Surface modification of mixed oxides for high PGM dispersion

Abstract

The compositions disclosed herein are compositions having a mixed oxide core consisting of alumina-free cerium oxide and zirconium oxide. The mixed oxide core contains, based on its total weight, about 15% to about 60% by weight of cerium oxide and about 40% to about 85% by weight of zirconium oxide. The mixed oxide core has a rare earth oxide coating on its surface, the rare earth oxide being selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof. Furthermore, noble metals such as palladium or rhodium are dispersed on the surface of these compositions, and the dispersion of rhodium or palladium is higher compared to compositions containing a mixed oxide core without a rare earth oxide coating. Furthermore, methods for producing these compositions are also disclosed herein. These compositions can be used as part of a catalyst system.

Description

[Technical Field]

[0001] Cross-reference of related applications This application is filed on 8 April 2024 as an international application under the PCT (as 7 April 2024 falls on a Sunday), claiming priority and benefits of U.S. Provisional Patent Application No. 63 / 494,907 filed on 7 April 2023, the entire disclosure of which is incorporated herein by reference.

[0002] Field of Invention This application relates to a composition comprising a mixed oxide core consisting of cerium oxide and zirconium oxide, and optionally additional rare earth oxides. The mixed oxide core has a rare earth oxide coating on its surface, the rare earth oxide in the coating being selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The composition further has rhodium or palladium on its surface and exhibits a higher degree of rhodium or palladium dispersion compared to compositions without a rare earth oxide coating on the mixed oxide core. [Background technology]

[0003] Various conventional catalysts have been used to purify exhaust gases emitted from internal combustion engines and the like. These conventional catalysts are often known as three-way catalysts (TWC catalysts), and they oxidize pollutants in exhaust gases, including hydrocarbons and carbon monoxide, and reduce nitrogen oxides to relatively harmless elements of water, nitrogen, and carbon dioxide. These catalysts are used under high-temperature conditions. Therefore, these catalysts need to have high heat resistance so that they can maintain high catalytic activity even after prolonged use at high temperatures.

[0004] These TWC catalysts generally contain alumina and rare earth oxides along with precious metals (Pd, Pt, or Rh) and are coated onto a flow-through monolith. However, when exposed to high temperatures under operating conditions, sintering of the precious metal (PGM) particles occurs, leading to deactivation of the TWC catalyst. High PGM dispersion after thermal aging is required, as high PGM dispersion indicates suppressed sintering of PGM particles, because suppressed sintering preserves the active sites of the PGM, providing high catalytic performance.

[0005] To date, attempts to create catalyst compositions that maintain their effectiveness even under high-temperature conditions over extended periods have not been entirely successful. Therefore, there is still a need to develop mixed oxides that can be used as catalysts exhibiting high PGM dispersion even after thermal aging. [Overview of the Initiative]

[0006] The mixed oxide compositions disclosed herein include cerium oxide and zirconium oxide having a rare earth oxide coating. Mixed oxide cores having a rare earth oxide coating are also described herein as mixed oxides surface-modified with rare earth oxides. These compositions have noble metals on their surface and do not contain alumina. The compositions disclosed herein are generally mixed oxide compositions. These compositions have a high degree of noble metal dispersion. The compositions may be suitable for catalytic applications as part of a catalytic system and may be used for exhaust gas purification.

[0007] The compositions disclosed herein include a mixed oxide core, which comprises about 15% to about 60% by weight of cerium oxide and about 40% to about 85% by weight of zirconium oxide based on the total weight of the mixed oxide core, and neither the mixed oxide core nor the overall composition contains alumina. The mixed oxide core has a rare earth oxide coating on its surface, and the rare earth oxide is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The compositions of a mixed oxide core having a rare earth oxide coating have rhodium or palladium on their surface. These compositions disclosed herein exhibit a higher degree of rhodium or palladium dispersion compared to compositions having a mixed oxide core without a rare earth oxide coating or without a rare earth oxide coating.

[0008] In certain embodiments, it is desirable that the cerium component in the overall composition be at least approximately 40% by weight in order to obtain a high degree of palladium dispersion. In other embodiments, it is desirable that the cerium component in the overall composition be at most approximately 25% by weight in order to obtain a high degree of rhodium dispersion.

[0009] In some embodiments, the composition has rhodium dispersed on the surface, with a rhodium dispersion of approximately 18.5% to approximately 28.6% after firing (i.e., aging) in air at 800°C for 2 hours, or approximately 14.3% to approximately 21.9% after additional firing (i.e., aging) in air at 1000°C for 10 hours, or approximately 10.3% to approximately 16.5% after further additional firing (i.e., aging) in air at 1100°C for 10 hours.

[0010] In other embodiments, the composition has palladium dispersed on its surface, with a palladium dispersion of approximately 35.0% to approximately 46.1% after firing (i.e., aging) in air at 800°C for 2 hours, or approximately 8.5% to approximately 13.0% after firing (i.e., aging) in air at 1000°C for 10 hours, or approximately 3.9% to approximately 6.0% after firing (i.e., aging) in air at 1100°C for 10 hours.

[0011] In certain embodiments, the composition comprises a mixed oxide core substantially composed of additional rare earth oxides selected from the group consisting of cerium oxide, zirconium oxide and lanthanum oxide, neodymium oxide, praseodymium oxide, yttrium oxide and mixtures thereof. The rare earth oxide coating is one or two of cerium oxide, neodymium oxide and praseodymium oxide. The composition has rhodium or palladium on its surface. In the case of palladium, the palladium dispersion is approximately 35.0% to approximately 46.1% after firing in air at 800°C for 2 hours, or approximately 8.5% to approximately 13.0% after firing in air at 1000°C for 10 hours, or approximately 3.9% to approximately 6.0% after firing in air at 1100°C for 10 hours. In the case of rhodium, the rhodium dispersion is approximately 18.5% to 28.6% after firing in air at 800°C for 2 hours, or approximately 14.3% to 21.9% after firing in air at 1000°C for 10 hours, or approximately 10.3% to 16.5% after firing in air at 1100°C for 10 hours.

[0012] This disclosure also discloses a method for producing a composition having a rhodium or palladium coating on its surface, comprising a mixed oxide core having a rare earth oxide coating on its surface. The method comprises the following steps: (a) providing a mixed oxide powder of cerium oxide, zirconium oxide, and optionally one or more rare earth oxides selected from the group consisting of neodymium, lanthanum, praseodymium, and yttrium; (b) preparing a rare earth solution by dissolving a rare earth salt containing a rare earth element selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof in water; (c) mixing the rare earth solution with the mixed oxide powder to obtain a homogeneous powder mixture; and (d) firing the homogeneous powder mixture at approximately 400°C to 600°C, preferably 500°C, for approximately 2 to 5 hours, preferably 3 hours, to obtain a rare earth oxide coating on its surface. A step of obtaining a mixed oxide core, wherein the rare earth oxide for the coating is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof; (e) adding a rhodium or palladium salt solution to the mixed oxide core having the rare earth oxide coating; and (f) firing at about 500°C to about 650°C, preferably 550°C, for about 2 hours to about 5 hours, preferably 2 hours to obtain an oxide composition containing a mixed oxide core having a rare earth oxide coating and having a higher degree of rhodium or palladium dispersion compared to a composition having a mixed oxide core without a rare earth oxide coating.

[0013] In one embodiment, the firing in step (d), the "first firing," is carried out at approximately 500°C for about 3 hours. In one embodiment, the firing in step (f), the "second firing," is carried out at approximately 550°C for about 2 hours. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 (FIG.1) shows a flowchart illustrating one embodiment of a method for producing the composition described herein. [Modes for carrying out the invention]

[0015] This disclosure generally relates to compositions of mixed oxide cores comprising cerium oxide, zirconium oxide, and optionally additional rare earth oxides. The mixed oxide cores and the overall compositions do not contain alumina. The mixed oxide cores have a rare earth oxide coating on their surface, and the rare earth oxides are selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. These compositions are generally mixed oxide compositions having a high degree of noble metal dispersion, particularly a high degree of rhodium or palladium dispersion. Mixed oxide cores having a rare earth oxide coating are also described in this disclosure as surface-modified mixed oxides, where the surface modification is an additional rare earth oxide coating.

[0016] Compositions of mixed oxide cores having a rare earth oxide coating have a noble metal on their surface, and in some embodiments, this noble metal is rhodium or palladium. These compositions disclosed herein have a higher degree of noble metal dispersion compared to compositions containing mixed oxide cores without a rare earth oxide coating. In certain embodiments, the compositions disclosed herein have a higher degree of rhodium or palladium dispersion compared to compositions containing mixed oxide cores without a rare earth oxide coating. In this comparison, the mixed oxide cores are compositionally identical except for the rare earth oxide coating.

