Three-way conversion catalysts containing ceria-rich ceria-alumina composites

Abstract

The present invention provides platinum group metal catalyst compositions with high ceria content ceria-alumina composite supports, along with catalytic articles and gas treatment systems containing the catalyst compositions. The present invention also provides methods of using the catalyst compositions, catalytic articles and systems for exhaust gas treatment.

Description

THREE-WAY CONVERSION CATALYSTS CONTAINING CERIA-RICH CERIA- ALUMINA COMPOSITES BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0001] The present invention is directed to platinum group metal (PGM) catalysts and more specifically to PGM catalysts supported on high ceria-content ceria-alumina composite materials. BACKGROUND INFORMATION

[0002] Since the 1970s, three-way conversion (TWC) catalysts have been adapted for extensive applications in pollutant remediation, including NO, CO and hydrocarbon (HC) removal from automotive engine exhaust. While modern TWC catalysts typically utilize Pd and Rh as active catalytic components, increasingly stringent global emissions regulations coupled with growing demand for platinum group metals (PGM) have resulted in a supply shortage for these two metals, especially for Rh. These conditions have created an enormous incentive for the industry to diminish PGM loading in TWC catalysts and to replace part of Pd with less expensive Pt in TWC catalysts.

[0003] Nonetheless, because PGM loading often correlates with catalytic activity, diminishing PGM loading will likely require more active and stable catalysts. Similarly, widescale adoption of Pt TWC catalysts has been hampered by numerous physical limitations. While Pt has been extensively utilized as a diesel oxidation catalyst, its relatively low stability in gasoline exhaust has limited Pt TWC applications. In particular, Pt catalysts often exhibit susceptibility to thermal deactivation, sintering, and deterioration under operating conditions that limit their lifespan, leading Pd and Rh to be preferred for many applications. Accordingly, there exists a need for PGM, and in particular Pt, catalysts with improved activities and stabilities. SUMMARY OF THE INVENTION

[0004] It was surprisingly discovered herein that ceria-alumina supports with greater than about 50% ceria content increase the activities and stabilities of PGMs relative to reference catalysts with alumina or low-ceria content (e.g., 20% ceria) ceria-alumina supports. These performance advantages are demonstrated herein with reactor test data for powder and monolith core catalysts and engine test data with fully formulated, full-size catalysts. Suitable catalyst and performance features of the present invention are described herein.

[0005] In one aspect, the present invention provides a catalyst composition with one or more platinum group metals (PGM) and a ceria-alumina composite comprising ceria and alumina in a weight ratio of between 1:1 and 19:1; wherein the one or more platinum group metals are supported on the ceria-alumina composite.

[0006] In some embodiments, the platinum group metal is platinum, rhodium, or a combination thereof. In some embodiments, the catalyst composition does not include palladium. In some embodiments, the platinum group metal is between about 0.025 and 5 weight percent (wt%) of the catalyst. In some embodiments, the platinum group metal is: i) rhodium present at about 0.05 to 1 weight percent of the catalyst composition; ii) platinum present at about 0.25 to 4 weight percent of the catalyst composition; iii) palladium present at about 0.25 to 4 weight percent of the catalyst composition; iv) platinum and palladium each present at about 0.25 to 2 weight percent of the catalyst composition; v) platinum present at about 0.25 to 2 weight percent of the catalyst and rhodium present at about 0.05 to 1 weight percent of the catalyst composition; vi) palladium present at about 0.25 to 2 weight percent of the catalyst and rhodium present at about 0.05 to 1 weight percent of the catalyst composition; or vii) platinum present at about 0.25 to 2 weight percent of the catalyst, palladium present at about 0.25 to 2 weight percent of the catalyst, and rhodium present at about 0.05 to 1 weight percent of the catalyst composition.

[0007] In some embodiments, a weight ratio of ceria to alumina in the ceria-alumina composite is between 1:1 and 3:1. In some embodiments, a weight ratio of ceria to alumina in the ceria-alumina composite is between 13:7 to 3:1. In some embodiments, the catalyst composition includes between about 10% and 80% of the ceria-alumina composite by weight.

[0008] In some embodiments, the catalyst composition also includes an oxygen storage component. In some embodiments, the platinum group metal is supported on the oxygen storage component. In some embodiments, the oxygen storage component includes Y2O3, Nd2O3, La2O3, Pr6O11, or a combination thereof. In some embodiments, the oxygen storage component includes between about 10 and 70 weight percent ceria.

[0009] In another aspect, the present invention provides a catalytic article that includes a catalyst of the present disclosure.

[0010] In a further aspect, the present invention provides a layered catalytic article with a substrate, a first layer that is disposed on the substrate and includes a catalyst composition of the present disclosure, and a second layer disposed on the first layer comprising a platinum group metal supported on a ceria-alumina composite.

[0011] In some embodiments, the second layer further comprises an oxygen storage component. In some embodiments, the ceria-alumina composite of the second layer includes less than 30% ceria by weight. In some embodiments, the platinum group metal of the second layer is platinum, rhodium, or a combination thereof.

[0012] In some embodiments, the first layer includes a second catalyst composition with a platinum group metal supported on alumina in a first zone and the catalyst composition of the present disclosure in a second zone. In some embodiments, the second catalyst composition further includes an oxygen storage component. In some embodiments, the alumina component further comprises up to 20% ceria by weight. In some embodiments, the first zone is an inlet zone and the second zone is an outlet zone.

[0013] In some embodiments, the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate and a woven fiber substrate.

[0014] In an additional aspect, the present invention provides an exhaust gas treatment system for internal combustion engines that includes a catalytic composition, catalytic article, or layered catalytic article of the present invention.

[0015] In another aspect, the present invention provides a method of treating a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxide by contacting said exhaust stream with a catalytic composition, catalytic article, or layered catalytic article of the present invention.

[0016] In a further aspect, the present invention provides a method of reducing hydrocarbons, carbon monoxide, and nitrogen oxide levels in a gaseous stream by contacting the gaseous stream with a catalytic composition, catalytic article, or layered catalytic article of the present invention.

[0017] In another aspect, the present invention provides a use of a catalytic composition, catalytic article, or layered catalytic article of the present invention for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGS. 1A-C are plots of CO, NO, and HC conversion by multiple Rh catalysts as a function of temperature. The Rh catalysts included 0.5 weight percent Rh supported on Al2O3, a ceria-alumina composite with 20 weight percent ceria, a ceria alumina composite with 50 weight percent ceria, and a ceria alumina composite with 70 weight percent ceria. FIG. 1A is a plot of CO conversion by the catalysts. FIG. 1B is a plot of NO conversion by the catalysts. FIG. 1C is a plot of HC conversion by the catalysts.

[0019] FIGS. 2A-C are plots of CO, NO, and HC conversion by multiple Pt catalysts as a function of temperature. The Pt catalysts included 2 weight percent Pt supported on Al2O3, a ceria-alumina composite with 20 weight percent ceria, and a ceria alumina composite with 70 weight percent ceria. FIG. 2A is a plot of CO conversion by the catalysts. FIG.2B is a plot of NO conversion by the catalysts. FIG. 2C is a plot of HC conversion by the catalysts.

[0020] FIGS. 3A-C are plots of CO, NO, and HC conversion by multiple Pd catalysts as a function of temperature. The Pd catalysts included 1 weight percent Pd supported on Al2O3, a ceria-alumina composite with 20 weight percent ceria, a ceria alumina composite with 30 weight percent ceria, and a ceria alumina composite with 50 weight percent ceria. FIG. 3A is a plot of CO conversion by the catalysts. FIG. 3B is a plot of NO conversion by the catalysts. FIG. 3C is a plot of HC conversion by the catalysts.

[0021] FIGS 4A-C are plots of CO, NO, and HC conversion by multiple monolith core catalysts as a function of temperature. FIG.4A is a plot of CO conversion by the monolith core catalysts. FIG.4B is a plot of NO conversion by the monolith core catalysts. FIG.4C is a plot of HC conversion by the monolith core catalysts.

[0022] FIG. 5 is a bar graph showing non-methane hydrocarbon (MNHC) and NOx tailpipe emissions in systems with fully formulated full-sized catalysts.

[0023] FIG. 6 is a schematic representation of a zoned, layered catalyst design, consistent with the present invention.

