Thermally stable oxygen storage material (OSM) and method for producing the same

Abstract

The present invention provides an oxygen storage material (OSM) comprising zirconium oxide, aluminum oxide, cerium oxide, and an oxide of at least one rare earth metal other than cerium. This oxygen storage material remains thermally stable without undergoing phase segregation or disproportionation after aging at 1,100°C for at least 6 hours.

Description

[Technical Field]

[0001] This disclosure generally relates to metal oxide materials, which are used as oxygen sensors, in solid oxide fuel cells, as catalysts, and in other applications requiring oxygen storage, high-speed oxygen transport, or conductivity. [Background technology]

[0002] The information in this section is provided solely for the purpose of providing background information related to this disclosure and does not constitute prior art.

[0003] In three-way catalysts (TWCs) or four-way catalysts, cerium-zirconium oxide materials are widely used as oxygen storage materials (OSMs). For success in this application, the OSM must exhibit high sintering resistance and high oxygen storage capacity over a wide temperature range (e.g., up to 1150°C), exhibit mesoporosity for effective mass transport properties, and be compatible with the incorporation of noble metals. Ease of oxygen transfer is a crucial requirement for such materials because both oxygen release and re-adsorption are necessary in the rapid transitions that occur in vehicle exhaust gases to prevent breakthrough of CO and HC (especially during vehicle acceleration).

[0004] The oxygen mobility in an oxygen storage material is determined by the interaction of multiple factors, including the oxide composition containing the type and amount of rare earth dopants present, the crystal phase (e.g., tetragonal phase, cubic phase, pyrochlore phase, etc.), surface area, porosity, crystallite size, etc. Extensive research on oxygen mobility in oxygen storage materials conducted over the past few decades has led to the development of materials that enable efficient operation of catalysts in the temperature range of 300 - 600 °C. Oxygen storage materials with high oxygen storage capacity make it possible to reduce the amount of oxygen storage material used, for example, by minimizing the thickness of the required oxygen storage material layer, reducing backpressure, and lowering the weight and cost associated with the catalytic converter of a vehicle.

[0005] However, CO, NO x , HC, and new stringent requirements regarding the emission levels of soot have made it necessary to search for new oxygen storage materials (OSMs), i.e., oxygen storage materials that exhibit high oxygen storage capacity, improved reducibility, long-term thermal stability, ease of reduction of CeO2, and easy oxygen movement within the lattice structure of the material. The development of such new oxygen storage materials is important not only for catalytic applications but also for use as electrolytes in solid oxide fuel cells (SOFCs) that also require high conductivity at low temperatures. SUMMARY OF THE INVENTION

[0006] The present disclosure generally relates to an oxygen storage material (OSM) that includes zirconium oxide, aluminum oxide, cerium oxide, and an oxide of at least one rare earth metal other than cerium, and the oxygen storage material remains thermally stable without any phase segregation or disproportionation occurring after aging at 1,100 °C for at least 6 hours.

[0007] When at least one rare earth metal contains yttrium, the CeO2 / ZrO2 molar ratio of the oxygen storage material is in the range of 0.20 to 1.50, or when yttrium is not present, it may be in the range of 0.40 to 1.50. The aluminum oxide (Al2O3) content of the oxygen storage material may be 40% by weight or less based on the total mass of the oxygen storage material. At least one rare earth metal oxide other than CeO2 in the oxygen storage material may be included up to 10% by weight based on the total mass of the oxygen storage material. The yttrium oxide (Y2O3) content of the oxygen storage material may be at least 0.5% by weight even if it is small based on the total mass of the oxygen storage material. When at least one rare earth metal contains yttrium, the CeO2 / ZrO2 molar ratio of the oxygen storage material may be in the range of 0.35 to 1.0, or when yttrium is not present, it may be in the range of 0.40 to 1.0.

[0008] According to another aspect of the present disclosure, after aging the oxygen storage material at 1,000 °C for 6 hours, it may have a specific surface area of 50 m 2 / g or more. Alternatively, after aging the oxygen storage material at 1,100 °C for 6 hours, it may have a specific surface area of 25 m 2 / g or more. When at least one rare earth metal contains yttrium, after aging the oxygen storage material in air at 1,200 °C, it remains thermally stable without any phase segregation and disproportionation occurring. The oxygen storage material exhibits an oxygen storage capacity (OSC) of 85% or more of the theoretical oxygen storage capacity.

[0009] According to yet another aspect of the present disclosure, a method for manufacturing a thermally stable oxygen storage material (OSM) is provided. This method includes (a) preparing an acidic solution containing polymeric zirconium oligomer; (b) mixing the acidic solution containing polymeric zirconium oligomer with an alumina source to form a mixture; (c) mixing a complexing agent into the mixture; (d) allowing the mixture to stand to form a zirconium-aluminum-based precursor; (e) Adding a base to the zirconium-aluminum precursor to neutralize the zirconium-aluminum precursor and form a zirconium-aluminum hydrated oxide slurry, (f) A zirconium-aluminum hydrated oxide slurry is mixed with an acidic solution containing cerium and at least one rare earth metal other than cerium to form a polyvalent metal-containing slurry. (g) A step of aging the polyvalent metal-containing slurry at a pH higher than 10 in order to enable the formation of a mixed hydrated oxide precipitate, (h) Washing the mixed hydrated oxide precipitate to remove the anionic mixture, the cationic mixture, or both; (i) A step of drying the washed mixed hydrated oxide precipitate, (j) The step of calcining the dried mixed hydrated oxide precipitate to form an oxygen storage material (OSM) Includes. The oxygen storage material produced by this method is thermally stable after aging at 1,100°C for at least 6 hours, without undergoing either phase segregation or disproportionation.

[0010] In this method, at least one rare earth metal other than cerium may include yttrium. The polymerized zirconium oligomer may contain zirconium octamers in an amount ranging from 30% to 100% by mass relative to the mass of the polymerized zirconium oligomer. The polymerized zirconium oligomer generally does not contain any zirconia sol particles. The base may be an alkali metal hydroxide, aqueous ammonia, or both.