[0017] Before disclosing and describing compositions comprising zirconium oxide and cerium oxide but not alumina, and methods for producing the same, it should be understood that this disclosure is not limited to the specific structures, steps, or materials disclosed herein, but also extends to equivalents recognized by those skilled in the art. Furthermore, it should be understood that the terms used herein are for the purpose of describing specific embodiments only and are not to be constrained. In this specification, the singular forms "a," "an," and "the" also include plural subjects unless the context clearly indicates otherwise. Thus, for example, a reference to "a step" may include multiple steps; a reference to "producing / products" does not mean all products obtained by the reaction or treatment; and a reference to "treating" may include one or more such treatment steps. Therefore, a "treatment step" may include treating similar materials or substances / fluids multiple or repeatedly to obtain a particular treatment product.

[0018] Numerical values ​​accompanied by “about” or “approximately” include normal experimental error, and these terms “about” and “approximately” are used interchangeably. In this disclosure, “about” or “approximately” means within a statistically significant range for a value such as particle size, concentration range, time range, molecular weight, temperature, or pH. This range includes variation of roughly one order of magnitude, usually within 10%, and more generally within 5% of the indicated value or range. In some cases, this range may be within the normal experimental error range of the standard method used to measure and / or determine the given value or range. The range of tolerance for “about” varies depending on the system under consideration and will be readily understood by those skilled in the art. Wherever a range is described in this application, all integer values ​​within that range are also included as an aspect of the invention.

[0019] "Based on the total weight of the composition" and "based on the overall composition" are used interchangeably and are distinguished from "based on the total weight of the mixed oxide core". The expression "surface modification with rare earth oxide" is also used interchangeably with "rare earth oxide coating" in this disclosure.

[0020] This application relates to oxide compositions. These compositions have a mixed oxide core, and the mixed oxide core has a rare earth coating on its surface. The mixed oxide core contains from about 15 wt% to about 60 wt% cerium oxide and from about 40 wt% to about 85 wt% zirconium oxide, based on the total weight of the mixed oxide core, and does not contain alumina. In fact, the overall compositions in this disclosure do not contain alumina.

[0021] "Does not contain alumina" means that the composition contains from less than about 0.1 wt% to about 0 wt% alumina. In some embodiments, "does not contain alumina" means that it does not contain a detectable amount of alumina or contains about 0 wt% alumina. In all embodiments of the compositions in this disclosure, both the mixed oxide core and the overall composition do not contain alumina in accordance with the above definition.

[0022] In addition to zirconium oxide and cerium oxide, the mixed oxide core may also optionally contain one or more rare earth oxides other than cerium. These additional and optional rare earth oxides include oxides of any rare earth element other than cerium. In certain embodiments, the one or more rare earth oxides added to the mixed oxide core are lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide. Thus, the mixed oxide core may also optionally contain one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide. Thus, the compositions according to this disclosure contain zirconium oxide and cerium oxide and further contain a mixed oxide core that optionally contains additional rare earth oxides selected from the group consisting of yttrium oxide, lanthanum oxide, neodymium oxide, praseodymium oxide, and mixtures thereof.

[0023] In certain embodiments, the mixed oxide core comprises two of these additional oxides. In other embodiments, the mixed oxide core comprises three of these additional oxides. In certain embodiments, the composition comprises a mixed oxide core essentially composed of additional rare earth oxides selected from the group consisting of cerium oxide, zirconium oxide and lanthanum oxide, neodymium oxide, praseodymium oxide, yttrium oxide and mixtures thereof.

[0024] As described above, the mixed oxide core has a rare earth oxide coating on its surface. This can also be expressed as a mixed oxide surface-modified with a rare earth oxide. The rare earth elements of the rare earth oxide coating are selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. In certain embodiments, the rare earth oxide coating on the surface is one or two of cerium oxide, neodymium oxide, and praseodymium oxide. The rare earth oxide coating may be present in an amount of about 1% to about 10% by weight based on the total weight of the composition. In certain embodiments, the rare earth oxide coating may be present in an amount of about 1% to about 8% by weight based on the total weight of the composition. In even more certain embodiments, the rare earth oxide coating may be present in an amount of about 1% to about 6% by weight based on the total weight of the composition.

[0025] The mixed oxide core contains about 15% to about 60% by weight of cerium oxide and about 40% to about 85% by weight of zirconium oxide, based on the total weight of the mixed oxide core, and does not contain alumina. The overall composition contains about 15% to about 60% by weight of cerium oxide and about 40% to about 85% by weight of zirconium oxide, based on the total weight of the composition, and the overall composition does not contain alumina.

[0026] In embodiments in which the mixed oxide core contains additional rare earth oxides, one or more additional rare earth oxides may be present in an amount of about 2% to about 15% by weight based on the total weight of the composition. In certain embodiments, one or more additional rare earth oxides may be present in an amount of about 5% to about 12% by weight based on the total weight of the composition. In certain embodiments, one or more additional rare earth oxides may be present in an amount of about 7% to about 10% by weight based on the total weight of the composition.

[0027] In a particular embodiment, the composition comprises CeO2 and ZrO2, and La2O3, Y2O3, Nd2O3 and Pr6O 11 The mixed oxide core has one or more of the following, and the mixed oxide core has a rare earth oxide coating on its surface, and the rare earth elements of the rare earth oxide coating are CeO2, Nd2O3 and Pr6O 11 It is one or two of these. In certain embodiments of these compositions, the composition has rhodium on its surface, and in other embodiments, the composition has palladium on its surface.

[0028] In the compositions of this disclosure, the rare earth coating is present in an amount of about 1% to about 10% by weight based on the total weight of the composition. In certain embodiments, the rare earth oxide coating is a single rare earth oxide, the rare earth element of which is selected from the group consisting of cerium, lanthanum, neodymium, and praseodymium, and the rare earth oxide coating is present in an amount of about 1% to about 5% by weight based on the total weight of the composition. In other embodiments, the rare earth oxide coating consists of two types of rare earth oxides, the rare earth elements of each of these two rare earth oxide coatings are independently selected from the group consisting of cerium, lanthanum, neodymium, and praseodymium, and each coated rare earth oxide is present in an amount of about 1% to about 5% by weight based on the total weight of the composition (therefore, the total rare earth oxide coating is present in an amount of about 2% to about 10% by weight based on the total weight of the composition).

[0029] The composition further has noble metals on its surface. These noble metals may be any platinum group metals, including platinum, palladium, and rhodium. In certain embodiments, the composition has palladium or rhodium dispersed on its surface. As disclosed and described herein, this composition has a higher degree of platinum group metal dispersion than a composition having a mixed oxide core without (i.e., without) a rare earth oxide coating. In certain embodiments, the composition has a higher degree of rhodium or palladium dispersion than a composition having a mixed oxide core without (i.e., without) a rare earth oxide coating. This combination of a mixed oxide core and a rare earth oxide coating yields an improved composition having a higher degree of noble metal dispersion, and in certain embodiments, a higher degree of rhodium or palladium dispersion. Therefore, the oxide compositions according to this disclosure are more suitable for use as catalysts or catalytic compositions.

[0030] In certain embodiments, the noble metal is palladium, and in other embodiments, the noble metal is rhodium. The noble metal may be present on the surface in a metallic or oxide state. In certain embodiments, the composition contains rhodium, which is present as an oxide, comprising about 0.3% by weight of Rh2O3 to about 0.8% by weight of Rh2O3 based on the whole composition, and in certain embodiments, comprising about 0.5% by weight of Rh2O3 based on the whole composition. In other embodiments, the composition contains palladium, which is present as an oxide, comprising about 1.0% by weight of PdO to about 2.0% by weight of PdO based on the whole composition, and in a particularly preferred embodiment, comprising about 1.6% by weight of PdO based on the whole composition.

[0031] To obtain a high degree of palladium dispersion, it is desirable that the proportion of cerium in the overall composition be at least about 40% by weight. To obtain a high degree of rhodium dispersion, it is desirable that the proportion of cerium in the overall composition be at most about 25% by weight.