[0024] FIG. 7 is a schematic representation of a single layer uniform catalyst design consistent with the present invention.

[0025] FIG. 8 is a schematic representation of a zoned, layer catalyst reference, which is to be compared with that represented in Fig. 6. DETAILED DESCRIPTION OF THE INVENTION

[0026] Before the present compositions and methods are described, it is to be understood that this invention is not limited to particular compositions, methods, and experimental conditions described, as such compositions, methods, and conditions may vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only in the appended claims.

[0027] As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, references to “the method” includes one or more methods, and / or steps of the typedescribed herein which will become apparent to those persons skilled in the art upon reading this disclosure and so forth.

[0028] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0029] As used herein, the term “about” in association with a numerical value is meant to include any additional numerical value reasonably close to the numerical value indicated. For example, and based on the context, the value can vary up or down by 5-10%. For example, for a value of about 100, means 90 to 110 (or any value between 90 and 110).

[0030] As used herein and in the claims, the terms “comprising,” “containing,” and “including” are inclusive, open-ended and do not exclude additional unrecited elements, compositional components or method steps. Accordingly, the terms “comprising” and “including” encompass the comparably more restrictive terms “consisting of” and “consisting essentially of.”

[0031] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

[0032] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, it will be understood that modifications and variations are encompassed within the spirit and scope of the instant disclosure. The preferred methods and materials are now described.

[0033] The present invention is based on the surprising discovery that high ceria content ceria-alumina supports enhance PGM catalyst lifespan and activity. Leveraging this discovery, the present invention provides PGM catalysts supported on high ceria content ceria alumina supports. Stemming from these advantageous properties, the catalysts of the present invention can have lower PGM and in particular lower Pd loading than conventional PGM catalysts. The catalysts can be incorporated into catalytic articles useful for CO, NO, and HC remediation from exhaust gas streams.

[0034] In one aspect, the present invention provides a catalyst composition with one or more platinum group metals (PGM) and a ceria-alumina composite with ceria (CeO2) and alumina (Al2O3) in a weight ratio of between 1:1 and 19:1, wherein the one or more platinum group metals are supported on the ceria-alumina composite. As disclosed herein, this catalystcomposition can exhibit high activities for a broad range of processes, including for CO, NO, and HC conversion, enabling low PGM loading and thus reduced catalyst costs.

[0035] Furthermore, this catalyst composition can exhibit high degrees of stability in a range of operating conditions. For example, as outlined in EXAMPLE 12, ceria-alumina supports can exhibit low specific surface area (SSA) reductions following 4 hours of calcination at 1000°C, demonstrating that the supports maintain fidelity through harsh operating conditions. In some embodiments, a catalyst composition disclosed herein undergoes less than about 70%, less than about 60%, less than about 50%, less than about 45%, or less than about 40% SSA reduction (%) following 4 hours of calcination at 1000°C.

[0036] Accordingly, this invention addresses the need for lower PGM loading and for partial Pd replacement in TWC catalysts. CERIA-ALUMINA COMPOSITES

[0037] As used herein, the term “ceria-alumina composite” denotes a single composite material in which CeO2 and Al2O3 are distributed in bulk (e.g., as particles or clusters). Ceria- alumina composites consistent with the present invention include mixed oxides in which CeO2and Al2O3 have distinct chemical and physical states and exhibit separate analytical (e.g., x- ray powder diffraction) profiles. Any physical state of CeO2 or the combination of the states can exist or coexist on the surface or in the interior of the composite material. In many embodiments, the ceria-alumina composite comprises at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, at least about 99.5%, or at least about 99.9% CeO2 and Al2O3 by weight. In some embodiments, the ceria-alumina composite consists of or consists essentially of CeO2and Al2O3. Alternatively, the ceria- alumina composite can include a dopant, an additional metal oxide, an impurity, or a combination thereof.

[0038] It was surprisingly discovered herein that high ceria content ceria-alumina composites confer high stabilities and catalytic activities to supported platinum group metals such as platinum, rhodium, and palladium. Accordingly, in many embodiments, the ratio of CeO2 to Al2O3in the ceria-alumina composite is between 1:1 and 10:1, between 1:1 and 8:1, between 1:1 and 6:1, between 1:1 and 5:1, between 1:1 and 4:1, between 1:1 and 3:1, between 1:1 and 2:1, between 1:1 and 3:2, between 3:2 and 19:1, between 3:2 and 10:1, between 3:2 and 8:1, between 3:2 and 6:1, between 3:2 and 5:1, between 3:2 and 4:1, between 3:2 and 3:1, between 13:7 and 19:1, between 13:7 and 10:1, between 13:7 and 8:1, between 13:7 and 6:1, between13:7 and 5:1, between 13:7 and 4:1, between 13:7 and 3:1, between 13:7 and 3:1, between 7:3 and 19:1, between 7:3 and 10:1, between 7:3 and 8:1, between 7:3 and 6:1, between 7:3 and 5:1, between 7:3 and 4:1, or between 7:3 and 3:1. In particular embodiments, the ratio of CeO2to Al2O3 in the ceria-alumina composite is between 31:19 and 4:1, between 31:19 and 39:11, between 31:19 and 3:1, between 13:7 and 4:1, between 13:7 and 39:11, between 13:7 and 3:1, or between 27:13 and 29:11.

[0039] In some embodiments, the ceria-alumina composite includes a dopant. As non- limiting examples, the dopant may be selected from zirconia, lanthana, titania, hafnia, magnesia, calcia, strontian, baria or any combination thereof. The total amount of dopant in the ceria-alumina composite, when present, is preferably in the range of 0.001 to 15 weight percent (wt%), 0.001 to 0.1 wt%, 0.1 to 2.5 wt%, 0.5 to 5 wt%, 1 to 10 wt%, or 2.5 to 15 wt% based on the total weight of the ceria-alumina composite.

[0040] In some embodiments, the catalyst composition includes between about 10% and 80% of the ceria-alumina composite by weight. For example, the catalyst composition can include between about 10% and 25%, between about 20% and 40%, between about 25% and 50%, between about 30% and 60%, between about 40% and 80%, or between about 60% and 80% of the ceria-alumina composite by weight. PLATINUM GROUP METALS

[0041] As used herein, the term “platinum group metal” (PGM) can denote Ru, Rh, Os, Ir, Pd, Pt, Au, and combinations thereof. However, in many embodiments, the PGM is Rh, Pd, Pt, or a combination thereof. In some embodiments, the platinum group metal is platinum, rhodium, or a combination thereof. In some embodiments, the platinum group metal does not include palladium. As used herein, the terms “does not include”, “does not comprise”, and “essential free of” denote that a species was not added to a composition, article, or layer, and is either not present or present in trace amounts (e.g., < 0.001 wt%). In some embodiments, the platinum group metal is one of platinum, rhodium, or palladium. In some embodiments, the platinum group metal is platinum. In some embodiments, the platinum group metal is rhodium. In some embodiments, the platinum group metal is palladium.

[0042] The term “platinum group metal” allows for the presence of the PGM in any valence state. However, in specific embodiments, a PGM in a catalyst, composition, layer, article, or other structure disclosed herein denotes a catalytically active form of the PGM. For example, in some embodiments, a PGM was converted to a catalytically active form through calcination. In some embodiments, the PGM is in a metallic form (e.g., with zero valence) or in an oxide form.

[0043] Leveraging the discovery that high ceria-content ceria-alumina supports enhance PGM activity, catalysts of the present disclosure can include lower PGM loading than conventional TWC catalysts. In some embodiments, the platinum group metal is about 0.025 to 5 weight percent of the catalyst. In some embodiments, the platinum group metal is about 0.025 to 0.5, about 0.05 to 0.5, about 0.1 to 1, about 0.25 to 1.5, about 0.5 to 1.5, about 1 to 2, about 1 to 2.5, about 1.5 to 3, 2 to 4, or 2.5 to 5 weight percent of the catalyst.

[0044] In certain embodiments, the platinum group metal is rhodium present at about 0.05 to 1 weight percent of the catalyst composition, about 0.05 to 0.25 weight percent of the catalyst composition, about 0.1 to 0.4 weight percent of the catalyst composition, about 0.25 to 0.5 weight percent of the catalyst composition, about 0.3 to 0.6 weight percent of the catalyst composition, about 0.4 to 0.8 weight percent of the catalyst composition, or about 0.5 to 1 weight percent of the catalyst composition.

