Three-way catalyst and method for manufacturing the same

Abstract

The present invention provides a heat-resistant three-way catalyst that achieves both catalytic performance and OSC performance, as well as a method for manufacturing the same. [Solution] Some aspects of the present invention relate to a three-way catalyst comprising a precious metal, an OSC material, and an oxide solid solution containing barium and zirconium, wherein the precious metal is supported on the OSC material, the molar ratio (Ba:Zr) of barium to zirconium in the oxide solid solution is in the range of 20:80 to 49:51, and the content of barium carbonate and barium oxide in the oxide solid solution is 2% by weight or less, and a method for producing the same.

Description

Technical Field

[0001] Some aspects of the present invention relate to a three-way catalyst and a method for manufacturing the same.

Background Art

[0002] Exhaust gas discharged from internal combustion engines for automobiles or the like, for example, internal combustion engines such as gasoline engines or diesel engines, contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx).

[0003] Therefore, generally, an exhaust gas purification device for decomposing and removing these harmful components is provided in the internal combustion engine, and these harmful components are almost detoxified by an exhaust gas purification catalyst attached in the exhaust gas purification device, for example, a three-way catalyst.

[0004] The three-way catalyst contains a noble metal, and the noble metal plays a role in simultaneously promoting the oxidation reaction of CO and HC and the reduction reaction of NOx. Noble metals are expensive, and further reduction is required from the perspective of resource risk. In order to reduce the amount of noble metal, it is only necessary to prevent the catalytic activity of the noble metal from decreasing due to the use of the exhaust gas purification catalyst. In order to prevent the decrease in the catalytic activity of the noble metal, for example, suppression of poisoning of the noble metal by HC in the exhaust gas (HC poisoning), which is one of the factors causing the decrease in the catalytic activity of the noble metal, can be mentioned.

[0005] For example, Patent Document 1 discloses an exhaust gas purification catalyst characterized in that an active metal is supported on a carrier containing BaAl2O4 and BaZrO3.

[0006] Patent Document 2 includes, as main components, a catalyst A having an active metal α on the surface of a carrier a mainly composed of Ba, Al, and Zr and their oxides, and a catalyst B having an active metal β on the surface of a carrier b mainly composed of cerium oxide, and a mixing ratio of the mass of catalyst A to the total mass of catalyst A and catalyst B (A / (A + B)×100) is more than 10% by mass and less than 80% by mass. A mixed catalyst is disclosed.

[0007] Patent Document 3 describes an exhaust gas purification catalyst that is placed in the exhaust pipe of an internal combustion engine to purify the exhaust gas discharged from the internal combustion engine, comprising a substrate and a catalyst layer formed on the substrate, wherein the catalyst layer has an alkaline earth metal supported region comprising a porous carrier composed of an inorganic compound, Pt supported on the porous carrier, and a sulfate of at least one alkaline earth metal supported on the porous carrier, and a surface analysis by FE-EPMA is performed on the cross section of the alkaline earth metal supported region of the catalyst layer under the conditions of a pixel size of 0.34 μm × 0.34 μm and 256 × 256 measurement pixels, and the intensity of the characteristic X-ray of the alkaline earth metal element (Ae) (α: cps) and the intensity of the characteristic X-ray of Pt (β: cps) are measured for each pixel, and the Pearson correlation coefficient calculated using the obtained α and β for each pixel is R Ae / Pt In that case, the R Ae / Pt A catalyst for exhaust gas purification is disclosed, characterized in that the value of is 0.5 or greater.

[0008] Patent Document 4 discloses an exhaust gas purification catalyst characterized by containing a perovskite-type composite oxide composed of at least Ba, Zr, Y, and Pd. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2010-12459 [Patent Document 2] Japanese Patent Publication No. 2013-39520 [Patent Document 3] Japanese Patent Publication No. 2020-54982 [Patent Document 4] International Publication No. 2020 / 195600 [Overview of the project] [Problems that the invention aims to solve]

[0010] On the other hand, three-way catalysts are required to have oxygen storage capacity (OSC), and may include materials with OSC (OSC material) in addition to the catalytic metal. An "OSC material" is a material that can absorb and release oxygen. The OSC material helps maintain a constant oxygen concentration even when the air-fuel ratio fluctuates, thereby maintaining the purification performance (catalytic performance) of the three-way catalyst.

[0011] In other words, a desirable three-way catalyst is one that balances catalytic performance, specifically the suppression of HC poisoning of precious metals, with OSC performance.

[0012] However, in palladium (Pd)-based ternary catalysts, alkaline earth metals such as barium (Ba), including barium sulfate and barium carbonate, which can be introduced to suppress HC poisoning of precious metals and improve low-temperature activity, may migrate within the catalyst coating layer under certain high-temperature conditions and further react with OSC materials, such as CeO2-ZrO2 solid solutions (CZ), potentially degrading OSC performance. This is thought to be because the Ba supported on the surface of the support reacts with nearby OSC materials at high temperatures, reducing the crystallinity of the OSC materials. Furthermore, freed barium carbonate may reduce the specific surface area of ​​the support and substrate, and promote the covering of precious metals, potentially decreasing purification activity.

[0013] Therefore, some aspects of the present invention aim to provide a highly heat-resistant three-way catalyst that achieves both catalytic performance and OSC performance, and a method for producing the same. [Means for solving the problem]

[0014] The inventors investigated various means to solve the above-mentioned problems. The inventors found that by using a BaZrOx-based composite oxide (BZ) as a Ba additive in a three-way catalyst, the three-way catalyst becomes more thermally stable than when using BaCO3, BaO, and BaSO4, which were conventionally used as Ba additives, and furthermore, BaCO3 formation is less likely even at high temperatures. As a result, it is possible to achieve both OSC performance and purification activity after heat resistance testing of the three-way catalyst, and purification activity, especially at low temperatures. Furthermore, the inventors found that by limiting the ratio of Ba to Zr in the composition and structure of BZ to a specific range, the stability of the perovskite structure is higher than that of the BaZrMO3 system (wherein M is, for example, Y, Pd, Ce, etc.) which has a similar structure, and the formation of unstable BaCO3 and BaO can be suppressed. Based on the above, the inventors have completed several embodiments of the present invention.