[0032] In certain embodiments containing palladium, the composition comprises a mixed oxide core comprising about 35% to about 60% by weight of cerium oxide, about 40% to about 65% by weight of zirconium oxide, and one or more lanthanum oxides, neodymium oxides, praseodymium oxides, and yttrium oxides, based on the weight of the mixed oxide core. The mixed oxide core has a rare earth oxide coating, the rare earth element of the rare earth oxide coating being selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. In certain embodiments of these embodiments, the mixed oxide core further comprises lanthanum oxide, neodymium oxide, and praseodymium oxide. In other embodiments of these embodiments, the mixed oxide core further comprises lanthanum oxide, neodymium oxide, and yttrium oxide. In certain embodiments of these embodiments, the rare earth oxide coating is neodymium oxide, cerium oxide, praseodymium oxide, or a mixture thereof. This composition has a higher degree of palladium dispersion compared to compositions having a mixed oxide core with or without a rare earth oxide coating. In this comparison, the mixed oxide cores are compositionally identical except for the presence or absence of the rare earth oxide coating.

[0033] In embodiments comprising other palladium, the composition comprises a mixed oxide core, which comprises about 35% to about 60% by weight of cerium oxide and about 40% to about 65% by weight of zirconium oxide, based on the total weight of the mixed oxide core, and optionally one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, but does not contain alumina. The mixed oxide core has a rare earth oxide coating, the rare earth elements of the rare earth oxide coating are selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The composition has palladium dispersed on its surface, with a palladium dispersion of about 35.0% to about 46.1% after firing in air at 800°C for 2 hours, about 8.5% to about 13.0% after firing in air at 1000°C for 10 hours, or about 3.9% to about 6.0% after firing in air at 1100°C for 10 hours.

[0034] In embodiments containing specific rhodium, the composition comprises a mixed oxide core, which comprises about 15% to about 25% by weight of cerium oxide, about 70% to about 85% by weight of zirconium oxide and one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, based on the weight of the mixed oxide core. The mixed oxide core has a rare earth oxide coating, where the rare earth element of the rare earth oxide coating is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. In certain embodiments of these embodiments, the mixed oxide core further comprises lanthanum oxide and neodymium oxide. In certain embodiments of these embodiments, the rare earth oxide coating is neodymium oxide, cerium oxide, or a mixture thereof. The composition has a higher degree of rhodium dispersion compared to compositions having a mixed oxide core without or without a rare earth oxide coating. In this comparison, the mixed oxide core is compositionally identical except for the presence or absence of the rare earth oxide coating.

[0035] In embodiments comprising other rhodium, the composition comprises a mixed oxide core, which comprises about 15% to about 25% by weight of cerium oxide and about 70% to about 85% by weight of zirconium oxide, based on the total weight of the mixed oxide core, and optionally one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, but does not contain alumina. The mixed oxide core has a rare earth oxide coating, the rare earth elements of the rare earth oxide coating are selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The composition has rhodium dispersed on its surface, with a rhodium dispersion of about 18.5% to about 28.6% after firing in air at 800°C for 2 hours, about 14.3% to about 21.9% after firing in air at 1000°C for 10 hours, or about 10.3% to about 16.5% after firing in air at 1100°C for 10 hours.

[0036] The compositions relating to this disclosure may contain trace amounts of impurities. These impurities are typically present in amounts of about 1% by weight or less (up to about 0 or undetectable) based on the total weight of the composition. These impurities include residual solvents, salts, and other metals. These other metals include magnesium, iron, calcium, silicon, and sodium, which are commonly found in water. The amount of these impurities (from about 1% by weight to about 0 or undetectable) may be present in any of the embodiments of the compositions described in this disclosure. If present and detectable, each impurity may be present in amounts of about 100 ppm or less.

[0037] Measurement of rhodium dispersion The rhodium dispersion was determined from the amount of CO adsorbed, measured using the CO pulse chemisorption method. Characterization was performed on aged powder samples using the Micrometrics Autochem 2920 system. Approximately 0.5 g of rhodium-supported sample was weighed into a quartz sample tube packed with quartz wool, and a flow rate of 50 cm³ was applied. 3 The solution was reduced at 900°C for 30 minutes under a 10% H2 / Ar solution. Subsequently, a 50cm solution was used. 3 He was circulated for 30 minutes. After that, 50cm 3 The sample was cooled to 35°C under a flow of He per minute. 10% CO / He was pulsed into the sample every 2 minutes until adsorption reached saturation. The stoichiometric ratio of CO to rhodium atoms was assumed to be 1:1. The sample mass after analysis was used to quantify the degree of rhodium dispersion.

[0038] In certain embodiments, the composition comprises a mixed oxide core that does not contain alumina, comprising about 15% to about 25% by weight of cerium oxide, about 70% to about 85% by weight of zirconium oxide and one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide. The mixed oxide core has a rare earth coating. The rare earth element of the rare earth oxide coating is selected from neodymium, cerium, praseodymium, or a mixture thereof. The composition does not contain alumina and has a higher degree of rhodium dispersion compared to compositions having a mixed oxide core without or without a rare earth oxide coating.

[0039] In certain embodiments, the composition comprises a mixed oxide core substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, and neodymium oxide, with the rare earth coating being either or both cerium oxide and neodymium oxide. The composition is alumina-free and has a higher degree of rhodium dispersion compared to compositions having a mixed oxide core with or without a rare earth oxide coating.

[0040] In additional embodiments in which rhodium is present on the surface of the composition, the composition comprises about 20% to about 25% by weight of cerium oxide and about 1% to about 10% by weight of a rare earth oxide coating based on the total weight of the composition.

[0041] In certain embodiments, the composition comprises a mixed oxide core, the mixed oxide core comprising about 15% to about 25% by weight of cerium oxide, about 70% to about 85% by weight of zirconium oxide based on the total weight of the mixed oxide core, and optionally one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, but without alumina. The mixed oxide core has a rare earth oxide coating, the rare earth element of the rare earth oxide coating is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The composition further contains rhodium dispersed on its surface, with rhodium dispersion levels of approximately 18.5% to 28.6% after aging at 800°C in air for 2 hours, approximately 14.3% to 21.9% after aging at 1000°C in air for 10 hours, or approximately 10.3% to 16.5% after aging at 1100°C in air for 10 hours. These additional aging processes are performed after the preparation of the composition. These additional aging processes can be carried out independently.

[0042] In certain embodiments, the composition comprises about 20% to about 25% by weight of cerium oxide and about 1% to about 10% by weight of a rare earth oxide coating based on the total weight of the composition, with rhodium dispersed on the surface. In these embodiments, the composition has a higher degree of rhodium dispersion than compositions having a mixed oxide core without or without a rare earth oxide coating. The degree of rhodium dispersion may be about 18.5% to about 28.6% after aging at 800°C in air for 2 hours, about 14.3% to about 21.9% after aging at 1000°C in air for 10 hours, or about 10.3% to about 16.5% after aging at 1100°C in air for 10 hours. These additional aging processes are performed after the preparation of the composition. These additional aging processes may be performed independently.

[0043] In certain embodiments, the rhodium dispersion may be approximately 21% after firing (aging) at 800°C in air for 2 hours, approximately 15% after firing (aging) at 1000°C in air for 10 hours, or approximately 10.5% after firing (aging) at 1100°C in air for 10 hours.

[0044] The percentage of rhodium dispersion does not indicate the proportion of the surface that is covered with rhodium. Rather, it indicates the proportion of rhodium atoms that exist as surface atoms. For example, theoretical 100% rhodium dispersion means that all rhodium atoms (added to the composition) exist as surface rhodium atoms. This parameter is typically used to quantify the degree of sintering of rhodium particles after firing (aging).

[0045] As described in this disclosure, the aging conditions are not cumulative. The rhodium dispersion value is obtained after preparing a composition comprising a mixed oxide core having rhodium on its surface and a rare earth oxide coating. In the composition preparation process, a heat treatment or sintering is performed before the addition of rhodium, and a second sintering or heat treatment is performed after the addition of rhodium. The composition obtained by this process is referred to as a “fresh” or “as prepared” composition. The heat treatment or sintering after the addition of rhodium is performed at about 500°C to about 650°C (preferably about 550°C) for about 2 to 5 hours (preferably about 2 hours). Aging sintering to evaluate the degree of sintering of rhodium particles is performed individually under different conditions as described in this disclosure. These additional sintering or aging treatments can be performed in air at about 800°C for about 2 hours, at about 1000°C for about 10 hours, or at about 1100°C for about 10 hours, and are used to evaluate rhodium sintering under simulated use conditions.

