount of the sample sample for performance evaluation. did. In the measurement of the palladium surface area of the exhaust gas purification three-way catalyst, 1.0 g of a sample subjected to heat treatment at 1050 ° C. for 12 hours in an air atmosphere having a moisture concentration of 10% was used.

[Measurement of BET specific surface area]
The BET specific surface area uses a specific surface area / pore distribution measuring device (trade name: BELSORP-mini II, manufactured by Microtrack Bell) and analysis software (trade name: BEL_Master, manufactured by Microtrack Bell). The BET one-point method was used. 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 a heat treatment for 12 hours at 1050 ° C. in an air atmosphere having a moisture concentration of 10% was used.

Example 1
Nd solid solution zirconia 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 as the base material particles. Next, a palladium (II) nitrate solution (containing 20% by mass in terms of PdO) is prepared, and the Nd solid solution zirconia-based composite oxide is impregnated with the palladium (II) nitrate solution and baked at 600 ° C. for 30 minutes. Thus, 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.
Thereafter, the obtained powder catalyst is left still in a furnace, and after heat treatment at 1050 ° C. for 12 hours in an air atmosphere having a moisture concentration of 10%, reduction treatment is performed at 400 ° C. for 0.5 hours in a hydrogen gas atmosphere. By performing, the sample for performance evaluation of Example 1 (three-way catalyst for exhaust gas purification) was obtained.
When a three-way catalyst powder sample for exhaust gas purification was observed with a scanning transmission electron microscope (STEM) at a magnification of 1,000,000, fine Pd catalyst particles were formed on the base material particles having an average particle diameter D ₅₀ of 1 to 100 μm. Was confirmed to be supported.

(Example 2)
Instead of the Nd solid solution zirconia composite oxide used in Example 1, Nd solid solution zirconia composite oxide (Nd ₂ O ₃ : 35% by mass, ZrO ₂ : 65% by mass: D ₅₀ = 3.9 μm, Except for using a BET specific surface area of 60 m ² / g), the same operation as in Example 1 was performed, and the powder catalyst of 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.

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

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

(Example 5)
Instead of the Nd solid solution zirconia composite oxide used in Example 1, NdLa solid solution zirconia composite oxide (Nd ₂ O ₃ : 26 mass%, La ₂ O ₃ : 8 mass%, ZrO ₂ : 66 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) And a sample for performance evaluation were obtained.

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

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

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

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

(Comparative Example 2)
Instead of the Nd solid solution zirconia composite oxide used in Example 1, Nd solid solution zirconia composite oxide (Nd ₂ O ₃ : 9% by mass, ZrO ₂ : 91% by mass: D ₅₀ = 2.5 μm, Except for using BET specific surface area: 65 m ² / g), the same operation as in Example 1 was performed, 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)
In place of the Nd solid solution zirconia composite oxide used in Example 1, Nd solid solution zirconia composite oxide (Nd ₂ O ₃ 18 mass%, ZrO ₂ : 82 mass%: D ₅₀ = 2.8 μm, BET Except for using a specific surface area of 64 m ² / g), the same operation as in Example 1 was performed, and the three-way catalyst for exhaust gas purification of Comparative Example 3 (supported amount in terms of Pd: 1.0 mass%) and performance evaluation A sample was obtained.

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

About the obtained sample for performance evaluation of Examples 1-8 and Comparative Examples 1-4, the palladium surface area and the BET specific surface area were measured, respectively. Table 1 shows the measurement results. Moreover, the 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, the three-way catalysts for exhaust gas purification of Examples 1 to 8 corresponding to the present invention were confirmed to have a larger palladium surface area than the three-way catalysts for exhaust gas purification of Comparative Examples 1 to 4. It was. It was also shown that the BET specific surface area tends to decrease as the amount of rare earth element solid solution increases. On the other hand, a clear correlation between the palladium surface area and the BET specific surface area could not be confirmed. This indicates that the number of catalytically active sites of the exhaust gas purification three-way catalyst is not necessarily proportional to the BET specific surface area, and the palladium surface area is large even if the BET specific surface area is relatively small. It was confirmed that a three-way catalyst for exhaust gas purification excellent in the above could 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. Here, a sample for performance evaluation that has been heat-treated in an oven in an air atmosphere at 800 ° C. for 20 hours is weighed 50 mg each and placed in a sample holder, and a TPD reactor (temperature desorption gas analyzer, trade name: BEL) The purification performance test was performed at 300 ° C. in a steady flow of model gas using Mass, manufactured by Microtrack Bell Co., Ltd.

Table 2 shows the model gas composition used here.

The HC purification rate and the NO purification rate were calculated based on the following formulas (2) and (3).
HC purification rate (%) = 100− (HC-MASS peak intensity (during measurement) / HC-MASS peak intensity (Blank)) × 100 (2)
NO purification rate (%) = 100− (NO-MASS peak intensity (during measurement) / NO-MASS peak intensity (Blank)) × 100 (3)

Table 3 shows the measurement results of the HC and NO purification performance.

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

  The exhaust gas purifying three-way catalyst and exhaust gas purifying catalytic converter 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 is more heat resistant than a diesel engine. Can be used particularly effectively in gasoline engine applications that require The exhaust gas purifying three-way catalyst of the present invention can be effectively used as a TWC for an engine direct catalytic converter, a tandem direct catalytic converter, or the like.

Claims (9)

Nd and Zr as constituent metal elements, the following mass ratios in terms of oxides:
ZrO ₂ 50-75% by mass;
Nd ₂ O ₃ 25-50% by mass;
Nd solid solution zirconia-based composite oxide base material particles,
Pd catalyst particles supported on the base material particles;
Containing at least
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 solution zirconia 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 oxides. Item 3. A three-way catalyst for purifying exhaust gas according to item 1 or 2. The Nd solid solution zirconia-based composite oxide has La as a constituent metal element and the following mass ratio in terms of oxide:
La ₂ O ₃ 0-18% by mass;
The three way catalyst for exhaust gas purification as described in any one of Claims 1-3 included in. The base material particles, the exhaust gas purifying three way catalyst according to claim 1 having an average particle diameter D ₅₀ of 1 to 100 [mu] m. The three-way catalyst for exhaust gas purification according to any one of claims 1 to 5, wherein a palladium surface area calculated by a carbon monoxide gas pulse adsorption method is 15 to 30 (m ² / Pd_g). The three-way catalyst for exhaust gas purification according to any one of claims 1 to 6, wherein the BET specific surface area is 10 to 50 (m ² / g). Nd and Zr as constituent metal elements, the following mass ratios in terms of oxides:
ZrO ₂ 50-75% by mass;
Nd ₂ O ₃ 25-50% by mass;
A step of preparing base material particles of Nd solute zirconia-based composite oxide contained in
A step of providing an aqueous solution containing at least Pd ions on the surface of the base material particles, and a step of supporting the Pd catalyst particles on the surface of the base material particles by heat-treating or chemically treating the base material particles after the treatment. , Characterized by having at least
A method for producing a three-way catalyst for exhaust gas purification. A catalyst carrier, an oxygen storage layer provided on the catalyst carrier, and a catalyst layer provided on the oxygen storage layer,
The catalyst layer includes the three-way catalyst for exhaust gas purification according to any one of claims 1 to 7,
Catalytic converter for exhaust gas purification.