[0011] The aluminum source may contain one or more selected from the group consisting of dispersible aluminum hydroxide, dispersible boehmite, aluminum oxide, aluminum Keggin-type ion nanoclusters, and combinations thereof. If aluminum Keggin-type ion nanoclusters are present, their amount may be 25% by weight or more relative to the total aluminum content of the aluminum source.

[0012] The complexing agent may be selected from the group consisting of sulfates, persulfates, oxalates, succinates, and combinations thereof. The amount of complexing agent added to the zirconium-aluminum acid mixture is usually in the range of 0.4 to 1.2 moles per mole of zirconium.

[0013] Acidic solutions containing polymerized zirconium oligomers, and acidic solutions containing cerium and at least one rare earth metal other than cerium, may be formed using water-soluble compounds of zirconium, cerium, and at least one rare earth metal other than cerium, in the form of nitrates, chlorides, sulfates, acetates, or combinations thereof.

[0014] Further applicable areas will become apparent from the descriptions provided herein. The descriptions and specific examples are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0015] In the following sections, various forms of the disclosure described herein will be explained with reference to the attached drawings, so that the disclosure may be fully understood. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a flowchart illustrating a method for preparing a thermally stable oxygen storage material (OSM) according to the teachings of this disclosure. [Figure 2A] Figure 2A is a graphical representation of the X-ray diffraction (XRD) spectra of a thermally stable oxygen storage material prepared according to the teachings of this disclosure, measured after thermal aging at 1,100°C and 1,200°C for 6 hours. [Figure 2B] Figure 2B is a graphical representation of the X-ray diffraction (XRD) spectra of a thermally stable oxygen storage material prepared according to the teachings of this disclosure, measured after thermal aging at 1,100°C and 1,200°C for 6 hours. [Figure 3]Figures 3A and 3B are graphical representations of the X-ray diffraction (XRD) spectra of another thermally stable oxygen storage material prepared according to the teachings of this disclosure, measured after thermal aging of this oxygen storage material at 1,100°C and 1,200°C for 6 hours, respectively. [Figure 4] For yet another thermally stable oxygen storage material prepared according to the teachings of this disclosure, Figures 4A and 4B are graphical representations of the X-ray diffraction (XRD) spectra measured after thermal aging of this oxygen storage material at 1,100°C and 1,200°C for 6 hours, respectively. [Figure 5] For yet another thermally stable oxygen storage material prepared according to the teachings of this disclosure, Figures 5A and 5B are graphical representations of the X-ray diffraction (XRD) spectra measured after thermal aging of this oxygen storage material at 1,100°C and 1,200°C for 6 hours, respectively. [Figure 6] Figures 6A and 6B show graphs of the X-ray diffraction (XRD) spectra of the oxygen storage material used for comparison, measured after thermal aging at 1,100°C and 1,200°C for 6 hours, respectively. [Modes for carrying out the invention]

[0017] The drawings included herein are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0018] The following descriptions are essentially illustrative and are not intended in any way to limit the disclosure or its application or use. For example, oxygen storage materials (OSMs) prepared and used in accordance with the teachings contained herein are described throughout this disclosure together with three-way catalytic converters (TWCs) used to reduce vehicle emissions, in order to more fully explain their composition and applications. HC, CO, NO from gasoline or diesel engines. xThe incorporation and use of such oxygen storage materials in other catalysts for removing soot, diesel oxidation catalysts, and other oxidation catalysts, or in other applications such as oxygen sensors or electrolytes used in solid oxide fuel cells (SOFCs), is considered to be within the scope of this disclosure. Throughout this description, please understand that corresponding reference numerals indicate similar or corresponding parts and features.

[0019] This disclosure generally provides an oxygen storage material that remains thermally stable after aging at 1,100°C without undergoing either phase segregation or disproportionation. The oxygen storage material may contain, be composed of, or be essentially composed of oxides of zirconium oxide, aluminum oxide, cerium oxide, and at least one rare earth metal other than cerium. The material of the oxygen storage material may be cerium oxide and zirconium oxide, thereby exhibiting a molar ratio of cerium oxide to zirconium oxide between about 0.20 and about 1.50, or between 0.35 and 1.00, provided that at least one rare earth metal present in the composition contains yttrium. If yttrium is not present, the CeO2:ZrO2 molar ratio is in the range of 0.40 to 1.50, or between 0.40 and 1.00.

[0020] For the purposes of this disclosure, the terms “at least one” and “one or more of” are to be used interchangeably and may have the same meaning. These terms, which refer to including a singular or plural element, may also be expressed with the suffix “(plural)” at the end of the element. For example, “at least one rare earth metal,” “one or more rare earth metals,” and “rare earth metals (plural)” may be used interchangeably and are intended to have the same meaning.

[0021] Furthermore, abbreviations such as OSM are used interchangeably in this specification. These abbreviations are intended to convey the same meaning whether they refer to a single oxygen storage material or multiple oxygen storage materials.

[0022] For the purposes of this disclosure, the terms “about” and “substantially” are used herein in reference to measurable values ​​and ranges, which are due to expected variations known to those skilled in the art (e.g., limits and variability in measurement).

[0023] The aluminum oxide content (Al2O3) of the oxygen storage material (OSM) is 40% by weight or less relative to the total mass of the oxygen storage material. Where desirable, the aluminum oxide content of the oxygen storage material may be in the range of approximately 30% to 40% by weight, or approximately 30% to 35% by weight, or approximately 30% by weight, relative to the total weight of the oxygen storage material.

[0024] According to another aspect of this disclosure, at least one rare earth metal oxide other than cerium oxide is included in the oxygen storage material (OSM) in an amount up to 15% by weight or up to 10% by weight relative to the total mass of the oxygen storage material. Alternatively, at least one rare earth metal oxide other than CeO2 is included in an amount ranging from about 5% to 11% by weight, or from about 7% to about 10% by weight, or from about 7.5% by weight relative to the total mass of the oxygen storage material.