[0046] Measurement of palladium dispersion Palladium dispersion was determined from the amount of CO adsorbed, measured using the CO pulsed chemisorption method. Characterization was performed on aged powder samples using the Micrometrics Autochem 2920 system. Approximately 0.5 g of palladium-supported sample was weighed into a quartz sample tube packed with quartz wool, and a flow rate of 50 cm³ was applied. 3 The solution was reduced at 400°C for 30 minutes under a 10% H2 / Ar solution. Subsequently, a 50cm solution was used. 3 He was circulated for 30 minutes. After that, 50cm 3 The sample was cooled to 35°C under a flow of He per minute. 10% CO / He was pulsed into the sample every 2 minutes until adsorption reached saturation. The stoichiometric ratio of CO to palladium atoms was assumed to be 1:1. The post-analysis sample mass was used to quantify the palladium dispersion rate.

[0047] In certain embodiments, the composition comprises a mixed oxide core containing about 35% to about 60% by weight of cerium oxide, about 40% to about 65% by weight of zirconium oxide and one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, but without alumina. The mixed oxide core has a rare earth coating. The rare earth element of the rare earth oxide coating is selected from neodymium, cerium, praseodymium, or a mixture thereof. The composition has a higher degree of palladium dispersion compared to compositions having a mixed oxide core without or without a rare earth oxide coating.

[0048] In certain embodiments, the composition comprises a mixed oxide core substantially composed of two or more of cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, with the rare earth coating being cerium oxide, neodymium oxide, or praseodymium oxide. The composition does not contain alumina and has a higher degree of rhodium dispersion compared to compositions having a mixed oxide core with or without a rare earth oxide coating.

[0049] In additional embodiments in which palladium is present on the surface of the composition, the composition comprises about 40% to about 60% by weight of cerium oxide and about 1% to about 10% by weight of a rare earth oxide coating based on the total weight of the composition.

[0050] In certain embodiments, the composition comprises a mixed oxide core, which comprises about 35% to about 60% by weight of cerium oxide and about 40% to about 65% by weight of zirconium oxide based on the total weight of the mixed oxide core, and optionally one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, but does not contain alumina. The mixed oxide core has a rare earth oxide coating, the rare earth elements of the rare earth oxide coating are selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The composition has palladium dispersed on its surface, with a palladium dispersion of about 35.0% to about 46.1% after firing at 800°C in air for 2 hours, about 8.5% to about 13.0% after firing at 1000°C in air for 10 hours, or about 3.9% to about 6.0% after firing at 1100°C in air for 10 hours.

[0051] In certain embodiments, the composition comprises a mixed oxide core substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide, with the rare earth coating being cerium oxide, neodymium oxide, or praseodymium oxide. The composition is alumina-free and has a higher degree of palladium dispersion compared to compositions having a mixed oxide core with or without a rare earth oxide coating.

[0052] In other specific embodiments, the composition comprises a mixed oxide core substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and yttrium oxide, with the rare earth coating being cerium oxide or neodymium oxide. The composition is alumina-free and has a higher degree of palladium dispersion compared to compositions having a mixed oxide core with or without a rare earth oxide coating.

[0053] In other specific embodiments, the composition comprises a mixed oxide core substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide, with the rare earth coating being cerium oxide or neodymium oxide. This composition does not contain alumina and has a higher degree of palladium dispersion compared to compositions having a mixed oxide core with or without a rare earth oxide coating.

[0054] In certain embodiments, the composition comprises a mixed oxide core, which, based on the total weight of the mixed oxide core, comprises about 35% to about 60% by weight of cerium oxide, about 40% to about 65% by weight of zirconium oxide, and optionally one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, but does not contain alumina. The mixed oxide core has a rare earth oxide coating, the rare earth elements of the rare earth oxide coating being selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The composition further comprises palladium dispersed on the surface, with a palladium dispersion of about 35.0% to about 46.1% after aging at 800°C in air for 2 hours, about 8.5% to about 13.0% after aging at 1000°C in air for 10 hours, or about 3.9% to about 6.0% after aging at 1100°C in air for 10 hours. These additional firings (or agings) are aging processes performed after the preparation of the composition. These additional firings (or agings) can be performed independently.

[0055] In certain embodiments, the composition comprises about 40% to about 60% by weight of cerium oxide and about 1% to about 10% by weight of a rare earth oxide coating based on the total weight of the composition, with palladium dispersed on the surface. In these embodiments, the composition has a higher degree of palladium dispersion compared to compositions having a mixed oxide core without or without a rare earth oxide coating. The degree of palladium dispersion may be about 35.0% to about 46.1% after aging at 800°C in air for 2 hours, about 8.5% to about 13.0% after aging at 1000°C in air for 10 hours, or about 3.9% to about 6.0% after aging at 1100°C in air for 10 hours. These additional aging processes are performed after the preparation of the composition. These additional aging processes may be performed independently.

[0056] In some embodiments, the palladium dispersion may be about 35.0% to about 46.1% after aging at 800°C in air for 2 hours, about 8.5% to about 12.3% after aging at 1000°C in air for 10 hours, or about 3.9% to about 5.8% after aging at 1100°C in air for 10 hours.

[0057] In certain embodiments, the palladium dispersion may be approximately 40% after aging at 800°C in air for 2 hours, approximately 10.0% after aging at 1000°C in air for 10 hours, or approximately 4% after aging at 1100°C in air for 10 hours.

[0058] The percentage of palladium dispersion does not indicate the proportion of the surface covered with palladium. Rather, it indicates the proportion of palladium atoms that exist as surface atoms. For example, theoretical 100% palladium dispersion means that all palladium atoms (added to the composition) exist as surface palladium atoms. This parameter is typically used to quantify the degree of sintering of palladium particles after firing (aging).

[0059] As described herein, the aging conditions are not cumulative. The palladium dispersion value is obtained after a mixed composition containing a mixed oxide core having a rare earth oxide coating with palladium on its surface is prepared by aging. During this preparation, the composition is heat-treated or sintered before the addition of palladium, and a second sintering or heat treatment is performed after the addition of palladium. This step yields a "fresh" or "as prepared" composition. The heat treatment or sintering performed during the preparation of the composition after the addition of palladium is carried out at about 500°C to about 650°C (preferably 550°C) for about 2 to 5 hours (preferably about 2 hours). Aging sintering to test the degree of sintering of palladium particles is carried out independently under different conditions as described herein. These additional firing or aging processes can be carried out in air at approximately 800°C for approximately 2 hours, or at approximately 1000°C for approximately 10 hours, or at approximately 1100°C for approximately 10 hours, and are used to evaluate the sintering of palladium during simulated use.

[0060] In certain embodiments, when rhodium dispersion is present, the composition comprising a mixed oxide core and a rare earth coating comprises zirconium oxide, cerium oxide, lanthanum oxide, and neodymium oxide. In these embodiments, the mixed oxide core comprises zirconium oxide, cerium oxide, lanthanum oxide, and neodymium oxide, and the rare earth elements of the rare earth oxide coating may be cerium, neodymium, or a mixture thereof. In this embodiment, the mixed oxide core of the composition has a Ce / Zr / La / Nd ratio of about 18.5% to about 21.5% by weight of cerium, about 74% to about 77% by weight of zirconium, about 1.5% to about 2.0% by weight of lanthanum, and about 2.0% to about 2.5% by weight of neodymium, in terms of oxides, and the rare earth oxide coating is substantially composed of either or both CeO2 and / or Nd2O3. In certain embodiments of these embodiments, the rare earth oxide coating is about 3% to about 6% by weight based on the total weight of the composition.

[0061] In certain embodiments having palladium dispersion, the composition comprising a mixed oxide core and a rare earth coating comprises zirconium oxide, cerium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide. In these embodiments, the mixed oxide core comprises zirconium oxide, cerium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide, and the rare earth of the rare earth oxide coating is cerium, neodymium, or praseodymium. In this embodiment, the mixed oxide core of the composition has a Ce / Zr / La / Nd / Pr ratio of about 36.5 wt% to about 41.5 wt% Ce, about 50 wt% to about 53 wt% Zr, about 2 wt% to about 2.2 wt% La, about 1 wt% to about 4.3 wt% Nd, and about 1 wt% to about 4.3 wt% Pr in terms of oxides, and the rare earth oxide coating is substantially composed of one or two of CeO2, Nd2O3, and Pr6O 11 and is substantially composed of one or two of these. In these embodiments, the rare earth oxide coating is about 1 wt% to about 6 wt% based on the total weight of the composition.