[0015] In other words, the gist of some aspects of the present invention is as follows: (1) A three-way catalyst comprising a precious metal, an OSC material, and an oxide solid solution containing barium and zirconium, wherein the precious metal is supported on the OSC material, the molar ratio (Ba:Zr) of barium to zirconium in the oxide solid solution is in the range of 20:80 to 49:51, and the content of barium carbonate and barium oxide in the oxide solid solution is 2% by weight or less relative to the total weight of the oxide solid solution. (2) The ternary catalyst according to (1), wherein the oxide solid solution is a perovskite-type oxide. (3) The ternary catalyst according to (1) or (2), wherein the molar ratio (Ba:Zr) of barium to zirconium in the oxide solid solution is in the range of 30:70 to 49:51. (4) The three-way catalyst according to any one of (1) to (3), wherein the content of barium carbonate and barium oxide in the oxide solid solution is 1% by weight or less. (5) A method for manufacturing a three-way catalyst, comprising: (i) co-precipitating barium and zirconium from an aqueous solution containing a barium compound and a zirconium compound to obtain a precipitate, and firing the precipitate at 1000 °C to 1400 °C to prepare an oxide solid solution containing barium and zirconium, wherein the molar ratio of barium to zirconium (Ba:Zr) in the oxide solid solution is adjusted to be in the range of 20:80 to 49:51; (ii) mixing an aqueous solution containing a noble metal and an OSC material, and drying to prepare a noble metal-supported OSC material; and (iii) mixing the oxide solid solution prepared in (i) and the noble metal-supported OSC material prepared in (ii) to manufacture a three-way catalyst.

Advantages of the Invention

[0016] According to some aspects of the present invention, there are provided a high heat-resistant three-way catalyst that achieves both catalyst performance and OSC performance, and a method for manufacturing the same.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing the configuration of a three-way catalyst including a schematic diagram comparing the three-way catalysts of Comparative Examples 1 to 6 and the three-way catalysts of Examples 1 to 5. [Figure 2] It is a powder X-ray diffraction pattern of each Ba additive used in the examples and comparative examples. [Figure 3] It is a graph showing the relationship between the Ba / Zr molar ratio with respect to the Ba additive in the three-way catalysts of the examples and comparative examples and the amounts of barium carbonate and barium oxide. "Ex." indicates an example, and "Comp." indicates a comparative example. [Figure 4] It is a graph showing the relationship between the OSC amount at 500 °C and HC-T50 in the three-way catalysts of the examples and comparative examples. "Ex." indicates an example, and "Comp." indicates a comparative example. [[ID=2,6]]

Embodiments for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of some aspects of the present invention will be described in detail. This specification describes the features of several embodiments of the present invention with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of the parts are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of several embodiments of the present invention is not limited to the dimensions and shapes of the parts shown in these drawings. Furthermore, the three-way catalyst and the method for manufacturing the same according to several embodiments of the present invention are not limited to the following embodiments, and can be implemented in various forms with modifications, improvements, etc. that can be made by those skilled in the art without departing from the spirit of several embodiments of the present invention.

[0019] A ternary catalyst according to some aspects of the present invention comprises a noble metal, an OSC material, and an oxide solid solution containing barium and zirconium.

[0020] The precious metal is not limited as long as it acts as a catalytic metal. Examples of precious metals include gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), iridium (Ir), and mixtures of two or more of these. The precious metal may also be an alloy of two or more elements including the elements listed above. In one embodiment, the precious metal is Pt, Pd and / or Rh. In another embodiment, the precious metal is Pd.

[0021] The average particle size of the precious metal is not limited. The average particle size of the precious metal is typically 0.1 nm to 100 nm, and in one embodiment, 1 nm to 50 nm, as the equivalent diameter of the projection area circle (Haywood diameter) of a transmission electron microscope (TEM).

[0022] The precious metal content is not limited. The precious metal content is typically 0.1% to 20% by weight, and in one embodiment, 0.5% to 10% by weight, relative to the total weight of the three-way catalyst, in terms of precious metals. The content of components such as precious metals, OSC material, and oxide solid solutions containing barium and zirconium in the three-way catalyst usually depends on the amount of each component precursor added as material during the manufacture of the three-way catalyst.

[0023] By setting the type of precious metal, average particle size, and content as described above, sufficient catalytic performance of the three-way catalyst can be ensured.

[0024] OSC materials are not limited as long as they possess OSC properties. Examples of OSC materials include ceria (CeO2), alumina (Al2O3)-ceria-zirconia (ZrO2) composite oxides (ACZ), ceria-zirconia composite oxides (CZ), such as ceria-zirconia composite oxides having a fluorite structure (CeZrO4) or ceria-zirconia composite oxides having a pyrochlore structure (Ce2Zr2O7). Furthermore, the elemental composition ratios constituting the OSC material are not limited, and the OSC material may also contain additive elements such as praseodymium (Pr), scandium (Sc), yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), ytterbium (Yb), lutetium (Lu), titanium (Ti), and mixtures of two or more of these.

[0025] The average particle size of the OSC material is not limited. The average primary particle size of the OSC material is typically 1 nm to 50 nm, as measured by the equivalent diameter of the projected area circle (Heywood diameter) of a transmission electron microscope (TEM) or scanning electron microscope (SEM), and the average secondary particle size is 0.1 μm to 50 μm, or 1 μm to 25 μm in one embodiment.

[0026] The OSC material content is not limited, but is typically 5% to 80% by weight, and in one embodiment, 10% to 70% by weight, relative to the total weight of the three-way catalyst.