[0045] In other embodiments, the platinum group metal is platinum present at about 0.25 to 4 weight percent of the catalyst composition, about 0.25 to 1 weight percent of the catalyst composition, about 0.5 to 1.5 weight percent of the catalyst composition, about 0.5 to 2 weight percent of the catalyst composition, about 0.75 to 2.25 weight percent of the catalyst composition, about 1 to 2.5 weight percent of the catalyst composition, about 1.5 to 3 weight percent of the catalyst composition, or about 2 to 4 weight percent of the catalyst composition.

[0046] In further embodiments, the platinum group metal is palladium present at about 0.25 to 4 weight percent of the catalyst composition, about 0.25 to 1 weight percent of the catalyst composition, about 0.5 to 1.5 weight percent of the catalyst composition, about 0.5 to 2 weight percent of the catalyst composition, about 0.75 to 2.25 weight percent of the catalyst composition, about 1 to 2.5 weight percent of the catalyst composition, about 1.5 to 3 weight percent of the catalyst composition, or about 2 to 4 weight percent of the catalyst composition.

[0047] In additional embodiments, the platinum group metal is platinum and palladium each present at about 0.25 to 2 weight percent of the catalyst composition, about 0.25 to 0.75 weight percent of the catalyst composition, about 0.5 to 1 weight percent of the catalyst composition, about 0.75 to 1.5 weight percent of the catalyst composition, or about 1 to 2 weight percent of the catalyst composition.

[0048] In certain embodiments, the platinum group metal is platinum present at about 0.25 to 2 weight percent of the catalyst composition and rhodium present at about 0.05 to 1 weight percent of the catalyst composition. For example, in some embodiments, the platinum group metal is platinum present at about 0.25 to 1 weight percent of the catalyst composition and rhodium present at about 0.05 to 0.25 weight percent of the catalyst composition, the platinumgroup metal is platinum present at about 0.5 to 1.5 weight percent of the catalyst composition and rhodium present at about 0.2 to 0.6 weight percent of the catalyst composition, or the platinum group metal is platinum present at about 1 to 2 weight percent of the catalyst composition and rhodium present at about 0.5 to 1 weight percent of the catalyst composition.

[0049] In certain embodiments, the platinum group metal is palladium present at about 0.25 to 2 weight percent of the catalyst composition and rhodium present at about 0.05 to 1 weight percent of the catalyst composition. For example, in some embodiments, the platinum group metal is palladium present at about 0.25 to 1 weight percent of the catalyst composition and rhodium present at about 0.05 to 0.25 weight percent of the catalyst composition, the platinum group metal is palladium present at about 0.5 to 1.5 weight percent of the catalyst composition and rhodium present at about 0.2 to 0.6 weight percent of the catalyst composition, or the platinum group metal is palladium present at about 1 to 2 weight percent of the catalyst composition and rhodium present at about 0.5 to 1 weight percent of the catalyst composition.

[0050] In some embodiments, the platinum group metal is platinum present at about 0.25 to 2 weight percent of the catalyst, palladium present at about 0.25 to 2 weight percent of the catalyst, and rhodium present at about 0.05 to 1 weight percent of the catalyst composition. For example, in some embodiments, the platinum group metal is platinum present at about 0.25 to 1 weight percent of the catalyst, palladium present at about 0.25 to 1 weight percent of the catalyst, and rhodium present at about 0.05 to 0.5 weight percent of the catalyst composition. In other embodiments, the platinum group metal is platinum present at about 1 to 2 weight percent of the catalyst, palladium present at about 1 to 2 weight percent of the catalyst, and rhodium present at about 0.5 to 1 weight percent of the catalyst composition. OXYGEN STORAGE COMPONENTS

[0051] In some embodiments, the catalyst composition also includes an oxygen storage component (OSC). In such embodiments, the PGM can be supported on the ceria-alumina composite and the OSC. As used herein, the term “oxygen storage component” (OSC) denotes a solid solution that includes ceria and zirconia and is capable of storing and releasing oxygen upon changes in oxygen partial pressure within an operating environment. This can be achieved by changes in valence by an OSC metal and concomitant oxidation or reduction of oxygen containing species. For example, ceria can cycle between a +4 and +3 redox couple, releasing oxygen when the environment is reducing with some Ce changing oxidation state from 4+ to 3+, and absorbing oxygen when the environment is oxidizing with some Ce changing oxidation state from 3+ to +4.

[0052] OSCs can stabilize oxygen levels in an exhaust by releasing oxygen under a net reducing (or fuel-rich) environment and absorbing oxygen in a net oxidizing (or fuel-lean) environment. This property can be useful in a range of operating environments that include fluctuating oxygen levels. As an example, in gasoline vehicles, exhaust gas content actively perturbs around a lambda value of 1. Here, the lambda value is defined by the ratio of oxygen content to the combination of CO and HC content. Modern gasoline vehicles typically utilize two lambda sensors, one in front of the TWC catalyst and a second behind the TWC catalyst. A lambda value of greater than 1 in front of the TWC indicates that the engine is operating with more oxygen than is needed for combustion, which promotes low CO / HC emissions. Conversely, a lambda value of less than 1 in front of the TWC means that the engine is operating with an insufficient amount of oxygen for combustion, leading to higher CO and HC emissions but diminishing NOx emissions. To balance the overall CO / HC / NOx emissions, modern gasoline vehicles typically control lambda values to remain close to 1. However, scenarios with frequent acceleration (e.g., as is frequent in stop-and-go traffic) can cause wide perturbations in lambda values and poor catalyst performance. Accordingly, an oxygen storage compound is often included in the TWC to minimize lambda perturbations. While ceria typically confers oxygen storage capacity, it has a poor thermal stability, and is therefore often thermally stabilized with zirconia and rare earth metal dopants.

[0053] In many embodiments, the oxygen storage component includes between about 10 and 70 weight percent ceria. In some embodiments, the oxygen storage component includes between about 10 and 25 weight percent, between about 10 and 40 weight percent, between about 15 and 50 weight percent, between about 20 and 60 weight percent, between about 30 and 60 weight percent, or between about 40 and 70 weight percent ceria. In some embodiments, the oxygen storage component includes between about 10 and 80 weight percent zirconia, between about 10 and 30 weight percent zirconia, between about 10 and 50 weight percent zirconia, between about 25 and 50 weight percent zirconia, between about 30 and 60 weight percent zirconia, between about 40 and 80 weight percent zirconia, between about 50 and 80 weight percent zirconia, or between about 60 and 80 weight percent zirconia. In some embodiments, the catalyst composition includes between about 10 and 80 weight percent of the oxygen storage component, between about 10 and 30 weight percent of the oxygen storage component, between about 10 and 50 weight percent of the oxygen storage component, between about 25 and 50 weight percent of the oxygen storage component, between about 30 and 60 weight percent of the oxygen storage component, between about 40 and 80 weight percent of the oxygen storage component, between about 50 and 80 weight percent of theoxygen storage component, or between about 60 and 80 weight percent of the oxygen storage component. In some embodiments, the oxygen storage component comprises ceria, zirconia, and at least one additional metal oxide. For example, in certain embodiments, the oxygen storage component includes Y2O3, Nd2O3, La2O3, Pr6O11, or a combination thereof. CATALYTIC ARTICLES

[0054] Further disclosed herein is a catalytic article containing a catalyst composition of the present invention disposed on a substrate, for example as a washcoat or other adherent layer containing or consisting of the catalyst composition. As used herein, the term “washcoat” has its usual meaning in the art of a thin, adherent coating of a catalytic or other material applied to a substrate material. Generally, a washcoat is formed by preparing a slurry containing a certain solid content (e.g., 15-60% by weight) of particles in a liquid vehicle, which is then coated onto a substrate and dried to provide a washcoat layer.

[0055] In this catalytic article, the catalyst composition typically includes a degree of porosity that enables passage of a gas stream during treatment. The porosity, surface area, and thickness of the catalyst composition can be tuned to achieve desired flow rates, gas residence times, and catalytic performance by the article. The catalytic article can include a single layer or multiple layers of the catalytic composition. Optionally, the catalytic article can include two or more layers with different catalyst compositions.