[0025] When yttrium oxide is present as a rare earth metal oxide other than cerium oxide in an oxygen storage material, the yttrium oxide (Y2O3) content is at least 0.50 wt%, or between 1 wt% and 5 wt%, or between 2 wt% and 3 wt%, or up to 5 wt%.

[0026] The cerium oxide content in the oxygen storage material (OSM) may be in the range of 15% to 35% by weight, or about 20% to 30% by weight, or about 22% to 29% by weight, relative to the total mass of the oxygen storage material.

[0027] The zirconium oxide content in the oxygen storage material may be in the range of approximately 25% to 50% by weight, or approximately 30% to 45% by weight, or approximately 33% to 42% by weight, relative to the total mass of the oxygen storage material.

[0028] For the purposes of this disclosure, the term "weight" refers to a mass value having units such as grams or kilograms. Furthermore, the description of a numerical range by an endpoint includes all numbers within that endpoint and its numerical range. For example, a quantity in the range of 40% by weight to 60% by weight (also written as 40% by weight to 60% by weight) includes concentrations of 40% by weight, 60% by weight, and all concentrations in between (e.g., 40.1%, 41%, 45%, 50%, 52.5%, 55%, 59%, etc.).

[0029] According to another aspect of this disclosure, the at least one rare earth metal other than cerium (Ce) present in the oxygen storage material (OSM) may include dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), yttrium (Y), or a mixture thereof. Alternatively, the rare earth metal other than cerium present in the oxygen storage material may be selected from the group consisting of lanthanum, neodymium, praseodymium, yttrium, or combinations thereof. The amount of rare earth metal present in the oxygen storage material is sufficient to stabilize the crystal lattice of the material.

[0030] JPEG2026511506000002.jpg32170

[0031] Cerium oxide is a non-stoichiometric CeO 2-x It has the ability to form surface defect sites, which leads to the formation of oxygen vacancies and active surface oxygen species. Zirconium oxide exhibits a similar effect. When both cerium oxide and zirconium oxide are combined to form an oxygen storage material, this effect is enhanced. In addition to surface oxygen mobility, zirconium oxide is Ce 4+ From Ce 3+An increase in reducibility also causes an increase in the mobility of lattice oxygen species. The introduction of zirconium oxide into the cubic cerium oxide lattice increases the generation of defects in the cerium-zirconium oxide-based oxygen storage material, which promotes the mobility of lattice oxygen, thereby enabling the redox reaction occurring on the surface to also occur inside the oxygen storage material. Zirconium oxide also has the ability to stabilize the crystal structure during high-temperature use.

[0032] The oxygen storage material (OSM) may exhibit a specific surface area (SSA) of 50 m 2 / g or more after aging at 1,000 °C for 6 hours, or the specific surface area may be in the range of 50 m 2 / g to about 75 m 2 / g, or in the range of 50 m 2 / g to about 60 m 2 / g. When aged at 1,100 °C for 6 hours, the specific surface area is 25 m 2 / g or more, or the specific surface area is in the range of about 25 m 2 / g to 49 m 2 / g, or the specific surface area is in the range of 25 m 2 / g to about 45 m 2 / g, or the specific surface area is in the range of 25 m 2 / g to about 40 m 2 / g. After aging at 1,200 °C for 6 hours, the specific surface area is 10 m 2 / g or more, or the specific surface area is in the range of about 10 m 2 / g to about 24 m 2 / g, or the specific surface area is in the range of 10 m 2 / g to about 20 m 2 / g, or in the range of 10 m 2 / g to about 16 m 2 / g.

[0033] The oxygen storage material (oxygen storage material) may exhibit a pore volume (PV) of 0.400 cm 3 / g or more after aging at 1,000 °C for 6 hours, or the pore volume may be in the range of 0.420 cm 3 / g to about 0.600 cm3 / g, or 0.430cm 3 / g ~ approx. 0.550cm 3 The range is / g. After aging at 1,100°C for 6 hours, the pore volume is 0.200 cm³. 3 The amount is greater than or equal to / g, or the pore volume is approximately 0.210 cm³. 3 / g~0.450cm 3 The range is / g, or the pore volume is 0.220 cm³. 3 / g ~ approx. 0.400cm 3 The range is / g, or the pore volume is 0.225 cm³. 3 / g ~ approx. 0.385cm 3 The range is / g. After aging at 1,200°C for 6 hours, the pore volume is 0.075 cm³. 3 The amount is greater than or equal to / g, or the pore volume is approximately 0.080 cm³. 3 / g ~ approx. 0.120cm 3 The range is / g, or the pore volume is 0.080 cm³. 3 / g ~ approx. 0.1150cm 3 It is within the range of / g.

[0034] Oxygen storage materials (OSMs) formed according to the teachings of this disclosure remain thermally stable after aging at 1,100°C for at least 6 hours, without any phase segregation or disproportionation. If at least one rare earth metal oxide other than cerium oxide is yttrium oxide, the thermal stability is further improved, with no phase segregation or disproportionation present or only beginning to occur after aging at 1,200°C.

[0035] According to another aspect of this disclosure, the oxygen storage material of this disclosure exhibits high redox activity. The oxygen storage material can take in oxygen from an oxidizing atmosphere and supply oxygen in a reducing atmosphere. This property is called the oxygen storage capacity (OSC) of the material. More specifically, the oxygen storage capacity can be defined as the amount of oxygen absorbed by the oxygen storage material and released from the oxygen storage material per unit weight of the oxygen storage material on a timescale of several seconds to several minutes. The oxygen storage capacity (OSC) of the oxygen storage material of this disclosure is at least 80% of the theoretical oxygen storage capacity of a given material composition, or the oxygen storage capacity of the oxygen storage material is 85% or more of the theoretical oxygen storage capacity, or the oxygen storage capacity is 90% or more of the theoretical oxygen storage capacity.