[0027] By setting the type, average particle size, and content of the OSC material as described above, sufficient OSC performance of the three-way catalyst can be ensured.

[0028] Barium and zirconium-containing oxide solid solutions are also referred to as BaZrOx-based composite oxides or BZ. Specifically, they include composite oxides having a BaZrO3-type perovskite structure and some monoclinic, tetragonal, and cubic ZrO2. The atomic molar ratio (Ba:Zr) of barium to zirconium in the BaZrOx-based composite oxide is adjusted to be in the range of 20:80 to 49:51, and in one embodiment to be in the range of 30:70 to 49:51.

[0029] In oxide solid solutions containing barium and zirconium, the content of barium carbonate (BaCO3) and barium oxide (BaO) is 2% by weight or less, 1.5% by weight or less in one embodiment, and 1% by weight or less in another embodiment, based on the total weight of the oxide solid solution. Since BaCO3 and BaO may not be present, the lower limit of the content of BaCO3 and BaO is not limited.

[0030] The presence of an oxide solid solution containing barium and zirconium in a barium-to-zirconium molar ratio within the aforementioned range allows for the stable maintenance of the perovskite structure by keeping the BaCO3 and BaO content within the aforementioned range without generating BaCO3 and BaO in the oxide solid solution, even under high-temperature atmospheres. As a result, the three-way catalyst can maintain high levels of both purification activity and OSC performance.

[0031] The average particle size of the oxide solid solution containing barium and zirconium is not limited. The average primary particle size of the oxide solid solution containing barium and zirconium is typically 10 nm to 80 nm, and in one embodiment, 1 nm to 50 nm, as the equivalent diameter of the projection area circle (Haywood diameter) of a transmission electron microscope (TEM).

[0032] The content of the oxide solid solution containing barium and zirconium is not limited, but is typically 5% to 40% by weight, and in one embodiment, 8% to 30% by weight, relative to the total weight of the three-way catalyst.

[0033] By setting the average particle size and content of the oxide solid solution containing barium and zirconium as described above, the HC poisoning of precious metals by barium can be sufficiently suppressed.

[0034] Three-way catalysts according to some embodiments of the present invention may further contain other components, to the extent that they do not impair the effects of the embodiments of the present invention.

[0035] Other components include metal oxides and additives used in three-way catalysts for this type of application, such as metal oxides, e.g., silica, magnesium oxide (MgO), zirconia, alumina, titania (TiO2), yttria (Y2O3), neodymium oxide (Nd2O3), lanthanum oxide (La2O3), composite oxides and solid solutions thereof, e.g., alumina-zirconia composite oxides (AZ), alkali metals, e.g., potassium (K), sodium (Na), lithium (Li), cesium (Cs), alkaline earth metals other than barium, e.g., calcium (Ca), strontium (Sr), rare earth elements, e.g., La, Y, Ce, etc., transition metals, e.g., iron (Fe), etc., and combinations of two or more of these. The ratio of each oxide in the composite oxide, e.g., AZ, is not limited and can be any ratio commonly used in the field of three-way catalyst technology.

[0036] The content of other components is not limited, but if present, it is typically 5% to 70% by weight, and in one embodiment, 10% to 50% by weight, relative to the total weight of the three-way catalyst.

[0037] Acidic supports, such as silica, are compatible with catalytic metals that reduce NOx. Basic supports, such as magnesium oxide, are compatible with potassium and barium, which absorb NOx. Zirconia suppresses sintering of other support particles at high temperatures where other support particles undergo sintering, and when combined with Rh as a noble metal, it can induce a steam reforming reaction to produce H2, thereby efficiently reducing NOx. Amphoteric supports, such as alumina, have a high specific surface area and can therefore be used to efficiently absorb and reduce NOx. Titania can suppress sulfur poisoning of catalytic metals. In addition, alumina, zirconia, and other metal oxides can increase the durability of the support when added.

[0038] In some embodiments of the present invention, the main support for the noble metal in the three-way catalyst is an OSC material, and some of the noble metal may also be supported on the Al2O3-based oxide support included in the three-way catalyst. By supporting the noble metal on the OSC material, the oxygen absorption and release performance can be fully exhibited, a high specific surface area can be secured as a support site for the noble metal, and as a result, high catalytic performance can be ensured.

[0039] Three-way catalysts according to some embodiments of the present invention can be used by filling them into a reaction tube or the like in pellet form.

[0040] Furthermore, some embodiments of the ternary catalyst of the present invention may, for practical purposes, have a substrate and a catalyst coating layer coated on the substrate, and may be used by introducing the following into the catalyst coating layer: a noble metal, an OSC material, an oxide solid solution containing barium and zirconium, and any other component.

[0041] When adopting such a three-way catalyst configuration, a known honeycomb-shaped substrate can be used as the substrate. Specifically, a honeycomb-shaped monolithic substrate (honeycomb filter, high-density honeycomb, etc.) can be used as the substrate. Furthermore, the material of such a substrate is not particularly limited. Examples of substrates include those made of ceramics such as cordierite, silicon carbide (SiC), silica (SiO2), alumina, mullite, or mixtures thereof, and substrates made of metals such as stainless steel containing chromium and aluminum. In one embodiment, the substrate is cordierite from a cost viewpoint.

[0042] The amount of catalyst coating layer is not limited, but is typically 100g to 300g per 1L of the volume of the portion of the substrate to which the catalyst coating layer is applied, and in one embodiment, it is 150g to 250g.

[0043] The thickness of the catalyst coating layer is not limited, but the average thickness is typically 50 μm to 200 μm, and in one embodiment, 80 μm to 150 μm. The thickness of the catalyst coating layer can be measured, for example, by a scanning electron microscope (SEM).

[0044] By ensuring that the amount and thickness of the catalyst coating layer are within the aforementioned range, a good balance between pressure loss, catalytic performance, and durability can be maintained in the three-way catalyst.