[0056] FIG. 7 provides an example of a single layer uniform catalyst design consistent with the present disclosure. In this figure, Ce-Al (1) is a CeO2 / Al2O3 mixed oxide with CeO2 content lower than 20% by weight; Ce-Al (2) is a CeO2 / Al2O3mixed oxide with CeO2content higher than 50% by weight; OSC is a rare earth metal doped Ce / Zr mixed oxide; “additive” may be various Ba compounds or La compounds; and binder may be an alumina or zirconia-based compound.

[0057] For example, in one aspect, the present invention provides a layered catalytic article with a substrate, a first layer disposed on the substrate containing a high ceria content catalyst composition as disclosed herein, and a second layer disposed on the first layer containing a catalyst comprising a platinum group metal supported on a ceria-alumina component. The high ceria content catalyst composition can be a catalyst composition that include a ceria-alumina composite with a ceria to alumina ratio of between 1:1 and 19:1, an oxygen storage component, and additional dopants or constituents as disclosed herein. In some embodiments, the layered catalytic article comprises an additional layer that includes a catalyst consistent with the present invention.

[0058] The ceria-alumina composite in the second layer can include low ceria-content relative to the ceria-alumina composite in the catalyst in the first layer, such as less than about 60% ceria by weight, less than about 50% ceria by weight, less than about 40% ceria by weight, less than about 30% ceria by weight, less than about 25% ceria by weight, less than about 20% ceria by weight, less than about 15% ceria by weight, less than about 10% ceria by weight, or less than about 5% ceria by weight. Alternatively or in addition thereto, the ceria-alumina composite in the second layer can have a ceria-to-alumina ratio of 3:2 to 1:19, 3:2 to 1:9, 1:1 to 1:19, 1:1 to 1:9, 2:3 to 1:19, 2:3 to 1:9, 3:7 to 1:19, 3:7 to 1:9, 1:4 to 1:19, or 1:4 to 1:9.

[0059] The second layer can also include an oxygen storage component. In such cases, the platinum group metal in the second layer can be supported on the oxygen storage component and on the ceria-alumina composite. The oxygen storage component can be between about 10% and 80% of the second layer by weight. For example, the second layer can include between about 10% and 25%, between about 20% and 40%, between about 25% and 50%, between about 30% and 60%, between about 40% and 80%, or between about 60% and 80% of the oxygen storage component by weight.

[0060] The platinum group metal in the second layer can be the same as or different than the platinum group metal in the catalyst composition of the first layer. In some embodiments, the platinum group metal in the second layer is platinum, palladium, rhodium, or a combination thereof. In other embodiments, the second layer does not include palladium. For example, the platinum group metal in the second layer can be platinum, rhodium, or a combination thereof. In some embodiments, the platinum group metal in the second layer is platinum present at about 0.25 to 4 weight percent, about 0.25 to 1 weight percent, about 0.5 to 1.5 weight percent, about 0.5 to 2 weight percent, about 0.75 to 2.25 weight percent, about 1 to 2.5 weight percent, about 1.5 to 3 weight percent, or about 2 to 4 weight percent. In some embodiments, the platinum group metal in the second layer is rhodium present at about 0.05 to 1 weight percent, about 0.05 to 0.25 weight percent, about 0.1 to 0.4 weight percent, about 0.25 to 0.5 weight percent, about 0.3 to 0.6 weight percent, about 0.4 to 0.8 weight percent, or about 0.5 to 1 weight percent. In some embodiments, the platinum group metal in the second layer is platinum present at about 0.25 to 2 weight percent of the catalyst composition and rhodium present at about 0.05 to 1 weight percent of the catalyst composition.

[0061] One or more layers of the layered catalytic article can be zoned. Two zones can be disposed in a linearly, radially, or in a complex pattern. As used herein, the term “zoned” denotes two or more spatially defined regions with distinct physical properties and / or compositions. The term “inlet zone” denotes that a zone is exposed to a region or end of a layerthrough which gas enters. The term “outlet zone” denotes that a zone is exposed to a region or end of a layer through which gas exits. In the context of the present invention, where a catalytic article includes two zones (e.g., within a layer of a catalytic article), the term “first zone” is interchangeably used for “inlet zone” or “front zone” and the term “second zone” is interchangeably used for “outlet zone” or “rear zone”.

[0062] In a particular embodiment, the first layer includes a first zone with a second catalyst that includes a platinum group metal supported on alumina and a second zone with the catalyst composition of the present disclosure that includes the high ceria-content ceria-alumina composite. An example of such a zoned and layered design is illustrated in FIG. 6, which depicts the substrate 601, first 602 and second 603 zones of a first layer, and a second layer 604. In this figure, Ce-Al (1) is a CeO2 / Al2O3 mixed oxide with CeO2 content lower than 20% by weight; Ce-Al (2) is a CeO2 / Al2O3mixed oxide with CeO2content higher than 50% by weight; OSC is a rare earth metal doped Ce / Zr mixed oxide; “additive” may be various Ba compounds or La compounds; and “binder” may be alumina or zirconia-based compounds. In this embodiment, the first zone is an inlet zone and the second zone is an outlet zone. The alumina of the first catalyst can be ceria-free, can include up to 10% ceria by weight, up to 20% ceria by weight, up to 30% ceria by weight, or up to 40% ceria by weight. The first catalyst can also include an oxygen storage component on which the platinum group metal is supported. The catalyst can include between about 10% and 25%, between about 20% and 40%, between about 25% and 50%, between about 30% and 60%, between about 40% and 80%, between about 60% and 80%, or between about 10% and 80% of the oxygen storage component by weight.

[0063] The substrate can be any substrate suitable for PGM catalyst and / or TWC catalyst operating conditions. As non-limiting examples, the substrate can be a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate or a woven fiber substrate. In some embodiments, the substrate is monolithic. In some embodiments, the substrate has a honeycomb structure. GAS TREATMENT SYSTEMS AND METHODS OF USE

[0064] In another aspect of the present invention, there is also provided an exhaust gas treatment system for internal combustion engines, said system including the catalyst, catalytic article, or layered catalytic article described hereinabove. The catalyst, catalytic article, or layered catalytic article may be placed in a close-coupled position, wherein hereinafter can denote close proximity to an engine to facilitate faster heat transfer from the engine and thus faster attainment of reaction temperatures during operation. Due to their proximity to theengine, close-coupled catalysts are typically required to be stable at high temperatures, rendering the catalysts of the present invention as suitable for such uses. In general, the close- coupled catalyst is placed within three feet, more specifically, within one foot of the engine, and even more specifically, less than six inches from the engine. Close-coupled catalysts are often attached directly to the exhaust gas manifold.

[0065] The catalytic article of the invention can also be used as part of an integrated exhaust system with one or more additional components for the treatment of exhaust gas emissions. For example, the exhaust system also known as emission treatment system may further include a close coupled TWC catalyst, an underfloor TWC catalyst, a catalyzed soot filter (CSF) component, and / or a selective catalytic reduction (SCR) catalytic article. The preceding list of components is merely illustrative and should not be taken as limiting the scope of the invention.

[0066] In another aspect, the present invention provides a method of treating a gaseous exhaust stream with hydrocarbons, carbon monoxide, and nitrogen oxide by contacting said exhaust stream with the catalyst composition, catalytic article, or layered catalytic article according to the present invention or the exhaust gas treatment system according to the present invention. The present invention also provides a method of reducing hydrocarbons, carbon monoxide, and nitrogen oxide levels in a gaseous exhaust stream by contacting a gaseous exhaust stream with the catalyst composition, catalytic article, or layered catalytic article according to the present invention or the exhaust gas treatment system according to the present invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxide in the exhaust gas.

[0067] In another aspect of the present invention, there is also provided use of the catalyst composition, catalytic article, or layered catalytic article according to the present invention or the exhaust gas treatment system according to the present invention for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxide. EXAMPLES

[0068] The following examples are provided to further illustrate the embodiments of the present invention, but are not intended to limit the scope of the invention. While they are typical of those that might be used, other procedures, methodologies, or techniques known to those skilled in the art may alternatively be used.EXAMPLE 1 POWDER CATALYSTS

[0069] This example covers the preparation and composition of powder PGM catalysts with alumina and ceria-alumina composite supports. The compositions of the powder catalysts are listed in TABLE 1. All samples contained at least one ceria-alumina composite as a PGM support or an alumina as a reference PGM support.

