Fuel cut NOx control TWC system

Abstract

The present disclosure relates to catalyst compositions, catalytic articles for purifying exhaust gas emissions, and methods of making and using the catalyst compositions and catalytic articles. In particular, the disclosure relates to catalysts having a catalytic material on a substrate, the catalytic material having a first layer and a second layer, where the first layer provides an effective lean NOx trap function and the second layer provides effective three-way conversion of carbon monoxide, hydrocarbons, and nitrogen oxides (NOx).

Description

[Technical Field]

[0001] FIELD OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to the field of three-way conversion catalysts and their use in exhaust gas treatment systems for reducing hydrocarbons, carbon monoxide and nitrogen oxides. [Background technology]

[0002] Background of the Invention Exhaust gas treatment for gasoline-powered vehicles is typically achieved using one or more three-way conversion (TWC) automotive catalysts. These three-way conversion automotive catalysts are effective at reducing nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) pollutants in engine exhaust. For example, a typical exhaust aftertreatment system for a gasoline engine consists of two TWC catalysts: a first / upstream TWC catalyst mounted near the exhaust manifold and engine compartment (close-coupled position, CC), and a second / downstream TWC catalyst located either immediately adjacent to the first TWC catalyst (second close-coupled position, CC2) or under the vehicle body (underfloor position, UF). TWC catalysts typically contain oxygen storage components (OSCs) and / or one or more platinum group metals (PGMs), such as platinum, palladium, and / or rhodium, supported on a refractory metal oxide support.

[0003] Modern gasoline engines are equipped with electronic fuel injection and air intake systems that deliver a constantly fluctuating mixture—one that oscillates rapidly and continuously between lean (low fuel / high air) and rich (high fuel / low air) exhaust. These oscillations occur at relatively low amplitudes near the stoichiometric air-fuel ratio, under the direction of a computer-aided engine control unit (ECU) and onboard lambda sensors, creating optimal reaction conditions for the TWC catalyst, resulting in near-complete simultaneous conversion of NOx, CO, and HC.

[0004] Driven by market demands and legislative requirements, improving fuel economy in internal combustion engines has become crucial. As a fuel-saving strategy, shutting off fuel injection during deceleration or high-speed cruising conditions has become increasingly common for gasoline engine calibrations. A typical fuel-cut event involves significantly reducing or even eliminating fuel injection, while maintaining a significant portion of the air intake. This operation creates a lean exhaust mixture, which oxidizes the TWC catalyst in the aftertreatment system. After fuel cut, NOx breakthrough from the TWC catalyst often occurs when the engine returns to a near-stoichiometric oscillation mode. This NOx slippage is due to delayed regeneration of active PGM components present in the TWC catalyst. In the face of increasingly stringent emissions regulations, there is a strong need for the continued development of improved TWC catalysts that can be used in gasoline engine exhaust aftertreatment systems, particularly those that can function effectively in conjunction with periodic fuel-cut events. Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure relates to catalytic materials with three-way conversion and NOx trapping capabilities (referred to as TWC / NT catalysts) and to catalyst composites comprising the TWC / NT catalyst for mitigating NOx breakthrough during fuel cut events. TWC / NT catalyst composites generally comprise catalytic materials with at least two layers: one layer effective for providing lean NOx trapping capabilities and one layer for effective conversion of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Such TWC / NT catalyst composites can be used in the exhaust treatment systems of gasoline engines, enabling fuel cut events that increase the thermal efficiency of the fuel. In certain embodiments, the TWC / NT catalyst compositions and related catalyst composites disclosed herein are effective in treating NOx slip typically associated with transitions between rich and lean engine conditions during fuel cut events. In some embodiments, the TWC / NT catalyst composition ("Inventive System: TWC + TWC / NT") achieves even lower NO tailpipe emissions compared to conventional TWC catalysts. [Means for solving the problem]