[0045] Some aspects of the present invention further relate to a method for producing a ternary catalyst according to some aspects of the present invention.

[0046] A ternary catalyst according to some aspects of the present invention can be manufactured by a method comprising: (i) preparing an oxide solid solution containing barium and zirconium by coprecipitating barium and zirconium from an aqueous solution containing a zirconium compound and a barium compound to obtain a precipitate, and calcining it at a specific temperature, wherein the molar ratio of barium to zirconium (Ba:Zr) in the oxide solid solution is adjusted to the range described above; (ii) preparing a noble metal-supported OSC material by mixing an aqueous solution containing a noble metal with an OSC material and drying it; and (iii) manufacturing a ternary catalyst by mixing the oxide solid solution prepared in (i) with the noble metal-supported OSC material prepared in (ii) and calcining it at a specific temperature.

[0047] In step (i), the type and concentration of the zirconium compound and the barium compound are not limited, as long as they dissolve in water as a solvent and the molar ratio of barium to zirconium is within the range described above. Examples of zirconium and barium compounds include acetates, nitrates, sulfates, halides, such as fluorides, chlorides, and bromides. The concentration of zirconium or barium in the aqueous solution containing the zirconium compound and the barium compound is usually in the range of 0.1 mol / L to 1.0 mol / L, respectively.

[0048] In step (i), the method for coprecipitation of barium and zirconium from aqueous solutions containing the zirconium compound and the barium compound is not limited. Examples of coprecipitation methods include mixing the aqueous solution containing the zirconium compound and the barium compound with an acid or base, adding the aqueous solution containing the zirconium compound and the barium compound to an acid or base, adding an acid or base to an aqueous solution containing the zirconium compound and the barium compound, and simultaneously adding the aqueous solution containing the zirconium compound and the barium compound with an acid or base to water. The acid or base is not limited. Examples of acids include hydrochloric acid, sulfuric acid, nitric acid, acetic acid, and mixtures of two or more of these. Examples of bases include sodium hydroxide, potassium hydroxide, ammonia, ammonium carbonate, ammonium bicarbonate, and mixtures of two or more of these. The reaction temperature is not limited, but is usually 20°C to 100°C, 20°C to 60°C in one embodiment, and 20°C to 40°C in one embodiment. The reaction time is not limited, but is typically 5 minutes to 2 hours, 10 minutes to 1 hour in one embodiment, and 20 minutes to 40 minutes in another embodiment.

[0049] The mixture containing barium and zirconium obtained by coprecipitation may optionally be dried, for example, at 100°C to 180°C for 1 to 10 hours, and then calcined, for example, at 300°C to 500°C for 1 to 8 hours.

[0050] The mixture containing barium and zirconium is then calcined at 1000°C to 1400°C, or 1100°C to 1200°C in one embodiment, for typically 1 to 20 hours, or 10 to 18 hours in one embodiment.

[0051] When a mixture containing barium and zirconium is calcined at a high temperature of 1000°C or higher, the mixture becomes a barium and zirconium oxide solid solution, i.e., a perovskite-type oxide.

[0052] In step (ii), the precious metals described above, OSC material, and other components are mixed together.

[0053] The mixing method is not limited. For example, one can use a method in which an aqueous solution of a dissolved precious metal is impregnated into the OSC material, or an aqueous solution of a dissolved precious metal is placed in the OSC material and then mixed.

[0054] The mixture of the precious metal and OSC material mixed in step (ii) is optionally dried, for example, usually at 100°C to 220°C for 1 to 15 hours, and then calcined, specifically at 400°C to 800°C, in one embodiment at 400°C to 600°C for 1 to 5 hours, to produce the precious metal-supported OSC material.

[0055] In step (iii), the oxide solid solution containing barium and zirconium prepared in (i) is mixed with the noble metal-supported OSC material prepared in (ii) and other components.

[0056] The mixing method is not limited. Examples of mixing methods include dry mixing and / or wet mixing.

[0057] The resulting mixture is optionally crushed and molded or shaped to produce a three-way catalyst.

[0058] Furthermore, in step (iii), the oxide solid solution containing barium and zirconium prepared in (i) and the noble metal-supported OSC material prepared in (ii) are mixed in a solvent, for example, water, to prepare a catalyst coating layer slurry. This catalyst coating layer slurry is then applied to the wall surface of the substrate as described above. The slurry is then dried, for example, usually at 100°C to 120°C for 1 to 3 hours, and further calcined, specifically at 400°C to 800°C, in one embodiment at 400°C to 600°C, and in one embodiment at 300°C to 500°C for 1 to 3 hours, thereby producing a ternary catalyst having a substrate and a catalyst coating layer coated on the substrate.

[0059] Furthermore, in steps (i) and (ii), the conditions described above, particularly those other than the firing temperature in step (i), are not limited. For example, the firing atmosphere may be in the atmosphere, or in an inert gas, such as nitrogen gas and / or a noble gas, such as argon gas.

[0060] (Applications of three-way catalysts) Three-way catalysts according to some aspects of the present invention can be highly effective in exhaust gas purification performance in rich atmospheres and can be used as heat-resistant three-way catalysts that exhibit a high HC poisoning suppression effect, even in environments where excess HC and other substances in a rich atmosphere can be adsorbed onto the three-way catalyst and poison the catalyst. [Examples]

[0061] The following describes some embodiments of the present invention, but it is not intended to limit the embodiments of the present invention to those shown in these embodiments.

[0062] 1. Preparation of the three-way catalyst Example 1 (BZ48 / 52) A barium acetate aqueous solution was prepared by dissolving 12.26 g of barium acetate in 100 g of deionized water and stirring for at least 15 minutes. Next, 20.67 g of 25% ammonia aqueous solution and 29.21 g of ammonium carbonate were dissolved in 200 g of deionized water and stirred for at least 15 minutes to prepare ammonia and ammonium carbonate aqueous solutions. Furthermore, a zirconyl oxynitrate aqueous solution was prepared by dissolving 35.60 g of zirconyl oxynitrate aqueous solution in 100 g of deionized water and stirring for at least 15 minutes.