[0062] In certain embodiments having palladium dispersion, the composition comprising a mixed oxide core and a rare earth oxide coating comprises zirconium oxide, cerium oxide, lanthanum oxide, yttrium oxide, and optionally neodymium oxide. In these embodiments, the mixed oxide core may comprise zirconium oxide, cerium oxide, lanthanum oxide, yttrium oxide, and optionally neodymium oxide, and the rare earth of the rare earth oxide coating may be cerium or neodymium. In this embodiment, the mixed oxide core of the composition has a Ce / Zr / La / Nd / Y ratio of about 36.5 wt% to about 41.5 wt% Ce, about 50 wt% to about 53 wt% Zr, about 3.5 wt% to about 5.5 wt% La, about 0 wt% to about 1.5 wt% Nd, and about 1.8 wt% to about 5.6 wt% Y in terms of oxides, and the rare earth oxide coating is substantially composed of CeO2 or Nd2O3. In these embodiments, the rare earth oxide coating is about 3 wt% to about 6 wt% based on the total weight of the composition.

[0063] All compositions described above do not contain alumina. All compositions described above can be combined with the rhodium or palladium dispersion rates described above after aging.

[0064] The compositions described herein can be used as part of a catalyst system or incorporated into a catalyst composition. These catalysts can be used for exhaust gas purification. Due to their high rhodium or palladium dispersion, these compositions are particularly suitable for use as part of a catalyst system or as a catalyst support. The catalysts are used for purifying exhaust gases in automobiles and other related applications.

[0065] Furthermore, this disclosure also discloses a method for producing the compositions, which comprises a mixed oxide core having a rare earth oxide coating on its surface. These compositions having a high degree of rhodium or palladium dispersion disclosed herein are obtained by a method for providing a mixed oxide core having a rare earth oxide coating, thereby obtaining a higher degree of rhodium or palladium dispersion. Figure 1 is a flowchart showing one embodiment of a method for producing these compositions having a high degree of rhodium or palladium dispersion.

[0066] This method includes the following steps: (a) Providing a mixed oxide powder of cerium oxide, zirconium oxide, and optionally one or more rare earth oxides selected from neodymium, lanthanum, praseodymium, and yttrium; (b) Dissolving a rare earth salt in water to prepare a rare earth solution, wherein the rare earth element of the rare earth salt is selected from cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof; (c) Mixing the rare earth solution with the mixed oxide powder to obtain a homogeneous powder mixture; (d) Calcining the homogeneous powder mixture at about 400°C to about 600°C (preferably 500°C) for about 2 to 5 hours (preferably 3 hours) to obtain a mixed oxide core having a rare earth oxide coating on its surface, wherein the rare earth element of the rare earth oxide coating is selected from cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof; (e) Adding a rhodium or palladium salt solution to the mixed oxide core having the rare earth oxide coating; and (f) The process includes the step of firing at approximately 500°C to approximately 650°C (preferably 550°C) for approximately 2 to approximately 5 hours (preferably 2 hours) to obtain a composition having a rare earth oxide coating on its surface and having a higher degree of rhodium or palladium dispersion compared to a composition containing a mixed oxide core without a rare earth oxide coating. In one embodiment, the firing in step (d) ("first firing") is carried out at approximately 500°C for approximately 3 hours. In one embodiment, the firing in step (f) ("second firing") is carried out at approximately 550°C for approximately 2 hours. These two specific embodiments or steps (d) and (f) can be carried out in combination.

[0067] The mixed oxide powder comprises zirconium oxide powder and cerium oxide powder, and optionally includes one or more rare earth oxide powders from neodymium, lanthanum, praseodymium, and yttrium. The mixed oxide powder of step (a) can be divided into equal portions based on mass, as shown in the flowchart of Figure 1.

[0068] The rare earth salt in step (b) may be any water-soluble rare earth salt. These salts may be inorganic salts or organic acid salts. Examples of water-soluble salts include chlorides, sulfates, nitrates, ammonium nitrates, and acetates. In certain embodiments, the rare earth salt may be a chloride salt, a nitrate, or an ammonium nitrate salt. The rare earth salt is dissolved in water to obtain a rare earth salt solution. As described herein, the rare earth element of the salt may be cerium, lanthanum, praseodymium, neodymium, yttrium, or a mixture thereof. In certain embodiments, the rare earth element is cerium, neodymium, praseodymium, or a mixture thereof. The rare earth salt solution may have any suitable rare earth concentration in g / L units.

[0069] In certain embodiments, the rare earth salt may be cerium nitrate, cerium ammonium nitrate, neodymium nitrate, neodymium acetate, praseodymium nitrate, praseodymium acetate, or a mixture thereof.

[0070] A rare earth solution is mixed with mixed oxide powder to obtain a homogeneous mixture. A homogeneous mixture can also be obtained by dividing the mixed oxide powder into small, equal portions, adding a small amount of rare earth salt solution to each portion individually and mixing, and then mixing all the mixed oxide portions together. The rare earth salt solution forms a rare earth oxide coating on the mixed oxide core. In other words, it is also appropriate to describe the rare earth salt solution as something that modifies the surface of the mixed oxide.

[0071] A homogeneous powder mixture can be calcined at a temperature of about 400°C to about 600°C (about 500°C in some embodiments) for about 2 to 5 hours (about 3 hours in some embodiments) to obtain a mixed oxide core having a rare earth oxide coating on its surface, the rare earth elements of the rare earth oxide coating being selected from cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof. Thus, after calcination, a rare earth oxide coating is formed on the surface of the mixed oxide core, the rare earth elements being selected from cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof. Calcination can be carried out in a mixed gas of 2% oxygen and 98% nitrogen.

[0072] After firing, a precious metal is added to the mixed oxide core having a rare earth coating. In certain embodiments, rhodium or palladium is added to the mixed oxide core having a rare earth coating after firing. Generally, rhodium or palladium is added to the mixed oxide core having a rare earth oxide coating in the form of a rhodium salt or palladium salt solution. After the addition or impregnation of rhodium or palladium, the composition is fired at about 500°C to about 650°C (about 550°C in some embodiments) for about 2 hours to about 5 hours (about 2 hours in some embodiments) to obtain a composition containing a mixed oxide core having a rare earth oxide coating on its surface and having a higher degree of rhodium or palladium dispersion compared to a composition containing a mixed oxide core without a rare earth oxide coating.

[0073] In a particular embodiment, the mixed oxide powder comprises cerium oxide, zirconium oxide, neodymium oxide, and lanthanum oxide, and a rhodium salt is added in step (e). In another embodiment, the mixed oxide powder comprises cerium oxide, zirconium oxide, neodymium oxide, lanthanum oxide, and praseodymium oxide, and a palladium salt is added in step (e). In yet another embodiment, the mixed oxide powder comprises cerium oxide, zirconium oxide, neodymium oxide, lanthanum oxide, and yttrium oxide, and a palladium salt is added in step (e). In yet another embodiment, the mixed oxide powder comprises cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide, and a palladium salt is added in step (e).

[0074] In a particular embodiment, rhodium loading / addition was performed as follows: Approximately 0.5% by weight of Rh2O3 was loaded onto 4.19 g of each sample (i.e., mixed oxide core having a rare earth oxide coating) by impregnating it with a predetermined amount of rhodium nitrate solution (rhodium concentration 14.21%). Next, the rhodium nitrate was diluted with water to reach the limiting impregnation point of each composition sample of the present disclosure. The diluted rhodium nitrate solution was added dropwise onto the mixed oxide powder having a rare earth oxide coating while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0075] In a particular embodiment, palladium loading / addition is carried out as follows: Approximately 1.6% by weight of PdO is loaded onto each 7.92 g sample (i.e., mixed oxide core with rare earth oxide coating) by impregnation with a predetermined amount of palladium nitrate solution (palladium concentration 17.99%). The palladium nitrate is diluted in water and prepared to reach the impregnation point humidity of each sample. The diluted palladium nitrate solution is added dropwise onto the mixed oxide powder with rare earth coating while stirring. The powder is then dried and calcined at 550°C for 2 hours.

[0076] The method described herein yields a composition having rhodium or palladium on its surface and exhibiting a higher degree of rhodium or palladium dispersion, the composition having any or all of the properties and characteristics described above.

[0077] The compositions disclosed herein can be used as part of a catalyst system or as elements of a catalyst composition. These catalysts are used for purifying exhaust gases in automobiles and other related applications.

[0078] In the following, the method of the present invention for preparing compositions in which rhodium or palladium is dispersed on a surface, and the characterization thereof, will be described in more detail by examples. However, the scope of the present invention is not limited in any way by these examples.

[0079] Figure 1 is a flowchart showing one embodiment of a method for producing a composition comprising a mixed oxide core having a rare earth oxide coating on its surface and having a high rhodium or palladium dispersion on the surface.

[0080] The rhodium and palladium dispersion in the following examples was measured using the rhodium and palladium dispersion measurement method described above.