[0070] In TABLE 1, the composition of each ceria-alumina composite support is represented by XCe-YAl, where X is weight percent of ceria in the composite and Y is the weight percent of alumina in the composite. For example, 20Ce-80Al denotes that a ceria-alumina composite contained 20 wt% CeO2and 80 wt% Al2O3. The number before each PGM denotes the metal content in a catalyst in weight percent. For example, 0.5Rh / 20Ce-80Al indicates that a catalyst contained 0.5 wt% Rh relative to the total weight of the catalyst (PGM + support), and that the support contained 20% ceria and 80% alumina. TABLE 1 Powder Sample Composition

[0071] Samples P1 to P4 were Rh catalysts supported on alumina and ceria-alumina composites with varying compositions. Sample P1 was a ceria-free Rh reference catalyst and was prepared by impregnating Rh nitrate solution on an alumina support to achieve a Rh loading of 0.5% by weight after calcination. The impregnated catalyst was dispersed in deionized water at about 30% solid content. An alumina-based binder (about 5 wt% of the catalyst) was added to the slurry. The resulting slurry was then dried at 100oC to obtained catalyst powder. The obtained powder was calcined at 550oC in air for 2 hours and then crashed and sieved to 250 – 500 ^m. The catalyst so obtained was designated as fresh catalyst. Samples P2, P3 and P4 were prepared using an identical method as Sample P1 but using 20Ce-80Al, 50Ce-50Al and 70Ce-30Al as Rh support, respectively.

[0072] Samples P5, P6 and P7 were Pt catalysts supported on alumina and ceria-alumina composites with varying compositions. Sample P5 was a ceria-free Pt reference catalyst prepared by impregnating a Pt tetraethanol amine hydroxide precursor on an alumina support followed by adding a nitrate acid solution (about 3 wt% of the support weight). The impregnated catalyst was dispersed in deionized water at about 30% solid content with pH adjusted to 4 – 4.5 using nitric acid. An alumina-based binder (about 5 wt% of the catalyst) was added to the slurry, and the resulting slurry was dried at 100oC to obtain catalyst powder. The obtained powder was calcined at 550oC in air for 2 hours and then crashed and sieved to 250 – 500 ^m. The catalyst so obtained was designated as fresh catalyst. Samples P6 and P7 were prepared using an identical method as Sample P5 but using 20Ce-80Al and 70Ce-30Al as Pt support, respectively. The Pt content of Samples P5, P6 and P7 was 2.0% by weight after calcination.

[0073] Samples P8 to P11 were Pd catalysts supported on alumina and ceria-alumina composites with varying compositions. P8 was a ceria-free Pd reference catalyst and prepared by impregnating Pd nitrate solution on an alumina support to achieve a Pd loading of 1.0 % by weight after calcination. The impregnated catalyst was dispersed in deionized water at about 30% solid content. An alumina-based binder (about 5 wt% of the catalyst) was added to the slurry. The resulting slurry was then dried at 100oC to obtain the powder catalyst. The obtained powder was calcined at 550oC in air for 2 hours, and then crashed and sieved to 250 – 500 ^m. The catalyst so obtained was designated as fresh catalyst. Samples P9, P10 and P11 were prepared using an identical method as Sample P8, except 20Ce-80Al, 30Ce-70Al and 50Ce- 50Al were used as Pd supports, respectively.

[0074] Samples P12, P13 and P14 are Pt-Rh bimetallic catalysts supported on alumina and ceria-alumina composites with varying compositions. P12, P13 and P14 were prepared by co- impregnating mixed solution of Pt nitrate and Rh nitrate on Al2O3, 20Ce-80Al and 70Ce-30Al, respectively. The impregnated catalyst was dispersed in deionized water at about 30% solid content. An alumina-based binder (about 5 wt% of the catalyst) was added to the slurry. The resulting slurry was then dried at 100oC to obtained catalyst powder. The obtained powder was calcined at 550oC in air for 2 hours and then crashed and sieved to 250 – 500 ^m. The catalyst so obtained was designated as fresh catalyst. Samples P12, P13 and P14 have an identical PGM loading: 1 wt% Pt and 0.5 wt% Rh.

[0075] Samples P15 to P19 were Rh catalysts with variable Rh loading and ceria-alumina composite supports with varying compositions. The mixture of supports included a ceria- alumina support and an oxygen storage component (OSC) at a weight ratio of 54 to 46. The OSC included of 40 wt% CeO2, 50 wt% ZrO2, 5 wt% La2O3and 5 wt% Pr6O11. Sample P15 to P18 were prepared by impregnating Rh solution on the ceria-alumina and OSC mixture containing 54 weight percent 8Ce-92Al and 46 weight percent OSC. The impregnated catalyst was dispersed in deionized water at about 30% solid content. An alumina-based binder (about 5 wt% of the catalyst) was added to the slurry. The resulting slurry was then dried at 100oC to obtain the catalyst powder. The resulting powder was calcined at 550oC in air for 2 hours and then crashed and sieved to 250 – 500 ^m. The catalyst so obtained was designated as fresh catalyst. Samples P15 to P18 contained 0.1%, 0.2%, 0.3% and 0.4% Rh by weight after calcination. Sample P19 was prepared in an identical method as Samples P15 to P19, except the support mixture contained 54% 70Ce-30Al and 46% OSC. Sample P19 has a Rh loading of 0.1% by weight.

[0076] Samples P20 to P23 were Pt-Rh bimetallic catalysts supported ceria-alumina composites with varying compositions. Sample P20 was prepared by co-impregnating the mixed solution of Pt nitrate and Rh nitrate on the ceria-alumina and OSC mixture containing 54 weight percent 8Ce-92Al and 46 weight percent OSC. The impregnated catalyst was dispersed in deionized water at about 30% solid content. An alumina-based binder (about 5 wt% of the catalyst) was added to the slurry. The resulting slurry was then dried at 100oC to obtain catalyst powder. The obtained powder was calcined at 550oC in air for 2 hours and then crashed and sieved to 250 – 500 ^m. The catalyst so obtained was designated as fresh catalyst, and contained 1 wt% Pt and 0.2 wt% Rh. Sample P21 was prepared with the same method as Sample 20 but contained 1 wt% Pt and 0.1 wt% Rh. Samples P22 and P23 shared the same PGM loading as Sample 21 and were prepared using the same method as Sample 21 but using different support mixtures. The support mixtures for Sample P22 and P23 were 20Ce-80Al + OSC (54 and 46 weight percent, respectively) and 70Ce-30Al + OSC (54 and 46 weight percent, respectively), respectively. EXAMPLE 2 MONOLITH CORE CATALYSTS

[0077] This example covers the preparation and composition three monolith core PGM catalysts. Each catalyst contained 50 g / ft3Pt supported on 1.5 g / in3support. The support materials were Al2O3, 20Ce-80Al and 70Ce-30Al for the three catalysts (denoted C-1, C-2 and C-3, respectively). An alumina-based binder (0.05 g / in3) was included in the washcoat of each catalyst.