[0063] Next, an aqueous solution of barium acetate and an aqueous solution of zirconyl oxynitrate were mixed, and the resulting aqueous solution was added dropwise to aqueous solutions of ammonia and ammonium carbonate under stirring with a stirrer, and then stirred for more than 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and then fired in air at 1100°C for 15 hours to obtain BaZrOx (Ba:Zr=48:52 molar ratio) powder (Ba additive). This was then crushed and sieved using a mortar and pestle to a size of 25 μm or less.

[0064] Next, 15.00 g of an Al2O3-CeO2-ZrO2 composite oxide (Al2O3:CeO2:ZrO2:La2O3:Y2O3=30:27:35:4:4 (weight ratio), hereinafter referred to as ACZ) was immersed in a palladium aqueous solution prepared by dissolving 1.83 g of palladium nitrate aqueous solution (8.2 wt%-equivalent to Pd) in 50 g of deionized water, and dried while stirring with a hot stirrer at 200°C. After that, it was dried overnight at 110°C and calcined in air at 500°C for 3 hours to obtain a Pd-supported ACZ catalyst. This was then crushed and sized using a mortar and pestle to a size of 25 μm or less.

[0065] Next, 12.0 g of pulverized Pd-supported ACZ and 2.0 g of BaZrOx powder were ground and mixed in a mortar for more than 5 minutes. The resulting powder was hydrostatically molded into a 1-ton volume and then sieved to form pellets with a diameter of 0.5 mm to 1.0 mm, which were used as the initial catalyst.

[0066] Example 2 (BZ45 / 55) In Example 1, the catalyst was prepared in the same manner as in Example 1, except that the BaZrOx (Ba:Zr=45:55 molar ratio) powder obtained as described below was used in place of the BaZrOx (Ba:Zr=48:52 molar ratio) powder.

[0067] 11.51 g of barium acetate was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous barium acetate solution. Next, 21.12 g of 25% aqueous ammonia solution and 29.83 g of ammonium carbonate were dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous ammonia and ammonium carbonate solutions. Furthermore, 37.71 g of aqueous zirconyl oxynitrate solution was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous zirconyl oxynitrate solution.

[0068] Next, an aqueous solution of barium acetate and an aqueous solution of zirconyl oxynitrate were mixed, and the resulting aqueous solution was added dropwise to aqueous solutions of ammonia and ammonium carbonate under stirring with a stirrer, and then stirred for more than 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and then fired in air at 1100°C for 15 hours to obtain BaZrOx (Ba:Zr = 45:55 molar ratio) powder.

[0069] Example 3 (BZ40 / 60) In Example 1, the catalyst was prepared in the same manner as in Example 1, except that the BaZrOx (Ba:Zr=40:60 molar ratio) powder obtained as described below was used in place of the BaZrOx (Ba:Zr=48:52 molar ratio) powder.

[0070] A barium acetate aqueous solution was prepared by dissolving 10.35 g of barium acetate in 100 g of deionized water and stirring for at least 15 minutes. Next, 22.04 g of 25% ammonia aqueous solution and 31.14 g of ammonium carbonate were dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare ammonia and ammonium carbonate aqueous solutions. Furthermore, a zirconyl oxynitrate aqueous solution was prepared by dissolving 41.60 g of zirconyl oxynitrate aqueous solution in 100 g of deionized water and stirring for at least 15 minutes.

[0071] Next, an aqueous solution of barium acetate and an aqueous solution of zirconyl oxynitrate were mixed, and the resulting aqueous solution was added dropwise to aqueous solutions of ammonia and ammonium carbonate under stirring with a stirrer, and then stirred for more than 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and then fired in air at 1100°C for 15 hours to obtain BaZrOx (Ba:Zr = 40:60 molar ratio) powder.

[0072] Example 4 (BZ30 / 70) In Example 1, the catalyst was prepared in the same manner as in Example 1, except that the BaZrOx (Ba:Zr=30:70 molar ratio) powder obtained as described below was used in place of the BaZrOx (Ba:Zr=48:52 molar ratio) powder.

[0073] A barium acetate aqueous solution was prepared by dissolving 7.66 g of barium acetate in 100 g of deionized water and stirring for at least 15 minutes. Next, 23.12 g of 25% ammonia aqueous solution and 32.67 g of ammonium carbonate were added to 100 g of deionized water and stirred for at least 15 minutes to prepare ammonia and ammonium carbonate aqueous solutions. Furthermore, a zirconyl oxynitrate aqueous solution was prepared by dissolving 47.92 g of zirconyl oxynitrate aqueous solution in 100 g of deionized water and stirring for at least 15 minutes.

[0074] Next, an aqueous solution of barium acetate and an aqueous solution of zirconyl oxynitrate were mixed, and the resulting aqueous solution was added dropwise to aqueous solutions of ammonia and ammonium carbonate under stirring with a stirrer, and then stirred for more than 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and then fired in air at 1100°C for 15 hours to obtain BaZrOx (Ba:Zr = 30:70 molar ratio) powder.

[0075] Example 5 (BZ20 / 80) In Example 1, the catalyst was prepared in the same manner as in Example 1, except that the BaZrOx (Ba:Zr=20:80 molar ratio) powder obtained as described below was used in place of the BaZrOx (Ba:Zr=48:52 molar ratio) powder.

[0076] 5.11 g of barium acetate was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous barium acetate solution. Next, 24.48 g of 25% aqueous ammonia solution and 34.59 g of ammonium carbonate were dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous ammonia and ammonium carbonate solutions. Furthermore, 54.76 g of aqueous zirconyl oxynitrate solution was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous zirconyl oxynitrate solution.