[0036] Another embodiment of this disclosure provides a method for preparing a thermally stable oxygen storage material (OSM) as defined above and further in this section. Referring to Figure 1, Method 1 is generally, (a) Step 5 involves preparing an acidic solution containing polymerized zirconium oligomer, (b) Step 10, in which an acidic solution containing polymerized zirconium oligomer and an alumina source are mixed to form a mixture, (c) Step 15 of mixing the complexing agent into the mixture, (d) Step 20, in which the mixture is left to stand to form a zirconium-aluminum precursor, (e) Step 25, in which a base is added to the zirconium-aluminum precursor to neutralize the zirconium-aluminum precursor and form a zirconium-aluminum hydrated oxide slurry, (f) Step 30, in which a zirconium-aluminum hydrated oxide slurry is mixed with an acidic solution containing cerium and at least one rare earth metal other than cerium to form a polyvalent metal-containing slurry, (g) Step 35 involves aging the polyvalent metal-containing slurry at a pH higher than 10 in order to enable the formation of a mixed hydrated oxide precipitate, (h) step 40, washing the mixed hydrated oxide precipitate to remove the anionic mixture or the cationic mixture or both, (i) step 45, drying the washed mixed hydrated oxide precipitate, (j) Calcining the dried mixed hydrated oxide precipitate to form an oxygen storage material (OSM) in step 50. The oxygen storage material, after aging at 1,100°C, is thermally stable without any phase segregation or disproportionation.

[0037] Referring here to a specific embodiment of Method 1 shown in Figure 1, the acidic solution initially prepared (Step 5) to be a solution containing polymerized zirconium oligomers contains such oligomers in an amount ranging from about 30% to about 100% by weight of the total weight of the solution. Alternatively, the polymerized zirconium oligomers may be present in an amount ranging from 35% to about 90% by weight, or in an amount ranging from 40% to about 80% by weight, or in an amount greater than 30% by weight, or in an amount greater than 50% by weight, or in an amount greater than 75% by weight.

[0038] Acidic solutions of polymerized zirconium oligomers may be prepared by any known method (Step 5). These methods include, but are not limited to, partial removal of charge equilibrium counteranions by electrodialysis, anion extraction by treatment with aliphatic amines or anion exchange resins, dissolution of freshly prepared zirconium hydroxide in acid, or utilization of the redox reaction between the zirconium oxychloride solution and chloride ions of H2O2 in an acidic medium. When polymerized zirconium species are used as the zirconium source, the starting block in zirconia nucleation changes to varying degrees from zirconium tetramer units (in the case of zirconium oxychloride) to zirconium oligomer species (e.g., octamers), increasing the average nucleus size and altering its morphology. Preferably, the polymerized zirconium oligomer may contain zirconium octamers in the range of about 30–100% or about 40–90% relative to the total mass of the polymerized zirconium oligomer. Polymerized zirconium oligomers do not contain zirconia sol particles.

[0039] Continuing to refer to Figure 1, the alumina source mixed with the acidic solution of polymerized zirconium oligomer (step 10) contains one or more selected from the group consisting of dispersible aluminum hydroxide, dispersible boehmite, aluminum oxide, aluminum Keggin-type ion nanoclusters, and combinations thereof. Alternatively, the alumina source contains aluminum Keggin-type ion nanoclusters in an amount of 25% by weight or more relative to the total aluminum content of the alumina source. Alternatively, the amount of aluminum Keggin-type ion nanoclusters present in the alumina source is in the range of 25% by weight to about 35% by weight.

[0040] Dispersible boehmite is a powder in which boehmite particles form a stable nano-sized dispersion in a desired or selected fluid such as water or an organic solvent. Keggin-type aluminum ion nanoclusters, also known as polyaluminum (oxy) hydroxide nanoclusters, may contain various isomers and different surface functional groups. Among many possible examples, one example of a Keggin-type aluminum ion nanocluster is [AlO4Al 12 (OH) 24 (H2O) 12 ] 7+ (Al 13 This includes, but is not limited to, this Al. 13 Keggin clusters generally contain a tetrahedral Al(O)4 unit surrounded by 12 Al octahedra, held within four [Al3(μ2-OH)6(H2O)3] trimers. 13 Nanoclusters are formed, for example, through condensation reactions and the addition of monomeric aluminum crosslinking molecules, such as [Al2(O)8Al 24 (OH) 50 (H2O) 20 ] 12+ (Al 26 ), [Al 30 (O)8(OH) 56 (H2O) 24 ] 18+ (Al 30 ), and [Al 32 (O)8(OH) 60 (H2O) 28 (SO4)2] 16+ (Al 32 Larger nanoclusters such as ) may be formed.

[0041] Another aspect of Method 1 includes adding a complexing agent to the reaction mixture (Step 15). This complexing agent may contain an anion having affinity for zirconium. The complexing agent may be selected from the group comprising sulfates, persulfates, oxalates, succinates, and combinations thereof, or the group consisting of, or essentially consisting of. The complexing agent is selected to adsorb onto the surface of the zirconium oligomer, thereby occupying and protecting the reactive sites from participation in further polymerization reactions. The amount of complexing agent added to the reaction mixture (Step 15) may be in the range of 0.4 to 1.2 moles per mole of zirconium present in the reaction mixture. Alternatively, the amount of complexing agent may be in the range of 0.4 to 1.0 mole per mole of zirconium, or between 0.50 and 0.80 moles per mole of zirconium. As a result, during the neutralization reaction (step 25) (e.g., addition of a base), competition from hydroxide ions causes the complexing agent to delay the formation of zirconium hydroxide primary particles, influencing their size, morphology, and packing method (e.g., enabling the formation of loosely assembled secondary aggregates).