[0078] All catalysts were prepared using the same procedure. Briefly, Pt tetraethanol amine hydroxide precursor was first impregnated on a support material to about 60% incipient wetness point. The powder was then impregnated with a nitric acid solution to reach 100% incipient wetness with a solution quantity equivalent to about 3 wt% of the support weight. The impregnated powder was then dispersed in deionized water to about 40% solid content with constant mixing using a shear mixer. An alumina-based binder was added to the slurry, and the slurry was milled using a continuous mill to obtain a particle size distribution of D90< 12 – 14. (90% particles had diameters of less than 12 – 14 ^m). The slurry pH was controlled to 4.5 to 5.0. Nitric acid solution was used to lower slurry pH to ≤ 5.0. The solid content of the slurry was reduced to about 28% using deionized water to reach the target washcoat loading. A cylindrical monolith core (1 in diameter and 3 in long, 600 cells / in2with 3.5 mil wall thickness)was immersed in the slurry and then pull from the slurry. An air knife with pressurized air flow was used to remove the excess slurry alternating from either end of the core sample. When the coated sample reached the estimated wet weight target, it was dried using a catalyst drier unit and then calcined in air at 550oC for 2 h. The compositions of the monolith core catalysts C- 1, C-2, and C-3 are summarized in TABLE 2. TABLE 2 Monolith Core Catalyst CompositionsEXAMPLE 3 FULLY FORMULATED FULL-SIZED CATALYST A

[0079] This example covers the preparation and composition of a fully formulated full-sized catalyst hereinafter referred to as “Catalyst A”. A schematic diagram of Catalyst A is provided in FIG. 8. This catalyst included a substrate 801, a bottom layer with an inlet zone 802 and an outlet zone 803, and a top layer 804. Specifically, catalyst A was a zoned bilayer Pt / Pd / Rh catalytic article with a PGM loading of 120 g / ft3(Pt / Pd / Rh = 58 / 58 / 4) coated onto a cylindrical monolith cordierite substrate having dimensions of 4.66” in diameter and 3.81” in length, a cell density of 800 cpsi, and a wall thickness of 3 mils. Inlet Zone of Bottom Layer

[0080] The inlet zone of the bottom layer covered 50% of the substrate length from an inlet to middle with a PGM loading of 104.4 g / ft3(Pt / Pd / Rh = 0 / 104.4 / 0). This zone was formed by coating a slurry containing about 19.1 wt.% alumina, 67.0 wt.% of the stabilized ceria-zirconia mixed oxide (OSC with ~ 40 wt.% ceria), barium acetate to yield 9.6 wt.% of BaO, colloidal alumina binder to yield 1.4 wt.% of Al2O3, and palladium nitrate to yield 2.89 wt.% of Pd onto the substrate. The washcoat loading of the inlet zone of the bottom layer was about 2.09 g / in3after calcination at 550°C for 1 hour in air. Outlet Zone of Bottom Layer

[0081] The outlet zone of the bottom layer covered 50% of the substrate length from outlet to middle with a PGM loading of 69.6 g / ft3(Pt / Pd / Rh = 58 / 11.6 / 0). 11.6 g / ft3of Pd in the form of palladium precursor solution was impregnated onto a stabilized ceria-zirconia mixed oxide (OSC with ~ 40 wt.% ceria), and 58 g / ft3of Pt in the form of platinum precursor solution was impregnated onto a ceria-alumina composite (Ce-Al (1) in FIG.8) with approximately 8 wt.% ceria. This zone was formed by coating a slurry containing about 19.1 wt.% of the ceria- alumina composite with approximately 8 wt.% ceria, 67.0 wt.% of the stabilized ceria-zirconia mixed oxide (OSC with ~ 40 wt.% ceria), barium acetate to yield 9.6 wt.% of BaO, a colloidal alumina binder to yield 2.4 wt.% of Al2O3, a platinum-amine complex to yield 1.61 wt.% of Pt, and palladium nitrate to yield 0.32 wt.% of Pd onto the substrate. The washcoat loading of the outlet zone of the bottom layer was about 2.09 g / in3after calcination at 550°C for 1 hour in air. Top Layer

[0082] The top layer covered 100% of the substrate length and had a PGM loading of 33 g / ft3(Pt / Pd / Rh = 29 / 0 / 4). This layer was formed by coating a slurry mixture containing about 85.0 wt.% of the ceria-alumina composite with ~8 wt.% ceria, 11.3 wt.% of a ceria-zirconia composite (binder) with approximately 50 wt.% ceria, a platinum-amine complex to yield 1.59 wt.% of Pt, and rhodium nitrate to yield 0.22 wt.% of Rh over the bottom layer. The washcoat loading of the top layer was about 1.06 g / in3after calcination at 550°C for 1 hour in air. EXAMPLE 4 FULLY FORMULATED FULL-SIZED CATALYST B

[0083] This example covers the preparation and composition of a fully formulated full-sized catalyst hereinafter referred to as “Catalyst B”. A schematic diagram of Catalyst B is provided in FIG.6. Catalyst B was a zoned bilayer Pt / Pd / Rh catalytic article with a PGM loading of 120 g / ft3(Pt / Pd / Rh = 58 / 58 / 4) coated onto a cylindrical monolith cordierite substrate having dimensions of 4.66” in diameter and 3.81” in length, a cell density of 800 cpsi, and a wall thickness of 3 mils. This catalyst included a substrate 601, a bottom layer with an inlet zone 602 and an outlet zone 603, and a top layer 604. Contrasting the outlet zone of Catalyst A, which contained a ceria-alumina composite with a 8:92 ceria to alumina weight ratio, the outlet zone in Catalyst B 603 included a ceria-alumina composite with a 7:3 ceria to alumina weight ratio.Inlet Zone of the Bottom Layer

[0084] The inlet zone of the bottom layer covered 50% of the substrate length from an inlet to middle with a PGM loading of 104.4 g / ft3(Pt / Pd / Rh = 0 / 104.4 / 0). This zone was formed by coating a slurry containing about 19.1 wt.% of the alumina, 67.0 wt.% of the stabilized ceria- zirconia mixed oxide (OSC with ~ 40 wt.% ceria), barium acetate to yield 9.6 wt.% of BaO, colloidal alumina binder to yield 1.4 wt.% of Al2O3, and palladium nitrate to yield 2.89 wt.% of Pd onto the substrate. The washcoat loading of the inlet zone of the bottom layer was about 2.09 g / in3after calcination at 550°C for 1 hour in air. Outlet Zone of the Bottom Layer

[0085] The outlet zone of the bottom layer covered 50% of the substrate length from outlet to middle with a PGM loading of 69.6 g / ft3(Pt / Pd / Rh = 58 / 11.6 / 0). 11.6 g / ft3of Pd in the form of palladium precursor solution was impregnated onto a stabilized ceria-zirconia mixed oxide (OSC with ~ 40 wt.% ceria), and 58 g / ft3of Pt in the form of platinum precursor solution was impregnated onto a ceria-alumina composite with approximately 70 wt.% ceria. This zone was formed by coating a slurry containing about 19.1 wt.% of the ceria-alumina composite with approximately 70 wt.% ceria, 67.0 wt.% of the stabilized ceria-zirconia mixed oxide (OSC with ~ 40 wt.% ceria), barium acetate to yield 9.6 wt.% of BaO, a colloidal alumina binder to yield 2.4 wt.% of Al2O3, a platinum-amine complex to yield 1.61 wt.% of Pt, and palladium nitrate to yield 0.32 wt.% of Pd onto the substrate. The washcoat loading of the outlet zone of the bottom layer was about 2.09 g / in3after calcination at 550°C for 1 hour in air. Top Layer

[0086] The top layer covered 100% of the substrate length with a PGM loading of 33 g / ft3(Pt / Pd / Rh = 29 / 0 / 4). This layer was formed by coating a slurry mixture containing about 85.0 wt.% of the ceria-alumina composite with ~8 wt.% ceria, 11.3 wt.% of a ceria-zirconia composite (binder) with approximately 50 wt.% ceria, a platinum-amine complex to yield 1.59 wt.% of Pt, and rhodium nitrate to yield 0.22 wt.% of Rh over the bottom layer. The washcoat loading of the top layer was about 1.06 g / in3after calcination at 550°C for 1 hour in air. EXAMPLE 5 FULLY FORMULATED FULL-SIZED CATALYST C

[0087] This example covers the preparation and composition of a fully formulated full-sized catalyst hereinafter referred to as “Catalyst C”. This catalyst was a single layer Pt / Rh catalytic article with a PGM loading of 12 g / ft3 (Pt / Pd / Rh = 10 / 0 / 2) coated onto a cylindrical monolithcordierite substrate having dimensions of 5.2” in diameter and 3.96” in length, a cell density of 400 cpsi, and a wall thickness of 6.5 mils.