[0077] Next, an aqueous solution of barium acetate and an aqueous solution of zirconyl oxynitrate were mixed, and the resulting aqueous solution was added dropwise to aqueous solutions of ammonia and ammonium carbonate under stirring with a stirrer, and then stirred for more than 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and then fired in air at 1100°C for 15 hours to obtain BaZrOx (Ba:Zr = 20:80 molar ratio) powder.

[0078] Comparative example 1 (Pd / (BA+BZ)+Al2O3) 50.48 g of barium acetate was dissolved in 200 g of deionized water and stirred for at least 15 minutes. Then, 20 g of Al2O3 powder was added to the aqueous solution and stirred for another 15 minutes or more. After that, the mixture was evaporated to dryness while being heated and stirred with a hot stirrer. The resulting powder was dried overnight at 110°C, and then calcined in a muffle oven at 500°C for 5 hours. After that, it was ground and sizing to a particle size of 75 μm or less, and then calcined in a muffle oven at 1500°C for 10 hours to obtain BaAl2O4 powder.

[0079] Furthermore, 12.66 g of barium acetate was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous barium acetate solution. Next, 20.21 g of 25% aqueous ammonia solution and 28.56 g of ammonium carbonate were dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous ammonia and ammonium carbonate solutions. Finally, 33.91 g of aqueous zirconyl oxynitrate solution was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous zirconyl oxynitrate solution.

[0080] Next, an aqueous solution of barium acetate and an aqueous solution of zirconyl oxynitrate were mixed, and the resulting aqueous solution was added dropwise to aqueous solutions of ammonia and ammonium carbonate under stirring with a stirrer, and then stirred for more than 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and then fired in air at 1100°C for 15 hours to obtain BaZrO3 (Ba:Zr=50:50mol%) powder.

[0081] Subsequently, 9.0 g and 4.5 g of the obtained BaAl2O4 and BaZrO3 powders were taken and mixed, then ground and sized to a particle size of 25 μm or less. 9.0 g of the sized mixed powder was immersed in an aqueous solution prepared by mixing 1.10 g of palladium nitrate aqueous solution (8.2 wt% - equivalent to Pd) with 100 g of deionized water, and then dried at 200°C while stirring using a hot stirrer. The dried material was then further dried overnight at 110°C and calcined at 500°C in air for 3 hours to obtain Pd-supported BaAl2O4-BaZrO3 powder. 9.00 g of the obtained Pd-supported BaAl2O4-BaZrO3 powder and 1.00 g of Al2O3 powder (MI307) were mixed and ground and sized to a particle size of 25 μm or less. After that, it was hydrostatically molded at 1 ton and then sized into pellets of 0.5 mm to 1.0 mm.

[0082] Comparative Example 2 (BaZrYPdOx1:1.5:0.2:0.09) 9.15 g of barium acetate was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous barium acetate solution. Next, 21.40 g of 25% aqueous ammonia solution and 30.24 g of ammonium carbonate were dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous ammonia and ammonium carbonate solutions. Furthermore, 36.80 g of aqueous zirconyl oxynitrate solution, 2.75 g of yttrium nitrate hexahydrate, and 4.19 g of aqueous Pd nitrate solution (equivalent to 8.2% by weight of Pd) were dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous zirconyl oxynitrate, yttrium nitrate, and Pd nitrate solutions.

[0083] Next, an aqueous solution of barium acetate was mixed with an aqueous solution of zirconyl oxynitrate, yttrium nitrate, and Pd nitrate. The resulting aqueous solution was then added dropwise to an aqueous solution of ammonia and ammonium carbonate under stirring with a stirrer, and stirred for at least 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and finally fired in air at 1000°C for 1 hour to obtain BaZrYPdOx (Ba:Zr:Y:Pd = 1:1.5:0.2:0.09 molar ratio). This was then ground and sized using a mortar and pestle to a particle size of 25 μm or less.

[0084] Next, 15.00 g of Al2O3-CeO2-ZrO2 composite oxide (Al2O3:CeO2:ZrO2:La2O3:Y2O3=30:27:35:4:4 (weight ratio): hereinafter referred to as ACZ) was immersed in a palladium aqueous solution prepared by dissolving 1.83 g of palladium nitrate aqueous solution (8.2 wt%-equivalent to Pd) in 50 g of deionized water, and dried while stirring with a hot stirrer at 200°C. After that, the dried material was further dried overnight at 110°C and calcined in air at 500°C for 3 hours to obtain a Pd-supported ACZ catalyst. This was then crushed and sized using a mortar and pestle to a size of 25 μm or less. Next, 12.0 g of the crushed Pd-supported ACZ and 2.0 g of BaZrYPdOx powder were crushed and mixed in a mortar for more than 5 minutes. The mixed powder was subjected to 1 ton of hydrostatic molding, and then sieved to form pellets with a diameter of 0.5 mm to 1.0 mm, which served as the initial catalyst.

[0085] Comparative Example 3 (BaZrYPdOx1:1:0.2:0.09) In Comparative Example 2, the catalyst was prepared in the same manner as in Comparative Example 2, except that the BaZrYPdOx (Ba:Zr:Y:Pd=1:1:0.2:0.09 molar ratio) powder obtained as described below was used instead of the BaZrYPdOx (Ba:Zr:Y:Pd=1:1.5:0.2:0.09 molar ratio) powder.

[0086] 11.15 g of barium acetate was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous barium acetate solution. Next, 20.13 g of 25% aqueous ammonia solution and 28.45 g of ammonium carbonate were added to 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous ammonia and ammonium carbonate solutions. Furthermore, 29.89 g of aqueous zirconyl oxynitrate solution, 3.35 g of yttrium nitrate hexahydrate, and 5.10 g of aqueous Pd nitrate solution (equivalent to 8.2% by weight of Pd) were mixed with 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous solutions of zirconyl oxynitrate, yttrium nitrate, and Pd nitrate.