[0042] Continuing to refer to Figure 1, the preparation (step 5) of the acidic solution containing polymerized zirconium oligomer and the acidic solution containing cerium and at least one rare earth metal other than cerium (which will later be mixed with the zirconium-aluminum precursor (step 30)) is carried out using water-soluble compounds of zirconium, cerium, and at least one rare earth metal other than cerium. These water-soluble compounds may be in the form of nitrates or chlorides or sulfates or acetates or combinations thereof.

[0043] Furthermore, the base added to form the zirconium-aluminum hydrated oxide slurry (step 25) may be selected from alkali metal hydroxides, aqueous ammonia, tetraalkylammonium hydroxide, or a combination thereof. Alternatively, the base may be an alkali metal hydroxide, aqueous ammonia, or both.

[0044] The specific examples presented below are for illustrative purposes only and should not be construed as limiting the scope of the disclosure, but rather to illustrate oxygen storage materials (OSMs) conforming to the teachings of this disclosure, their properties, and methods for producing them. Those skilled in the art will understand, in view of this disclosure, that many modifications can be made to the specific embodiments disclosed herein without departing from or exceeding the spirit or scope of this disclosure, and that similar or comparable results can still be obtained. Those skilled in the art will further understand that all properties reported herein represent properties that are typically measured and can be obtained in multiple different ways. The methods described herein represent one such method, and using other methods will not exceed the scope of the disclosure.

[0045] Test method The specific surface area (SSA) and pore volume (PV) of oxygen storage materials are measured using the conventional Brunauer-Emmett-Teller (BET) method and the Barrett-Joyner-Hallenda (BJH) method, both using a TriStar analyzer manufactured by Micromeritics.

[0046] The crystalline phase or skeletal structure of zeolites may be characterized by X-ray diffraction (XRD) data. However, XRD measurements can be affected by various factors, such as the growth direction of the zeolite, the ratio of constituent elements, the presence of adsorbed substances and defects, and the intensity ratio or positional shift of each peak in the X-ray diffraction spectrum. Therefore, deviations of 10% or less, 5% or less, or 1% or less in the measured values ​​for each parameter of the zeolite skeletal structure are within the expected acceptable range.

[0047] The redox activity of aged oxygen storage materials is tested using the conventional TPR-H2 method. The TPR-H2 method is a measurement method that can indicate the amount of reactive oxygen species and the steps in the reduction process of metal oxides. Using a Micromeritics Autochem II 2920 instrument, the temperature is increased at 10°C / min in the temperature range from 25°C to 900°C, and the sample is taken at 5 cm. 3A temperature-induced reduction (TPR) test is performed at a constant flow rate of 90% Ar / 10% H2 gas per minute.

[0048] Example 1 A thermally stable oxygen storage material is prepared according to the following procedure. The composition of this oxygen storage material is 30% Al2O3, 22% CeO2, 37.5% ZrO2, 5% La2O3, 3% Y2O3, and 2.5% Nd2O3, with a CeO2 / ZrO2 molar ratio of 0.42.

[0049] A zirconium-containing solution is prepared by dissolving 50.5 grams of ZrOCl2·8H2O crystals in 400 grams of deionized (DI) water. 32.4 grams of 15% NaOH solution are added to the zirconium-containing solution and mixed until a clear solution of polymerized zirconium precursor is formed. Next, 15.0 grams of alumina slurry consisting of boehmite and Keggin-type aluminum nanoclusters (ratio 4:1) is added to the zirconium-containing solution. Then, 64.2 grams of 16.7% Na2SO4 solution are added to the zirconium-containing solution to form a zirconium-alumina precursor. 141 grams of 7.8% Ce(NO3)3 solution, 16.1 grams of 15.5% La(NO3)3 solution, 7.6 grams of 19.75% Y(NO3)3 solution, and 5.2 grams of 24.1% Nd(NO3)3 solution are added to the zirconium-alumina precursor and mixed thoroughly to form a slurry. Finally, slowly add the 25% NaOH solution to the slurry until the pH reaches 13. Age the slurry while maintaining the pH above 10 until a precipitate forms. Filter the formed precipitate using a Buchner funnel and wash with deionized (DI) water to remove excess cations, anions, or both. Dry the resulting precipitate, e.g., wet cake, in an electric oven at 130°C, then bake at 700°C for 2 hours to form a powder containing oxygen storage material (OSM).

[0050] The calcined oxygen storage powder was aged for an additional 6 hours at temperatures of 1,000°C, 1,100°C, and 1,200°C. No signs of the presence of an alumina phase or disproportionation were observed in the oxygen storage material after aging at any of the above predetermined temperatures. The X-ray diffraction (XRD) spectra measured for the oxygen storage material after aging at 1,100°C for 6 hours and 1,200°C for 6 hours are shown in Figures 2A and 2B. These spectra in Figures 2A and 2B indicate that the oxygen storage material maintains phase stability even after exposure to such thermal aging conditions.

[0051] The TPR-H2 profile of this oxygen storage material was measured and found to represent more than 85% of the theoretical oxygen storage capacity (OSC) available to the material. The specific surface area (SSA) and pore volume (PV) of the oxygen storage material after firing were similarly measured after aging at predetermined temperatures. A summary of these results is shown in Table 1.

[0052] [Table 1]

[0053] This embodiment demonstrates that an oxygen storage material formed according to the teachings of this disclosure remains thermally stable after aging at 1,100°C without undergoing either phase segregation or disproportionation. Furthermore, the inclusion of yttrium oxide in this composition further improves the thermal stability of the oxygen storage material, as neither phase segregation nor disproportionation occurs even after aging at 1,200°C for at least 6 hours.

[0054] Example 2 A thermally stable oxygen storage material is prepared according to the following procedure. The composition of this oxygen storage material is 30% Al2O3, 22% CeO2, 40.5% ZrO2, 4% La2O3, 2.5% Y2O3, and 1% Nd2O3, with a CeO2 / ZrO2 molar ratio of 0.39.