[0088] Catalyst C was formed by coating a slurry containing about 50.8 wt.% of ceria- alumina composite with ~ 8 wt.% ceria, 43.5 wt.% of the stabilized ceria-zirconia mixed oxide (OSC with ~40 wt.% ceria), barium acetate to yield 3.6 wt.% of BaO, zirconium acetate to yield 1.1 wt.% of ZrO2, a colloidal alumina binder to yield 0.7 wt.% of Al2O3, a platinum- amine complex to yield 0.21 wt.% of Pt, and rhodium nitrate to yield 0.04 wt.% of Rh onto the substrate. The washcoat loading was about 2.76 g / in3 after calcination at 550 ºC for 1 hour in air. EXAMPLE 6 POWDER CATALYST AGING CONDITIONS AND EVALUATION PROCEDURES

[0089] This example summarizes the methods and conditions used to evaluate powder catalyst aging. Catalyst Aging Conditions

[0090] All catalysts were aged at 1050oC for 5 hrs. with 10% H2O under an alternating lean / rich feed (10 minutes 4% air / 10 minutes 4% H2 / N2). Catalyst Evaluation Procedures

[0091] The aged catalysts were evaluated in a powder reactor using a light-off protocol with a ^=1 oscillating feed ( ^=0.95 / 1.05 cycled at 1 Hz) from 175 to 450oC at a monolith equivalent GHSV of 70,000 h-1. For light-off tests, the lean feed ( ^=1.05) consists of 0.7% CO, 0.22% H2, 3000 ppm HC (C1) (propene: propane =2:1), 1500 ppm NO, 14% CO2, 10% H2O and ~1.8% O2. The rich feed ( ^=0.95) included 2.33% CO, 0.77% H2, 3000 ppm HC (C1), 1500 ppm NO, 14% CO2, 10% H2O and ~0.7% O2. The exact lambda values were fine-tuned by adjusting the O2level based on an upstream λ-sensor. The concentrations of carbon monoxide (CO), nitric oxide (NO) and hydrocarbons (HC) were continuously measured before and after catalysis. Conversion of CO, NO, and HC is calculated as the percent of disappearance of each species (i.e., Conversion = (Inlet concentration – Outlet concentration) / Inlet concentration x 100%). Catalyst activity was also characterized by catalyst light-off temperature, which is defined as the temperature required to achieve 50% conversion in a conversion – temperature plot, herein denoted as T50. Light-off temperatures for CO, NO and HC are expressed as CO T50, NO T50 and HC T50, respectively.

[0092] The performance evaluations were conducted with a sequence of four runs. The first run (Run 1) included a light-off test with ^=1 (0.95 / 1.05) feed. The second run (Run 2) included a light-off test with ^=1 (0.95 / 1.05) feed. The third run (Run 3) included a ^-sweep at 450oC (from ^=1.05 to ^=0.96). The fourth run (Run 4) included a Light-off test with ^=1 (0.95 / 1.05) feed. Run 1 was used for catalyst stabilization. Run 2 (second light-off) data were used for activity comparison. Run 3 exposed a catalyst to a rich environment ( ^=0.96) at the end of the test. Thus, Run 4 data were used to evaluate the effect of reduction by comparison with Run 2. EXAMPLE 7 MONOLITH CORE CATALYST AGING CONDITIONS AND EVALUATION PROCEDURES

[0093] This example overviews the methods and conditions used to evaluate monolith core catalyst aging. Catalyst Aging Conditions

[0094] Monolith core samples were aged in a tube reactor at 980oC for 5 h in a cyclic feed. The procedure consisted of three phases. The first phase involved ramping temperature from room temperature to 980oC under 10% H2O / N2flow. The second phase was performed at 980oC for 5 hours, and involved cycles with 1 min rich feed (5% H2 / N2, 10% H2O), 1 min lean feed (10% H2O / air) and 1 min stoichiometric feed (10% H2O / air). The third (“cool down”) phase lowered the temperature from 980oC to 200oC in 10% H2O / N2and from 200oC to room temperature in N2. Catalyst Evaluation Procedures

[0095] The aged monolith core catalysts were evaluated in a monolith core reactor at a gas hourly space velocity (GHSV) of 60,000 h-1with a constant ^=0.99 feed and a continuous temperature ramping from 150 to 500oC at a rate of 10oC / min. The feed consisted of 1.5% CO, 0.45% H2, 3000 ppm C1 HC (C3H6 / C3H8 = 2:1), 500 ppm NO, 14% CO2, 10% H2O, adjusted O2to ^=0.99. The concentrations of carbon monoxide (CO), nitric oxide (NO) and hydrocarbons (HC) were continuously measured before and after catalysts. CO, NO, and HC conversion were calculated as outlined in Example 6. Catalyst activity was also characterized by catalyst light-off temperature. Light-off temperature is denoted as T50. Light-off temperatures for CO, NO and HC are expressed as CO T50, NO T50 and HC T50, respectively.

[0096] The performance evaluations were conducted with a sequence of four runs. Runs 1, 2, and 4 utilized light-off tests with ^=0.99 (constant) feed. Run 3 utilized a ^-sweep at 450oC(from ^=1.05 to ^=0.96). Run was used as catalyst stabilization. Run 2 (second light-off) data were used for activity comparison. Run 3 exposed the catalysts to a rich environment ( ^=0.96) at the end of the test. Run 4 data were used to evaluate the effect of reduction treatment through comparison with Run 2. EXAMPLE 8 FULLY FORMULATED FULL-SIZED CATALYST AGING CONDITIONS AND EVALUATION PROCEDURES

[0097] This example summarizes the methods and conditions used to evaluate fully formulated catalyst aging. Catalyst Aging Conditions

[0098] Full-size catalysts were aged using a 4-mode exothermic aging protocol with effective catalyst temperature of 8770C for 60 hours with phosphorus doped fuel on an engine setup. Catalytic articles A and B were mounted on close coupled (CC) front location, while catalytic article C was mounted on close coupled rear location. The engine-out gas feed composition alternated between rich and lean to simulate typical vehicle operating conditions. Catalyst Evaluation Procedures

[0099] Emission performance was tested using a 2.0 L turbocharged ULEV70 vehicle with a close coupled (CC) + underfloor (UF) emissions control system configuration. Catalysts A and B were tested as CC catalyst, while catalyst C was used as a common UF catalyst. EXAMPLE 9 CO, NO, AND HC CONVERSION BY SUPPORTED PGM POWDER CATALYSTS

[0100] CO, NO, and HC conversion by powder catalysts P1-P23 were analyzed according to the procedures outlined in EXAMPLE 6.

[0101] FIGS. 1A-1C show conversion data for CO, NO, and HC, respectively, for supported Rh catalysts P1-P4 as a function of temperature. Catalysts P4 (0.5Rh / 70Ce-30Al) and P3 (0.5Rh / 50Ce-50Al) exhibited higher CO conversion activity than catalysts P2 (0.5Rh / 20Ce- 20Al) and P1 (0.5Rh / Al2O3). Catalyst P4 exhibited the highest NO and HC conversion activities. CO, NO, and HC T50 (oC) values during Runs 2 and 4 are summarized in TABLE 3.TABLE 3 Supported Rh Catalyst T50 Values for CO, NO, and HC

[0102] FIGS. 2A-2C show conversion data for CO, NO, and HC, respectively, for supported Pt catalysts P5-P7 as a function of temperature. Conversion efficiency correlated with ceria content for CO, NO, and HC, with P7 (2Pt / 70Ce-30Al) exhibiting the highest conversion efficiencies, P5 exhibiting the lowest conversion efficiencies (2Pt / Al2O3) and P6 (2Pt / 20Ce- 80Al) exhibiting intermediate conversion efficiencies. The T50 values of catalysts P5-P7 are shown in TABLE 4. Notably, the Run 2 T50 values of P7 were more than 90oC lower than the Run 2 T50s of P6. TABLE 4 Supported Pt Catalyst T50 Values for CO, NO, and HCaConversion did not reach 50% by 450oC (the highest tested temperature)

[0103] FIGS. 3A-3C show conversion data for CO, NO, and HC, respectively, for supported Pd catalysts P8-P11 as a function of temperature. As with the supported Pt catalysts, conversion efficiency correlated with ceria content for CO, NO, and HC, with P11 (1Pd / 50Ce-50Al) exhibiting the highest conversion efficiencies, followed by P10 (1Pd / 30Ce-70Al), P9 (1Pd / 20Ce-80Al), and P8 (1Pd / Al2O3). The T50 values of catalysts P8-P11 are shown in TABLE 5.TABLE 5 Supported Pd Catalyst T50 Values for CO, NO, and HC