[0087] Next, an aqueous solution of barium acetate was mixed with an aqueous solution of zirconyl oxynitrate, yttrium nitrate, and Pd nitrate. The resulting aqueous solution was then added dropwise to an aqueous solution of ammonia and ammonium carbonate under stirring with a stirrer, and stirred for at least 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and finally fired in air at 1000°C for 1 hour to obtain BaZrYPdOx (Ba:Zr:Y:Pd = 1:1:0.2:0.09 molar ratio). This was then ground and sized using a mortar and pestle to a particle size of 25 μm or less.

[0088] Comparative Example 4 (BaZrCeOx1:0.9:0.1) In Comparative Example 2, the catalyst was prepared in the same manner as in Comparative Example 2, except that the BaZrCeOx (Ba:Zr:Ce=1:0.9:0.1 molar ratio) powder obtained as described below was used instead of the BaZrYPdOx (Ba:Zr:Y:Pd=1:1.5:0.2:0.09 molar ratio) powder.

[0089] A barium acetate aqueous solution was prepared by dissolving 12.77 g of barium acetate in 100 g of deionized water and stirring for at least 15 minutes. Next, an ammonia aqueous solution and an ammonium carbonate aqueous solution were prepared by dissolving 20.4 g of 25% ammonia aqueous solution and 28.45 g of ammonium carbonate in 100 g of deionized water and stirring for at least 15 minutes. Furthermore, an ammonia aqueous solution and an ammonium carbonate aqueous solution were prepared by dissolving 29.90 g of zirconyl nitrate aqueous solution and 2.17 g of cerium nitrate in 100 g of deionized water and stirring for at least 15 minutes.

[0090] Next, an aqueous solution of barium acetate was mixed with an aqueous solution of zirconyl oxynitrate and cerium ammonium nitrate. The resulting aqueous solution was then added dropwise to an aqueous solution of ammonia and ammonium carbonate under stirring with a stirrer, and stirred for at least 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and finally fired in air at 1000°C for 10 hours to obtain BaZrCeOx (Ba:Zr:Ce = 1:0.9:0.1 molar ratio) powder.

[0091] Comparative Example 5 (BZ55 / 45: Ba-rich) In Comparative Example 2, the catalyst was prepared in the same manner as in Comparative Example 2, except that the BaZrOx (Ba:Zr=55:45 molar ratio) powder obtained as described below was used instead of the BaZrYPdOx (Ba:Zr:Y:Pd=1:1.5:0.2:0.09 molar ratio) powder.

[0092] 14.05 g of barium acetate was dissolved in 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous barium acetate solution. Next, 19.72 g of 25% aqueous ammonia solution and 27.87 g of ammonium carbonate were added to 100 g of deionized water and stirred for at least 15 minutes to prepare aqueous ammonia and ammonium carbonate solutions. Furthermore, 30.81 g of aqueous zirconyl oxynitrate solution was mixed with 100 g of deionized water and stirred for at least 15 minutes to prepare an aqueous zirconyl oxynitrate solution.

[0093] Next, an aqueous solution of barium acetate and an aqueous solution of zirconyl oxynitrate were mixed, and the resulting aqueous solution was added dropwise to aqueous solutions of ammonia and ammonium carbonate under stirring with a stirrer, and then stirred for more than 30 minutes. The resulting sol was dried at 150°C for 8 hours, then calcined at 400°C for 5 hours, and then fired in air at 1100°C for 15 hours to obtain BaZrOx (Ba:Zr = 55:45 molar ratio) powder.

[0094] Comparative Example 6 (without Ba / ZLY only) In Comparative Example 2, the catalyst was prepared in the same manner as in Comparative Example 2, except that the ZrO2-La2O3-Y2O3 (ZrO2:La2O3:Y2O3 = 84:6:10 weight ratio) powder obtained as described below was used instead of the BaZrYPdOx (Ba:Zr:Y:Pd = 1:1.5:0.2:0.09 molar ratio) powder.

[0095] ZrO2-La2O3-Y2O3 (ZrO2:La2O3:Y2O3 = 84:6:10 by weight ratio) was calcined in air at 1100°C for 15 hours.

[0096] Figure 1 shows the configuration of a three-way catalyst, including a schematic diagram comparing the three-way catalysts of Comparative Examples 1-6 with those of Examples 1-5.

[0097] 2. Evaluation of the three-way catalyst X-ray diffraction test The diffraction lines of the powders of each Ba-additive used in the comparative example and the example were measured using a powder X-ray diffractometer (RINT-ULTIMA IV, Rigaku) ​​under the conditions of Cu-kα line 2θ = 20°~60°, 0.02° / step, scanning speed 5° / min, and 40V-40A. All diffraction patterns obtained were fitted using JADE-Pro (Lightstone), and the crystalline phases were identified and the BaCO3 and BaO phase contents were calculated.

[0098] Catalyst durability test 3.0 g of initial catalyst pellets with a diameter of 0.5 mm to 1.0 mm from the comparative examples and examples were packed into a quartz reaction tube with an inner diameter of 13 mm. Rich gas and lean gas as shown in the table below were alternately flowed through at a flow rate of 500 cc / min every 5 minutes, and a high-temperature endurance test was conducted at 1050°C for 25 hours.

[0099] [Table 1]

[0100] Evaluation of the oxygen absorption / release capacity (OSC) of catalysts After the catalyst durability test, 1.0 g of the catalyst was sealed in a 16 mmφ sample holder and set in a fixed-bed flow catalyst activity evaluation apparatus. The catalyst was pretreated at 500°C with alternating 2 vol. %-CO gas and 1 vol. %-O2 gas every 3 minutes. Then, at 400°C, the amount of CO2 produced when switching from lean gas to rich gas was measured to evaluate the oxygen absorption / desorption capacity (OSC) activity. The pretreatment and evaluation gases were as follows.