[0055] A zirconium-containing solution is prepared by dissolving 54.6 grams of ZrOCl2·8H2O crystals in 460 grams of deionized (DI) water. 35.0 grams of 15% NaOH solution is added to the zirconium-containing solution and mixed until a clear solution of polymerized zirconium precursor is formed. Then, 15.0 grams of alumina slurry consisting of boehmite and Keggin-type aluminum nanoclusters (ratio 4:1) is added to the zirconium-containing solution. Next, 69.4 grams of 16.7% Na2SO4 solution is added to the zirconium-containing solution to form a zirconium-alumina precursor. 125.9 grams of 8.7% Ce(NO3)3 solution, 12.9 grams of 15.5% La(NO3)3 solution, 6.3 grams of 19.75% Y(NO3)3 solution, and 2.1 grams of 24.1% Nd(NO3)3 solution are added to the zirconium-alumina precursor and mixed thoroughly. Finally, slowly add the 25% NaOH solution to the slurry until the pH reaches 13. Age the slurry while maintaining the pH above 10 until a precipitate forms. Filter the formed precipitate using a Buchner funnel and wash with deionized (DI) water to remove excess cations, anions, or both. Dry the resulting precipitate, e.g., wet cake, in an electric oven at 130°C, then bake at 700°C for 2 hours to form a powder containing oxygen storage material (OSM).

[0056] The calcined oxygen storage powder was aged for an additional 6 hours at temperatures of 1,000°C, 1,100°C, and 1,200°C, respectively. No signs of the presence of an alumina phase or disproportionation were observed in the oxygen storage material after aging at 1,000°C or 1,100°C. Figures 3A and 3B show the X-ray diffraction (XRD) spectra measured for the oxygen storage material after aging at 1,100°C for 6 hours and 1,200°C for 6 hours. The X-ray diffraction spectrum shown in Figure 3A indicates that the oxygen storage material maintains phase stability even after exposure to 1,100°C for 6 hours. No signs of the presence of an alumina phase were observed in the oxygen storage material after aging at 1,100°C or 1,200°C. However, the formation of shoulders at peaks located at 29° and 49° 2θ angles after aging at 1,200°C for 6 hours indicates the initiation of cesium-zirconium phase segregation in the oxygen storage material.

[0057] The TPR-H2 profile of this oxygen storage material was measured and found to represent more than 85% of the usable theoretical oxygen storage capacity (OSC). The specific surface area (SSA) and pore volume (PV) of the oxygen storage material after firing were similarly measured after aging at predetermined temperatures. A summary of these results is shown in Table 2.

[0058] [Table 2]

[0059] This embodiment further demonstrates that an oxygen storage material formed according to the teachings of this disclosure remains thermally stable after aging at 1,100°C without undergoing either phase segregation or disproportionation. Furthermore, the inclusion of yttrium oxide in this composition further improves the thermal stability of the oxygen storage material, with phase segregation only beginning to be observed after aging at 1,200°C for 6 hours.

[0060] Example 3 A thermally stable oxygen storage material is prepared according to the following procedure. The composition of this oxygen storage material is 30% Al2O3, 29% CeO2, 33.5% ZrO2, 5% La2O3, and 2.5% Y2O3, with a CeO2 / ZrO2 molar ratio of 0.62.

[0061] A zirconium-containing solution is prepared by dissolving 45.1 grams of ZrOCl2·8H2O crystals in 380 grams of deionized (DI) water. 28.9 grams of 15% NaOH solution are added to the zirconium-containing solution and mixed until a clear solution of polymerized zirconium precursor is formed. Next, 15.0 grams of alumina slurry consisting of boehmite and Keggin-type aluminum nanoclusters (ratio 3:1) is added to the zirconium-containing solution. In the next step, 57.4 grams of 16.7% Na2SO4 solution are added to the zirconium-containing solution to form a zirconium-alumina precursor. 157 grams of 9.2% Ce(NO3)3 solution, 16.1 grams of 15.5% La(NO3)3 solution, and 6.3 grams of 19.75% Y(NO3)3 solution are added to the zirconium-alumina precursor and mixed thoroughly to form a slurry. Finally, slowly add the 25% NaOH solution to the slurry until the pH reaches 13. Age the slurry while maintaining the pH above 10 until a precipitate forms. Filter the formed precipitate using a Buchner funnel and wash with deionized (DI) water to remove excess cations, anions, or both. Dry the resulting precipitate, e.g., wet cake, in an electric oven at 130°C, then bake at 700°C for 2 hours.

[0062] The calcined oxygen storage powder was aged for an additional 6 hours at temperatures of 1,000°C, 1,100°C, and 1,200°C. No signs of the presence of an alumina phase or disproportionation were observed in the oxygen storage material after aging at any of the above predetermined temperatures. The X-ray diffraction (XRD) spectra measured for the oxygen storage material after aging at 1,100°C for 6 hours and 1,200°C for 6 hours are shown in Figures 4A and 4B. These spectra in Figures 4A and 4B indicate that the oxygen storage material maintains phase stability even after exposure to such thermal aging conditions.

[0063] The TPR-H2 profile of this oxygen storage material was measured and found to represent more than 85% of the theoretical oxygen storage capacity (OSC) available to the material. The specific surface area (SSA) and pore volume (PV) of the oxygen storage material after firing were similarly measured after aging at predetermined temperatures. A summary of these results is shown in Table 3.

[0064] [Table 3]

[0065] This embodiment demonstrates that an oxygen storage material formed according to the teachings of this disclosure remains thermally stable after aging at 1,100°C without undergoing either phase segregation or disproportionation. Furthermore, the inclusion of yttrium oxide in this composition further improves the thermal stability of the oxygen storage material, as it does not undergo either phase segregation or disproportionation even after aging at 1,200°C for at least 6 hours.