[0081] Comparative Example 1: Mixed oxide containing Rh that has not undergone further surface modification (without rare earth oxide coating) The following operations were performed. 1) A mixed oxide (substantially consisting of Ce / Zr / La / Nd, with a ratio of approximately 20.8 wt% Ce, 72.2 wt% Zr, 1.7 wt% La, and 5.3 wt% Nd) was prepared without further surface modification by rare earth coating.

[0082] Rhodium loading / addition was performed as follows: Approximately 0.5% by weight of Rh2O3 was loaded onto the mixed oxide sample by impregnation with a predetermined amount of rhodium nitrate solution. The rhodium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted rhodium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0083] Comparative Example 2: Mixed oxide containing Pd that has not undergone further surface modification (without rare earth oxide coating) The following operations were performed. 1) A mixed oxide consisting of Ce / Zr / La / Nd / Pr was prepared without further surface modification by rare earth coating, with a ratio of approximately 40% by weight of Ce, approximately 50% by weight of Zr, 2% by weight of La (lanthanum), 4% by weight of Nd, and 4% by weight of Pr.

[0084] Palladium was supported / added as follows: Approximately 1.6% by weight of PdO was supported on the mixed oxide sample by impregnating it with a predetermined amount of palladium nitrate solution. The palladium nitrate was diluted with water to reach the impregnation point humidity of each sample in this disclosure. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0085] Example 1: Mixed oxide having an Nd2O3 coating and containing Rh (mixed oxide surface modified with Nd2O3) The following operations were performed. 1) 12.25 g of mixed oxide (composed of Ce / Zr / La / Nd, with approximately 21.4 wt% Ce, 74.4 wt% Zr, 1.8 wt% La, and 2.4 wt% Nd) was divided equally into portions. 2) 1.73 g of Nd nitrate solution (Nd2O3 = 306.0 g / L, density = 1.47 g / mL) was mixed with 3.8 mL of deionized water. 3) Diluted Nd nitrate solution was slowly added to each mixed oxide portion. 4) All parts were combined and mixed to obtain a homogeneous mixture. 5) The powder was calcined at 500°C to obtain an oxide support.

[0086] Rhodium loading / addition was performed as follows: Approximately 0.5% by weight of Rh2O3 was loaded onto 4.19 g of a mixed oxide sample with a rare earth coating by impregnating it with a predetermined amount of rhodium nitrate solution (rhodium concentration 14.21%). Subsequently, the rhodium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted rhodium nitrate solution was added dropwise onto the mixed oxide powder with the rare earth coating while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0087] Example 2: Mixed oxide containing Rh and having Nd2O3 and CeO2 coatings (mixed oxide surface modified with Nd2O3 and CeO2) The following operations were performed. 1) 1.15 g of cerium ammonium nitrate (CAN) and 1.75 g of Nd nitrate solution (Nd2O3 = 297.9 g / L, density = 1.45 g / mL) were mixed with 2.9 mL of deionized water. 2) This Ce / Nd solution was added to 11.88 g of CZO (composed of Ce / Zr / La / Nd, with the ratios of approximately 18.93% by weight of Ce, 76.81% by weight of Zr, 1.81% by weight of La, and 2.45% by weight of Nd) to obtain a homogeneous mixture. 3) To obtain an oxide support, the powder was calcined at 500°C.

[0088] Rhodium loading / addition was performed as follows: Approximately 0.5% by weight of Rh2O3 was loaded onto 4.19 g of a mixed oxide sample with a rare earth coating by impregnating it with a predetermined amount of rhodium nitrate solution (rhodium concentration 14.21%). The rhodium nitrate was diluted with water and prepared to reach the impregnation point humidity of the sample. The diluted rhodium nitrate solution was added dropwise onto the mixed oxide powder with the rare earth coating while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0089] Summary of Comparative Example 1 and Examples 1 and 2 Table 1 below shows the mixed oxide composition before surface modification (i.e., before the addition of the rare earth oxide coating). Comparative Example 1 does not have surface modification (i.e., rare earth oxide coating). [Table 1]

[0090] Table 2 below shows the comparative example 1 and the mixed oxide compositions of Examples 1 and 2 after surface modification (i.e., after the addition of the rare earth oxide coating). [Table 2]

[0091] Table 3 below shows the results of the rhodium dispersion rates in Comparative Example 1 and Examples 1 and 2, which have surface modification (i.e., rare earth oxide coating). [Table 3]

[0092] As summarized in Table 3, Examples 1 and 2 showed significantly higher rhodium dispersion percentages compared to Comparative Example 1, across different aging (additional firing) conditions. These high rhodium dispersion percentages provide improved performance as catalytic materials for catalytic converters and vehicle exhaust gas purification.

[0093] Example 3: Mixed oxide having an Nd2O3 coating and containing Pd (mixed oxide surface modified by Nd2O3) The following operations were performed. Example 3 of the present invention (a composition containing a mixed oxide having an Nd2O3 coating (Nd2O3 surface-modified mixed oxide) and Pd) was carried out by the following procedure. 1) 0.389 g of neodymium nitrate solution (Nd2O3 = 297.9 g / L, density = 1.45 g / mL) was mixed with 4.2 mL of deionized water. 2) To obtain a homogeneous mixture, the obtained neodymium solution was added to 7.92 g of CZO (composed of Ce / Zr / La / Nd / Pr, with the ratios of approximately 40.40 wt% Ce, 50.51 wt% Zr, 2.02 wt% La, 3.03 wt% Nd, and 4.04 wt% Pr). 3) To obtain an oxide support, the powder was calcined at 550°C.

[0094] Palladium was loaded / added as follows: Approximately 1.6% by weight of PdO was loaded onto 7.92 g of a mixed oxide sample by impregnating it with a predetermined amount of palladium nitrate solution (containing 17.99% palladium). Subsequently, the palladium nitrate solution was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was then added dropwise onto the mixed oxide powder while stirring. The resulting powder was then dried and calcined at 550°C for 2 hours.

[0095] Example 4: Mixed oxide having an Nd2O3 coating and containing Pd (mixed oxide surface modified by Nd2O3) The following operations were performed. 1) 0.779 g of Nd nitrate solution (Nd2O3 = 297.9 g / L, density = 1.45 g / mL) was mixed with 3.0 mL of deionized water. 2) To obtain a homogeneous mixture, 7.84 g of CZO (composed of Ce / Zr / La / Nd / Pr, with the ratios of approximately 40.82 wt% Ce, 51.02 wt% Zr, 2.04 wt% La, 2.04 wt% Nd, and 4.08 wt% Pr) was added. The powder was calcined at 500°C to produce an oxide support. 3) To produce an oxide support, the powder was calcined at 500°C.

[0096] Palladium was loaded / added as follows: Approximately 1.6 wt% PdO was loaded onto 7.92 g of a mixed oxide sample by impregnating it with a palladium nitrate solution containing 17.99% palladium. The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0097] Example 5: Mixed oxide having an Nd2O3 coating and containing Pd (mixed oxide surface modified by Nd2O3) The following operations were performed. 1) 1.168 g of Nd nitrate solution (Nd2O3 = 297.9 g / L, density = 1.45 g / mL) was mixed with 3.8 mL of DI water. 2) To obtain a homogeneous mixture, 7.76 g of CZO (composed of Ce / Zr / La / Nd / Pr, with the ratios of approximately 41.24 wt% Ce, 51.55 wt% Zr, 2.06 wt% La, 1.03 wt% Nd, and 4.12 wt% Pr) was added. 3) To produce an oxide support, the powder was calcined at 500°C.

[0098] Palladium was loaded / added as follows: Approximately 1.6% by weight of PdO was loaded by impregnating 7.92 g of a mixed oxide sample with a palladium nitrate solution (17.99% palladium). The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0099] Example 6: Pr6O 11 Mixed oxide (Pr6O) having a coating and containing Pd 11 (Surface-modified mixed oxides) The following operations were performed. 1) 0.562 g of praseodymium nitrate solution (Pr6O 11 A solution with a concentration of 313.85 g / L and a density of 1.47 g / mL was mixed with 6.5 mL of deionized water. 2) To obtain a homogeneous mixture, 11.88 g of CZO (composed of Ce / Zr / La / Nd / Pr, with the ratios of approximately 40.40 wt% Ce, 50.51 wt% Zr, 2.02 wt% La, 4.04 wt% Nd, and 3.03 wt% Pr) was added. 3) To produce an oxide support, the powder was calcined at 500°C.