[0101] [Table 2]

[0102] Evaluation of catalyst purification activity (temperature characteristics) After the catalyst durability test, 1.0 g of the catalyst was sealed in a 16 mmφ quartz sample holder and set in a fixed-bed flow type catalyst activity evaluation apparatus (Best Instruments CATA5000). The catalyst was pretreated at 600°C, switching between pretreatment gases (rich gas and lean gas) every 10 seconds, then cooled, and the evaluation gas was flowed through while raising the temperature from 100°C to 550°C. The input gas temperature at which the HC and NOx purification rates reached 50% was evaluated as HC-T50 and NO-T50, respectively. The pretreatment and evaluation gases were as follows.

[0103] [Table 3]

[0104] Table 4 summarizes the compositions of the examples and comparative examples. Figure 2 shows the powder X-ray diffraction patterns of each Ba additive used in the examples and comparative examples. Furthermore, Figure 3 shows the relationship between the Ba / Zr molar ratio and the amounts of barium carbonate and barium oxide in the three-way catalysts of the examples and comparative examples. [Table 4]

[0105] Table 5 summarizes the activity evaluation results of the examples and comparative examples. Also, FIG. 4 shows the relationship between the OSC amount and HC-T50 at 500° C. in the three-way catalysts of the examples and comparative examples. Here, for the OSC amount, the larger the numerical value, the better, and for HC-T50 and NO-T50, the smaller the numerical value, the better.

Table 5

[0106] The addition of Ba to the Pd-based three-way catalyst suppresses the HC poisoning of Pd and improves the low-temperature activity of the three-way catalyst. However, as a problem (issue) of conventional Ba additives, CeO2-ZrO2 solid solution (CZ), which is responsible for the oxygen storage and release ability (OSC) essential for the three-way catalyst, and Ba undergo a solid-phase reaction, and the OSC performance after the durability test may decrease. In addition, the released barium carbonate may promote the decrease in the specific surface area of the carrier or substrate and the covering of the noble metal, and the purification activity may also decrease.

[0107] In some aspects of the present invention, by using a BaZrOx-based composite oxide as a Ba additive, a three-way catalyst can be obtained that is thermally more stable than BaCO3, BaO, and BaSO4, which are conventionally used Ba additives, and that achieves both OSC performance and purification activity that are less likely to form BaCO3 even after a heat resistance test. Further, in the BaZrOx-based composite oxide, when the composition and structure were adjusted so that 0.1 < Ba / Zr < 1, it was found that the stability of the perovskite structure was higher than that of the BaZrMO3-based with the same structure, and unstable BaCO3 and BaO were less likely to be generated, and a more stable Ba additive could be obtained.

[0108] The perovskite oxide composed of Ba and Zr has a tolerance factor of 1.006 indicating the stability of the perovskite structure and has a very stable perovskite structure. However, when an additive is introduced, the tolerance factor deviates greatly from 1, resulting in a decrease in stability. Also, if the Ba component becomes even slightly excessive, unstable free Ba components such as barium carbonate are generated. According to some aspects of the present invention, by slightly reducing the Ba / Zr ratio, even if free Ba is generated, the structure becomes such that it easily reacts with ZrO2. As a result, the generation of free Ba components that promote the deterioration of the three-way catalyst is suppressed, and the stability as a Ba additive can be improved. By mixing this BaZrOx composite oxide with a Pd catalyst containing an OSC material where 0.1 < Ba / Zr < 1, an exhaust gas purification catalyst excellent in OSC performance and purification activity can be realized.

[0109] In some aspects of the present invention, by using BaZrOx, which is a stable Ba additive, the generation of BaO and BaCO3, which are unstable Ba phases in a high-temperature atmosphere under the coexistence of H2O and CO2, is suppressed. As a result, the deterioration of the OSC is suppressed.

[0110] In some aspects of the present invention, by using BaZrOx, which is a stable Ba additive, the generation of BaO and BaCO3, which are unstable Ba phases in a high-temperature atmosphere under the coexistence of H2O and CO2, is suppressed, and the decrease in the specific surface area of the carrier or substrate and the covering of the noble metal are suppressed. As a result, the deterioration of the purification activity is suppressed.

Claims

1. A three-way catalyst comprising a precious metal, an OSC material, and an oxide solid solution containing barium and zirconium, The aforementioned precious metal is supported on the OSC material, The molar ratio (Ba:Zr) of barium to zirconium in the oxide solid solution is in the range of 20:80 to 49:

51. The content of barium carbonate and barium oxide in the oxide solid solution is 2% by weight or less relative to the total weight of the oxide solid solution. Three-way catalyst.

2. The ternary catalyst according to claim 1, wherein the oxide solid solution is a perovskite-type oxide.

3. The ternary catalyst according to claim 2, wherein the molar ratio (Ba:Zr) of barium to zirconium in the oxide solid solution is in the range of 30:70 to 49:

51.

4. The ternary catalyst according to any one of claims 1 to 3, wherein the content of barium carbonate and barium oxide in the oxide solid solution is 1% by weight or less.

5. A method for manufacturing a three-way catalyst, (i) A step of preparing an oxide solid solution containing barium and zirconium by coprecipitation of barium and zirconium from an aqueous solution containing a barium compound and a zirconium compound to obtain a precipitate, and calcining the precipitate at 1000°C to 1400°C. Here, the molar ratio (Ba:Zr) of barium and zirconium in the oxide solid solution is adjusted to a range of 20:80 to 49:

51. (ii) A step of preparing a precious metal-supported OSC material by mixing a precious metal-containing aqueous solution with an OSC material and drying it, (iii) A process to produce a three-way catalyst by mixing the oxide solid solution prepared in (i) with the noble metal-supported OSC material prepared in (ii) Methods that include...

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