[0066] Example 4 A thermally stable oxygen storage material is prepared according to the following procedure. The composition of this oxygen storage material is 30% Al2O3, 29% CeO2, 33.5% ZrO2, 5% La2O3, 2.5% Pr6O 11 Therefore, the molar ratio of CeO2 / ZrO2 is 0.62.

[0067] A zirconium-containing solution is prepared by dissolving 45.1 grams of ZrOCl2·8H2O crystals in 380 grams of deionized (DI) water. 28.9 grams of 15% NaOH solution are added to the zirconium-containing solution and mixed until a clear solution of polymerized zirconium precursor is formed. Next, 15 grams of alumina slurry consisting of boehmite and Keggin-type aluminum nanoclusters (ratio 3:1) is added to the zirconium-containing solution. Next, 57.4 grams of 16.7% Na2SO4 solution are added to the slurry to form a zirconium-alumina precursor. Then, 157 grams of 9.2% Ce(NO3)3 solution, 16.1 grams of 15.5% La(NO3)3 solution, and 6.1 grams of 20.56% Pr(NO3)3 solution are added to the zirconium-alumina precursor and mixed thoroughly. Finally, 25% NaOH solution is slowly added to the slurry until the pH reaches 13. The slurry is aged while maintaining a pH above 10 until a precipitate forms. The formed precipitate is filtered using a Buchner funnel and washed with deionized (DI) water to remove excess cations, anions, or both. The resulting precipitate, such as a wet cake, is dried in an electric oven at 130°C and then baked at 700°C for 2 hours.

[0068] The calcined oxygen storage powder was aged for an additional 6 hours at temperatures of 1,000°C, 1,100°C, and 1,200°C. After 6 hours of aging at 1,000°C, no signs of the presence of an alumina phase or disproportionation were observed in the oxygen storage material. The X-ray diffraction (XRD) spectra measured for the oxygen storage material after 6 hours of aging at 1,100°C and 1,200°C are shown in Figures 5A and 5B. The X-ray diffraction spectrum shown in Figure 5A indicates that the oxygen storage material maintains phase stability even after 6 hours of exposure at 1,100°C. After 6 hours of aging at 1,100°C, no signs of the presence of other alumina phases were observed in the oxygen storage material. However, the X-ray diffraction spectrum shown in Figure 5B indicates that cesium-zirconium phase segregation has begun to occur in the oxygen storage material after 6 hours of exposure at 1,200°C.

[0069] The TPR-H2 profile of this oxygen storage material was measured and found to represent more than 85% of the usable theoretical oxygen storage capacity (OSC). The specific surface area (SSA) and pore volume (PV) of the oxygen storage material after firing were similarly measured after aging at predetermined temperatures. A summary of these results is shown in Table 4.

[0070] [Table 4]

[0071] This embodiment demonstrates that an oxygen storage material formed according to the teachings of this disclosure remains thermally stable after aging at 1,100°C without undergoing either phase segregation or disproportionation. Furthermore, it shows that the absence of yttrium oxide in this composition leads to phase segregation and disproportionation after aging at 1,200°C for 6 hours, indicating a lack of thermal stability in the oxygen storage material during such aging.

[0072] Comparative Example 1 For comparison, a reference oxygen storage material is prepared according to the following procedure. The composition of this oxygen storage material is 30% Al2O3, 22% CeO2, 40% ZrO2, 5% La2O3, and 3% Nd2O3, with a CeO2 / ZrO2 molar ratio of 0.39.

[0073] A zirconium-containing solution is prepared by dissolving 47.6 grams of basic zirconium carbonate (equivalent to 40 wt% ZrO2) in nitric acid until a clear solution of polymerized zirconium precursor is formed. Next, 15 grams of alumina slurry consisting of boehmite and Keggin-type aluminum nanoclusters (ratio 4:1) is added to the zirconium-containing solution. Then, 57.4 grams of 16.7% Na2SO4 solution is added to the zirconium-containing solution to form a zirconium-alumina precursor. Next, 65.0 grams of 16.9% Ce(NO3)3 solution, 9.6 grams of 26.1% La(NO3)3 solution, and 5.1 grams of 29.5% Nd(NO3)3 solution are added to the zirconium-alumina precursor and mixed thoroughly to form a slurry. Finally, 25% NaOH solution is slowly added to the slurry until the pH reaches 13. The slurry is aged while maintaining a pH above 10 until a precipitate forms. The formed precipitate is filtered using a Buchner funnel and washed with deionized (DI) water to remove excess cations, anions, or both. The resulting precipitate, such as a wet cake, is dried in an electric oven at 130°C and then baked at 700°C for 2 hours.

[0074] The calcined oxygen storage powder was aged for an additional 6 hours at temperatures of 1,000°C, 1,100°C, and 1,200°C. Even after 6 hours of aging at 1,000°C, no signs of the presence of an alumina phase or disproportionation were observed in the oxygen storage material. The X-ray diffraction (XRD) spectra measured for the oxygen storage material after 6 hours of aging at 1,100°C and 1,200°C are shown in Figures 6A and 6B. In Figure 6A, the X-ray diffraction spectrum shows signs of cesium-zirconium phase segregation in the oxygen storage material. As shown in Figure 6B, after 6 hours of aging at 1,200°C, the degree of phase separation in the oxygen storage material becomes even more pronounced.

[0075] Table 5 summarizes the specific surface area (SSA) and pore volume (PV) of the oxygen storage material after firing, following aging at each specified temperature.

[0076] [Table 5]

[0077] This example demonstrates that a reference oxygen storage material, representative of conventional oxygen storage materials, is not thermally stable, as it exhibited phase segregation and disproportionation after aging at 1,100°C.

[0078] While embodiments have been described in this specification in a manner that enables the writing of a clear and concise description, it is intended and will be understood that various combinations and divisions of embodiments will not depart from the present invention. For example, it will be understood that all preferred features described herein are applicable to all embodiments of the present invention described herein.