[0104] TABLE 6 provides T50 values for supported Pt-Rh catalysts P12-P14, which contained 1% Pt and 0.5% Rh. P14 (1Pt-0.5Rh / 70Ce-30Al), which had the highest ceria content of the three supported Pt-Rh catalysts, exhibited the lowest T50 values. Notably, in Run 2 the T50 of P14 was lower than the T50 of P13 (1Pt-0.5Rh / 20Ce-80Al) by 40, 48 and 48oC for CO, NO and HC, respectively. In Run 4, the T50 of P14 was lower than P13 (1Pt-0.5Rh / 20Ce- 80Al) by 24, 26 and 24oC for CO, NO and HC, respectively. TABLE 6 Supported Pt-Rh Catalyst T50 Values for CO, NO, and HC

[0105] TABLE 7 provides T50 values for Rh catalysts with mixed supports that included ceria-alumina composites and oxygen storage components (OSCs). P19, which included a ceria-alumina composite with 70 weight percent ceria and 30 weight percent alumina, exhibited higher conversion activity than P15, which included the same Rh content but a lower proportion of ceria. The activity of P19 exhibited similar conversion activities as P16-P18, which included higher Rh content but lower ceria content.TABLE 7 Ceria-Alumina and OSC Supported Rh Catalyst T50 Values for CO, NO, and HC

[0106] TABLE 8 provides T50 values for Pt-Rh catalysts with mixed supports that included ceria-alumina composites and OSCs. For a same Rh loading, P23, which contained the highest ceria content, exhibited lower T50 values than P22 and P21. TABLE 8 Ceria-Alumina and OSC Supported Pt-Rh Catalyst T50 Values for CO, NO, and HCEXAMPLE 10 CO, NO, AND HC CONVERSION BY MONOLITH CORE CATALYSTS

[0107] CO, NO, and HC conversion by monolith core catalysts C1-C3 were analyzed according to the procedures outlined in EXAMPLE 7. FIGS. 4A-C show the conversions of CO, NO and HC (Run 2) over monolith core samples C1, C2 and C3 as a function of temperature. Table 9 lists the T50 values of Samples C1 to C3 for Run 2 and Run 4. Monolith core catalyst C3, which included the highest ceria content of the three catalysts, exhibitedsignificantly higher conversion activities (corresponding to lower T50s) than monolith core catalysts C2 and C1. TABLE 9 Monolith Core Catalyst T50 Values for CO, NO, and HCaConversion did not reach 50% by 500oC (the highest tested temperature). EXAMPLE 11 ENGINE RESULTS OF FULLY FORMULATED CATALYSTS

[0108] Emissions performance analyses were performed on fully formulated full-sized catalysts A+C and B+C according to the procedures outlined in EXAMPLE 8. The results of these analyses are summarized in FIG.5. Briefly, Catalysts B and C (tested as a pair) generated lower emissions than Catalysts A and C (tested as a pair) for both non-methane hydrocarbons (NMHCs) and NOx over the FTP test cycle. EXAMPLE 12 PHYSICAL PROPERTIES OF SUPPORT MATERIALS

[0109] This example covers BET surface areas of pure ceria and multiple ceria-alumina composites following calcination. In general, the BET surface area of a Ce-Al material decreases with increasing CeO2 content after 1000oC / 4 h calcination. For pure CeO2, despite its initial high surface area (150 m2 / g), the BET surface area was reduced to 24 m2 / g (by 84%) after calcination at 1000oC for 4 hours. For all Ce-Al materials, the surface area reduction following 4-hour 1000oC calcination was less than 50%. The specific surface areas measured by the BET method for three Ce-Al materials and pure CeO2 as a function of calcination temperature are shown in TABLE 10. TABLE 10 Specific Surface Areas (SSA) of CeO2 / Al2O3 Support Materials and Pure CeO2

[0110] Although the invention has been described with reference to the presently preferred embodiment, it should be understood that various modifications can be made without departing from the spirit of the invention. Accordingly, the invention is limited only by the following claims.

Claims

What Is Claimed Is:

1. A catalyst composition comprising: a) one or more platinum group metals (PGM) and b) a ceria-alumina composite comprising ceria and alumina in a weight ratio of between 1:1 and 19:1; wherein the one or more platinum group metals are supported on the ceria- alumina composite.

2. A catalyst composition according to claim 1, wherein the platinum group metal is platinum, rhodium or a combination thereof.

3. The catalyst composition of claim 1 or claim 2, wherein the catalyst composition does not comprise palladium.

4. The catalyst of any one of claims 1-3, wherein a weight ratio of ceria to alumina in the ceria-alumina composite is between 1:1 and 3:

1.

5. The catalyst composition of any one of claims 1-3, wherein a weight ratio of ceria to alumina in the ceria-alumina composite is between 13:7 to 3:

1.

6. The catalyst composition of any one of claims 1-5, further comprising an oxygen storage component.

7. The catalyst composition of claim 6, wherein the platinum group metal is supported on the oxygen storage component.

8. The catalyst composition of claim 6 or claim 7, wherein the oxygen storage component comprises Y2O3, Nd2O3, La2O3, Pr6O11, or a combination thereof.

9. The catalyst composition of any one of claims 6-8, wherein the oxygen storage component comprises between about 10 and 70 weight percent ceria.

10. The catalyst composition of any one of claims 1-9, wherein the platinum group metal is between about 0.025 and 5 weight percent (wt%) of the catalyst.

11. The catalyst of any one of claims 1-10, wherein the PGM is: i) rhodium present at about 0.05 to 1 weight percent of the catalyst composition; ii) platinum present at about 0.25 to 4 weight percent of the catalyst composition; iii) palladium present at about 0.25 to 4 weight percent of the catalyst composition; iv) platinum and palladium each present at about 0.25 to 2 weight percent of the catalyst composition; v) platinum present at about 0.25 to 2 weight percent of the catalyst and rhodium present at about 0.05 to 1 weight percent of the catalyst composition; vi) palladium present at about 0.25 to 2 weight percent of the catalyst and rhodium present at about 0.05 to 1 weight percent of the catalyst composition; or vii) platinum present at about 0.25 to 2 weight percent of the catalyst, palladium present at about 0.25 to 2 weight percent of the catalyst, and rhodium present at about 0.05 to 1 weight percent of the catalyst composition.

12. The catalyst composition of any one of claims 1-11, wherein the catalyst composition comprises between about 10% and 80% of the ceria-alumina composite by weight.

13. A catalytic article comprising the catalyst composition of any one of claims 1-12 disposed on a substrate.

14. A layered catalytic article comprising: a) a substrate, b) a first layer disposed on the substrate comprising the catalyst composition of any one of claims 1-12, and c) a second layer disposed on the first layer comprising a platinum group metal supported on a ceria-alumina composite.

15. The layered catalytic article of claim 14, wherein: i) the second layer further comprises an oxygen storage component,ii) the ceria-alumina composite of the second layer comprises less than 30% ceria by weight; iii) the platinum group metal of the second layer is platinum, rhodium, or a combination thereof; or iv) a combination thereof.

16. The layered catalytic article of claim 14 or claim 15, wherein the first layer comprises a second catalyst composition comprising a platinum group metal supported on an alumina component in a first zone and the catalyst composition of any one of claims 1-12 in a second zone.

17. The layered catalytic article of claim 16, wherein: i) the second catalyst composition further comprises an oxygen storage component, ii) the alumina component further comprises up to 20% ceria by weight.

18. The layered catalytic article of claim 16 or claim 17, wherein the first zone is an inlet zone and the second zone is an outlet zone.

19. The catalytic article of claim 13 or the layered catalytic article of any one of claims 14-18, wherein the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate and a woven fiber substrate.

20. An exhaust gas treatment system for internal combustion engines, said system comprising the catalytic composition of any one of claims 1-12, the catalytic article of claim 13, or the layered catalytic article of any one of claims 14-19.

21. A method of treating a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxide, the method comprising contacting said exhaust stream with the catalytic composition of any one of claims 1-12, the catalytic article of claim 13, or the layered catalytic article of any one of claims 14-19.

22. A method of reducing hydrocarbons, carbon monoxide, and nitrogen oxide levels in a gaseous exhaust stream, the method comprising contacting a gaseous exhaust stream with the catalytic composition of any one of claims 1-12, the catalytic article of claim 13, or the layered catalytic article of any one of claims 14-19 to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxide in the exhaust gas.

23. Use of the catalytic composition of any one of claims 1-12, the catalytic article of claim 13, or the layered catalytic article of any one of claims 14-19 for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxide.

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