[0100] Palladium was loaded / added as follows: Approximately 1.6% by weight of PdO was loaded onto 7.92 g of the mixed oxide sample by impregnation with a predetermined amount of palladium nitrate solution (palladium concentration 17.99%). The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0101] Example 7: Pr6O 11 Mixed oxide (Pr6O) having a coating and containing Pd 11 (Mixed oxides modified for surface modification) The following operations were performed. 1) 1.124 g of praseodymium nitrate solution (Pr6O 11 A solution with a concentration of 313.85 g / L and a density of 1.47 g / mL was mixed with 4.6 mL of deionized water. 2) To obtain a homogeneous mixture, 11.76 g of CZO (composed of Ce / Zr / La / Nd / Pr, with the ratios of approximately 40.82 wt% Ce, 51.02 wt% Zr, 2.04 wt% La, 4.08 wt% Nd, and 2.04 wt% Pr) was added. 3) To produce an oxide support, the powder was calcined at 500°C.

[0102] Palladium was loaded / added as follows: Approximately 1.6% by weight of PdO was loaded onto 7.92 g of the mixed oxide sample by impregnation with a predetermined amount of palladium nitrate solution (palladium concentration 17.99%). The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0103] Example 8: Pr6O 11 Mixed oxide (Pr6O) having a coating and containing Pd 11 (Surface-modified mixed oxides) The following operations were performed. 1) 1.686 g of praseodymium nitrate solution (Pr6O 11 A solution with a concentration of 313.85 g / L and a density of 1.47 g / mL was mixed with 5.6 mL of deionized water. 2) To obtain a homogeneous mixture, 11.64 g of CZO (composed of Ce / Zr / La / Nd / Pr, with the ratios of approximately 41.24 wt% Ce, 51.55 wt% Zr, 2.06 wt% La, 4.12 wt% Nd, and 1.03 wt% Pr) was added. 3) To produce an oxide support, the powder was calcined at 500°C.

[0104] Palladium was loaded / added as follows: Approximately 1.6% by weight of PdO was loaded onto 7.92 g of the mixed oxide sample by impregnation with a predetermined amount of palladium nitrate solution (palladium concentration 17.99%). The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0105] Example 9: Mixed oxide having a CeO2 coating and containing Pd (mixed oxide surface modified by CeO2) The following operations were performed. 1) 1.60 g of cerium ammonium nitrate (CAN) was mixed with 5.9 mL of deionized water. 2) This Ce solution was added to 9.50 g of CZO (composed of Ce / Zr / La / Nd / Pr, with the ratios of approximately 36.84 wt% Ce, 52.63 wt% Zr, 2.11 wt% La, 4.21 wt% Nd, and 4.21 wt% Pr) to obtain a homogeneous mixture. 3) To obtain an oxide support, the powder was calcined at 500°C.

[0106] Palladium was loaded / added as follows: Approximately 1.6% by weight of PdO was loaded onto 7.92 g of the mixed oxide sample by impregnation with a predetermined amount of palladium nitrate solution (palladium concentration 17.99%). The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0107] Summary of Comparative Example 2 and Examples 3-9 Table 4 below shows the mixed oxide composition before surface modification (i.e., before the addition of the rare earth oxide coating). Comparative Example 2 does not have surface modification (i.e., rare earth oxide coating). [Table 4]

[0108] Table 5 below shows the mixed oxide compositions of Comparative Example 2 and Examples 3-9 after surface modification (i.e., after the addition of the rare earth oxide coating). [Table 5]

[0109] Table 6 below shows the palladium dispersion results in Comparative Example 3 and Examples 3-9, which were subjected to surface modification (i.e., rare earth oxide coating). [Table 6]

[0110] As summarized in Table 6, Examples 3-9 showed significantly higher percentages of palladium dispersion under different aging (additional firing) conditions compared to Comparative Example 2. These high percentages of palladium dispersion provide improved performance as catalytic converters and catalytic materials for automotive exhaust gas purification.

[0111] Example 10: Mixed oxide having a CeO2 coating and containing Pd (mixed oxide surface modified by CeO2) The following operations were performed. 1) 2.40 g of cerium ammonium nitrate (CAN) was mixed with 8.5 mL of deionized water. 2) This Ce solution was added to 14.25 g of CZO (composed of Ce / Zr / La / Y, with the ratios of approximately 36.84 wt% Ce, 52.63 wt% Zr, 5.26 wt% La, and 5.26 wt% Y) to obtain a homogeneous mixture. 3) To obtain an oxide support, the powder was calcined at 500°C.

[0112] Palladium was loaded / added as follows: Approximately 1.6% by weight of PdO was loaded onto 7.92 g of the mixed oxide sample by impregnation with a predetermined amount of palladium nitrate solution (palladium concentration 17.99%). The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0113] Example 11: Mixed oxide having an Nd2O3 coating and containing Pd (mixed oxide surface modified by Nd2O3) The following operations were performed. 1) 2.34 g of neodymium nitrate solution (Nd2O3 = 297.9 g / L, density = 1.45 g / mL) was mixed with 8.5 mL of deionized water. 2) To obtain a homogeneous mixture, this neodymium solution was added to 15.52 g of CZO (composed of Ce / Zr / La / Nd / Y, with the ratios of approximately 41.24 wt% Ce, 51.55 wt% Zr, 4.12 wt% La, 1.03 wt% Nd, and 2.06 wt% Y). 3) To obtain an oxide support, the powder was calcined at 500°C.

[0114] Palladium was loaded or added as follows: Approximately 1.6% by weight of PdO was loaded onto 7.92 g of a mixed oxide sample by impregnation with a predetermined amount of palladium nitrate solution (palladium concentration 17.99%). The palladium nitrate was diluted with water to reach the impregnation point humidity of the sample. The diluted palladium nitrate solution was added dropwise onto the mixed oxide powder while stirring. The powder was then dried and calcined at 550°C for 2 hours.

[0115] Summary of Examples 10 and 11 Table 7 below shows the mixed oxide compositions of Examples 10 and 11 before surface modification (i.e., before the addition of the rare earth oxide coating). [Table 7]

[0116] Table 8 below shows the mixed oxide compositions of Examples 10 and 11 after surface modification (i.e., addition of rare earth oxide coating). [Table 8]

[0117] Table 9 below shows the results of palladium dispersion in Examples 10 and 11, which were subjected to surface modification (i.e., rare earth oxide coating). [Table 9]

[0118] As shown in Table 9, Examples 10 and 11 exhibited remarkably high palladium dispersion rates across different aging conditions (i.e., additional firing conditions). These high palladium dispersion rates provide the composition with improved performance as a catalytic material for catalytic converters and vehicle exhaust gas purification.

[0119] Unless otherwise explicitly stated, all numerical values ​​such as the amount of components, molecular weight, and reaction conditions used herein and in the claims are understood to be modified by the word "about." Therefore, unless otherwise explicitly stated, the numerical parameters described herein and in the claims are approximations that may vary depending on the properties to be obtained.

[0120] While the numerical ranges and parameters defining the broad scope of the technology are approximations, the numerical values ​​shown in specific examples are described as accurately as possible. However, any numerical value inevitably contains errors due to the standard deviation associated with each test measurement.

[0121] It will be apparent that the compositions and methods described herein are suitable for achieving the effects and advantages described herein. Those skilled in the art will understand that the methods and systems described herein can be implemented in a variety of forms. Therefore, the present invention is not limited by the above examples and illustrations. In this regard, many of the features of the different embodiments described herein can be combined into one embodiment, and other embodiments having fewer or more features than all of the described features are also possible.

[0122] While various embodiments are described for the purposes of this disclosure, various modifications and alterations can be made within the scope of this disclosure. Many other modifications are readily conceivable to those skilled in the art, but these are also included within the spirit of this disclosure.

Claims

1. A composition comprising a mixed oxide core, The mixed oxide core, Based on the total weight of the mixed oxide core, approximately 15% to approximately 60% by weight of cerium oxide, Based on the total weight of the mixed oxide core, approximately 40% to approximately 85% by weight of zirconium oxide, The mixed oxide core contains and does not contain alumina, The mixed oxide core has a rare earth oxide coating, and the rare earth in the rare earth oxide coating is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium, and mixtures thereof. The composition has rhodium or palladium on its surface, and A composition having a higher degree of rhodium or palladium dispersion compared to a composition containing a mixed oxide core without a rare earth oxide coating.