[0079] The above description of various forms of the present invention is provided for illustrative and explanatory purposes only. The above description is not intended to be exhaustive or to limit the present invention to the exact forms disclosed. Numerous modifications or alterations are possible in light of the above teachings. The forms discussed and described are selected and described in order to best illustrate the principles of the present invention and its practical applications. This allows those skilled in the art to best utilize the present invention with various modifications in various forms suitable for a particular intended use. All such modifications and alterations fall within the scope of the present invention as determined by the appended claims, provided they are interpreted in accordance with the properly, lawfully, and fairly entitled scope.

Claims

1. Oxygen storage material (OSM), Zirconium oxide and, Aluminum oxide and Cerium oxide and, An oxide of at least one rare earth metal other than cerium and Includes, The oxygen storage material remains thermally stable after aging at 1,100°C for at least 6 hours, without undergoing either phase segregation or disproportionation. Oxygen storage material.

2. An oxygen storage material according to claim 1, The oxygen storage material CeO ２ / ZrO ２ The molar ratio is, If the at least one rare earth metal includes yttrium, the range is 0.20 to 1.50, or If yttrium is absent, the value is in the range of 0.40 to 1.

50. Oxygen storage material.

3. An oxygen storage material according to claim 1 or 2, The aforementioned oxygen storage material is aluminum oxide (Al ２ O ３ The content is 40% by weight or less relative to the total mass of the oxygen storage material. Oxygen storage material.

4. An oxygen storage material according to any one of claims 1 to 3, The oxygen storage material is yttrium oxide (Y ２ O ３ The content is at least 0.5% by weight relative to the total mass of the oxygen storage material. Oxygen storage material.

5. An oxygen storage material according to any one of claims 1 to 4, CEO ２ The other at least one rare earth metal oxide is present in an amount up to 10% by weight relative to the total mass of the oxygen storage material. Oxygen storage material.

6. An oxygen storage material according to any one of claims 1 to 5, The CeO of the oxygen storage material ２ / ZrO ２ The molar ratio is If the at least one rare earth metal includes yttrium, the range is 0.35 to 1.0, or If yttrium is absent, the value is in the range of 0.40 to 1.

0. Oxygen storage material.

7. An oxygen storage material according to any one of claims 1 to 6, The oxygen storage material was aged at 1,000°C for 6 hours, and then 50 m ２ Having a specific surface area of ​​1 / g or more, Oxygen storage material.

8. An oxygen storage material according to any one of claims 1 to 6, The oxygen storage material was aged at 1,100°C for 6 hours, and then 25m ２ Having a specific surface area of ​​1 / g or more, Oxygen storage material.

9. An oxygen storage material according to any one of claims 1 to 8, If the at least one rare earth metal includes yttrium, the oxygen storage material remains thermally stable after aging in air at 1,200°C without undergoing either phase segregation or disproportionation. Oxygen storage material.

10. An oxygen storage material according to any one of claims 1 to 9, The oxygen storage capacity (OSC) of the oxygen storage material is 85% or more of the theoretical oxygen storage capacity. Oxygen storage material.

11. A method for producing a thermally stable oxygen storage material (OSM), wherein the method is: (a) A step of preparing an acidic solution containing polymerized zirconium oligomer, (b) The step of mixing the acidic solution containing the polymerized zirconium oligomer with an alumina source to form a mixture, (c) The step of mixing a complexing agent into the mixture, (d) The step of leaving the mixture to stand to form a zirconium-aluminum precursor, (e) Adding a base to the zirconium-aluminum precursor to neutralize the zirconium-aluminum precursor and form a zirconium-aluminum hydrated oxide slurry, (f) The step of mixing the zirconium-aluminum-based hydrated oxide slurry with an acidic solution containing cerium and at least one rare earth metal other than cerium to form a polyvalent metal-containing slurry, (g) A step of aging the polyvalent metal-containing slurry at a pH higher than 10 in order to enable the formation of a mixed hydrated oxide precipitate, (h) Washing the mixed hydrated oxide precipitate to remove the anionic mixture or the cationic mixture or both, (i) A step of drying the washed mixed hydrated oxide precipitate, (j) The step of calcining the dried mixed hydrated oxide precipitate to form the oxygen storage material (OSM) Includes, The oxygen storage material is thermally stable after aging at 1,100°C for at least 6 hours, without undergoing either phase segregation or disproportionation. method.

12. The method according to claim 11, The at least one rare earth metal other than cerium includes yttrium. method.

13. A method according to any one of claims 11 or 12, The polymerized zirconium oligomer contains a zirconium octamer in an amount of 30% to 100% by mass relative to the mass of the polymerized zirconium oligomer. method.

14. A method according to any one of claims 11 to 13, The polymerized zirconium oligomer contains no zirconia sol particles at all. method.

15. A method according to any one of claims 11 to 14, The aluminum source comprises one or more selected from the group consisting of dispersible aluminum hydroxide, dispersible boehmite, aluminum oxide, aluminum Keggin-type ion nanoclusters, and combinations thereof. method.

16. A method according to any one of claims 11 and 15, The amount of the aluminum Keggin-type ion nanoclusters is 25% by weight or more relative to the total aluminum content of the aluminum source. method.

17. A method according to any one of claims 11 to 16, The complexing agent is selected from the group consisting of sulfates, persulfates, oxalates, succinates, and combinations thereof. method.

18. A method according to any one of claims 11 to 17, The amount of the complexing agent added to the zirconium-aluminum acid mixture is in the range of 0.4 to 1.2 moles per mole of zirconium. method.

19. A method according to any one of claims 11 to 18, The acidic solution containing the polymerized zirconium oligomer and the acidic solution containing cerium and at least one rare earth metal other than cerium are formed using water-soluble compounds of zirconium, cerium, and at least one rare earth metal other than cerium, in the form of nitrates, chlorides, sulfates, acetates, or combinations thereof. method.

20. A method according to any one of claims 11 to 19, The base is an alkali metal hydroxide, aqueous ammonia, or both. method.

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