2. A composition comprising a mixed oxide core, The mixed oxide core, Based on the total weight of the mixed oxide core, approximately 15% to approximately 25% by weight of cerium oxide, Based on the total weight of the mixed oxide core, approximately 70% to approximately 85% by weight of zirconium oxide, If necessary, one or more of the following: lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, It is a mixed oxide core that contains alumina and does not contain alumina. The mixed oxide core has a rare earth oxide coating, the rare earth of the rare earth oxide coating is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof, and the composition has rhodium dispersed on its surface, A composition in which the rhodium dispersion is approximately 18.5% to approximately 28.6% after firing in air at 800°C for 2 hours, approximately 14.3% to approximately 21.9% after firing in air at 1000°C for 10 hours, or approximately 10.3% to approximately 16.5% after firing in air at 1100°C for 10 hours.

3. A composition comprising a mixed oxide core, The mixed oxide core, Based on the total weight of the mixed oxide core, approximately 35% to approximately 60% by weight of cerium oxide, Based on the total weight of the mixed oxide core, approximately 40% to approximately 65% ​​by weight of zirconium oxide, If necessary, one or more of the following: lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, It is a mixed oxide core that contains alumina, The composition wherein the mixed oxide core has a rare earth oxide coating, the rare earth of the rare earth oxide coating is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof, and the composition has palladium dispersed on its surface, the degree of palladium dispersion being about 35.0% to about 46.1% after firing in air at 800°C for 2 hours, about 8.5% to about 13.0% after firing in air at 1000°C for 10 hours, or about 3.9% to about 6.0% after firing in air at 1100°C for 10 hours.

4. The mixed oxide core, Approximately 15% to 25% by weight of cerium oxide, Approximately 70% to 85% by weight of zirconium oxide, One or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, The composition according to claim 1, wherein the composition has rhodium on its surface and has a higher degree of rhodium dispersion compared to a composition comprising a mixed oxide core that does not have a rare earth oxide coating.

5. The mixed oxide core, Approximately 35% to 60% by weight of cerium oxide, Approximately 40% to 65% by weight of zirconium oxide, One or more of lanthanum oxide, neodymium oxide, praseodymium oxide, and yttrium oxide, The composition according to claim 1, wherein the composition has palladium on its surface and has a higher degree of palladium dispersion compared to a composition comprising a mixed oxide core that does not have a rare earth oxide coating.

6. The composition according to claim 1 or 4, wherein the composition has rhodium dispersed on its surface, and the degree of rhodium dispersion is about 18.5% to about 28.6% after firing in air at 800°C for 2 hours, about 14.3% to about 21.9% after firing in air at 1000°C for 10 hours, or about 10.3% to about 16.5% after firing in air at 1100°C for 10 hours.

7. The composition according to claim 1 or 5, wherein the composition has palladium dispersed on its surface, and the degree of palladium dispersion is about 35.0% to about 46.1% after firing in air at 800°C for 2 hours, about 8.5% to about 13.0% after firing in air at 1000°C for 10 hours, or about 3.9% to about 6.0% after firing in air at 1100°C for 10 hours.

8. The composition comprises a mixed oxide core substantially containing cerium oxide, zirconium oxide, and additional rare earth oxides selected from the group consisting of lanthanum oxide, neodymium oxide, praseodymium oxide, yttrium oxide, and mixtures thereof, wherein the rare earth oxide coating is one or two of cerium oxide, neodymium oxide, and praseodymium oxide, and if palladium is present, the degree of palladium dispersion is about 35.0 after firing in air at 800°C for 2 hours. The composition according to claim 1, wherein the dispersion is approximately 46.1% to 8.5% to 13.0% after firing in air at 1000°C for 10 hours, or approximately 3.9% to 6.0% after firing in air at 1100°C for 10 hours, and if rhodium is present, the dispersion of rhodium is approximately 18.5% to 28.6% after firing in air at 800°C for 2 hours, approximately 14.3% to 21.9% after firing in air at 1000°C for 10 hours, or approximately 10.3% to 16.5% after firing in air at 1100°C for 10 hours.

9. The composition according to claim 6, wherein the mixed oxide core is substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, and neodymium oxide, and the rare earth coating is either or both of cerium oxide and neodymium oxide.

10. The composition according to claim 7, wherein the mixed oxide core is substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and praseodymium oxide, and the rare earth coating is cerium oxide, neodymium oxide, or praseodymium oxide.

11. The composition according to claim 7, wherein the mixed oxide core is substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and yttrium oxide, and the rare earth coating is cerium oxide or neodymium oxide.

12. The composition according to claim 7, wherein the mixed oxide core is substantially composed of cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide, and the rare earth coating is cerium oxide or neodymium oxide.

13. The composition is Based on the total weight of the aforementioned composition, approximately 20% to approximately 25% by weight of cerium oxide, Based on the total weight of the aforementioned composition, a rare earth oxide coating of about 1% to about 10% by weight is provided. The composition according to claim 1, comprising and having rhodium on the surface.

14. The composition is Based on the total weight of the aforementioned composition, approximately 40% to approximately 60% by weight of cerium oxide, Based on the total weight of the aforementioned composition, a rare earth oxide coating of about 1% to about 10% by weight is provided. The composition according to claim 1, comprising and having palladium on the surface.

15. The composition according to any one of claims 1 to 11, wherein the rare earth oxide coating is in an amount of about 1% to about 10% by weight based on the total weight of the composition.

16. The composition according to claim 15, wherein the rare earth oxide coating is a single rare earth oxide having the rare earth selected from the group consisting of cerium, lanthanum, neodymium, and praseodymium, and the rare earth oxide coating is in an amount of about 1% to about 5% by weight based on the total weight of the composition.

17. The composition according to claim 15, wherein the rare earth oxide coating consists of two rare earth oxides having the rare earth selected from the group consisting of cerium, lanthanum, neodymium, and praseodymium, and each rare earth oxide in the coating is present in an amount of about 1% to about 5% by weight based on the total weight of the composition.

18. The mixed oxide core is CeO ２ and ZrO ２ and further includes at least one of La ２ O ３ , Y ２ O ３ , Nd ２ O ３ and Pr ６ O １１ , and the rare earth oxide coating is one or two of CeO ２ , Nd ２ O ３ and Pr ６ O １１ The composition according to any one of claims 1 to 7.

19. The rhodium or palladium present as an oxide, and the oxide is present in an amount of about 0.5% by weight of Rh based on the total weight of the composition. ２ O ３ Or the composition according to claim 1, comprising about 1.6% by weight of PdO.

20. A catalyst composition comprising the composition according to any one of claims 1 to 19.

21. A method for producing a composition, comprising the following steps. (a) A step of providing a mixed oxide powder of cerium oxide, zirconium oxide, and optionally one or more of neodymium oxide, lanthanum oxide, praseodymium oxide, and yttrium oxide. (b) In the step of dissolving a rare earth salt in water, the rare earth salt is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof in order to obtain a rare earth solution, (c) In order to obtain a homogeneous powder mixture, the rare earth solution and the mixed oxide powder are mixed and stirred. (d) The homogeneous powder mixture is calcined at approximately 400°C to approximately 600°C for approximately 2 to approximately 5 hours to obtain a mixed oxide core having a rare earth oxide coating on its surface, wherein the rare earth coating is selected from the group consisting of cerium, lanthanum, neodymium, praseodymium, yttrium and mixtures thereof. (e) the step of adding a rhodium or palladium salt solution to the mixed oxide core having the rare earth oxide coating, and (f) A method comprising the step of firing at approximately 500°C to approximately 650°C for approximately 2 to 5 hours to obtain a composition containing a mixed oxide core having a rare earth oxide coating on its surface, and having a higher degree of rhodium or palladium dispersion compared to a composition containing a mixed oxide core without a rare earth oxide coating.

22. The method according to claim 21, wherein the rare earth salt in step (b) is a cerium salt, a neodymium salt, a praseodymium salt, or a mixture thereof, and the rare earth oxide coating is cerium oxide, neodymium oxide, praseodymium oxide, or a combination thereof.

23. The method according to claim 22, wherein the salt is a nitrate.

24. The mixed oxide powder comprises cerium oxide, zirconium oxide, neodymium oxide, and lanthanum oxide, and a rhodium salt is added in step (e), or The mixed oxide powder comprises cerium oxide, zirconium oxide, neodymium oxide, lanthanum oxide, and praseodymium oxide, and a palladium salt is added in step (e), or The mixed oxide powder comprises cerium oxide, zirconium oxide, neodymium oxide, lanthanum oxide, and yttrium oxide, and a palladium salt is added in step (e), or The method according to claim 21, wherein the mixed oxide powder comprises cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide, and a palladium salt is added in step (e).

25. The firing in step (d) is 2% O ２ and 98% of N ２ The method according to claim 21, which is carried out in a mixed gas.

26. A composition prepared by the method described in any one of claims 21 to 25.

27. A catalyst composition comprising the composition described in claim 26.

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