[0006] In one aspect, the present disclosure provides a layered catalyst composite having a catalytic material on a substrate, the catalytic material comprising: a first layer effective to provide lean NOx trap function, the layer comprising a platinum component, a first refractory metal oxide, and a NOx storage component selected from the group consisting of an alkaline earth metal oxide component, a rare earth metal oxide component, or a combination thereof; and a second layer effective to provide three-way conversion (TWC) of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), the second layer comprising a rhodium component, an oxygen storage component (OSC), and a second refractory metal oxide, the second layer having a loading of about 1 g / ft on the substrate. 3 ~approx. 50g / ft 3 In certain embodiments, the layered catalyst composite has a platinum group metal loading of about 2 g / ft 3 ~about 40g / ft 3 , or about 5 g / ft 3 ~about 30g / ft 3Also, in some embodiments, the layered catalyst composite has a loading of about 0.1 g / in on the substrate. 3 ~approx. 5.0g / in 3 is.

[0007] In another aspect, the present disclosure provides a layered catalyst composite having a catalytic material on a substrate, the catalytic material comprising: a first layer effective to provide lean NOx trap function, the layer comprising a platinum component, a first refractory metal oxide, and a NOx storage component selected from the group consisting of an alkaline earth metal oxide component, a rare earth metal oxide component, or a combination thereof; and a second layer effective to provide three-way conversion (TWC) of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), the second layer comprising a rhodium component, an oxygen storage component (OSC), and a second refractory metal oxide, the second layer having a loading of about 0.1 g / in on the substrate. 3 ~approx. 5.0g / in 3 In certain embodiments, the washcoat loading is about 1.0 g / in 3 ~approx. 4.5g / in 3 or approximately 2.0 g / in 3 ~Approx. 4.2g / in 3 is.

[0008] The composition of the first layer of the disclosed catalyst composite can vary. In some embodiments of the present disclosure, a platinum component is impregnated into a first refractory metal oxide, the refractory metal oxide impregnated with the platinum component comprising the platinum component in an amount of about 0.01% to about 10% by weight based on the refractory metal oxide. In some embodiments, the NOx storage component is selected from barium oxide, magnesium oxide, calcium oxide, strontium oxide, ceria, gadolinia, lanthana, neodymia, praseodymia, samaria, scandia, ytterbia, yttria, and combinations thereof. In some embodiments, the NOx storage component comprises an alkaline earth metal oxide component, and the first layer comprises the alkaline earth metal oxide component in an amount of about 1% to about 30% by weight.

[0009] In certain embodiments, the first layer comprises a platinum component impregnated into a first refractory metal oxide, where the first refractory metal oxide comprises alumina-ceria; and barium oxide. Also, in certain embodiments, the NOx storage component and the first refractory metal oxide are in the form of a premix comprising the NOx storage-refractory metal oxide. For example, in some embodiments, the NOx storage-refractory metal oxide is selected from barrier-alumina, barrier-ceria, barrier-alumina-ceria, and combinations thereof. Optionally, the first layer can further comprise a platinum group metal (PGM) component selected from palladium, rhodium, and combinations thereof.

[0010] The composition of the second layer of the catalytic composites disclosed herein can also be varied. In some embodiments, a rhodium component is impregnated into the OSC, and the rhodium-impregnated OSC comprises a rhodium component in an amount of about 0.01% to about 10% by weight, based on the weight of the OSC. In some embodiments, the OSC comprises ceria. For example, in certain embodiments, the OSC comprises ceria in an amount of about 1% to about 80% by weight, based on the weight of the OSC. In some embodiments, the OSC comprises ceria selected from the group consisting of zirconia (ZrO), hafnia (HfO), titania (TiO), praseodymia (PrO), and the like. 11 In certain embodiments, the second layer comprises ceria with rhodium (Y2O3), yttria (YO3), neodymia (Nd2O3), lanthana (La2O3), gadolinium oxide (Gd2O3), or combinations thereof. In certain embodiments, the second layer comprises a rhodium component impregnated in an OSC, where the OSC comprises ceria; and alumina. Optionally, the second layer can further comprise a PGM component selected from palladium, platinum, and combinations thereof.

[0011] In some embodiments, the catalytic material of the layered catalyst composite disclosed herein comprises platinum, palladium, and rhodium, wherein the platinum to rhodium weight ratio is in the range of 1 / 5 to 20 / 1, and the platinum to rhodium weight ratio is in the range of 1 / 2 to 20 / 1. The substrate of the disclosed layered catalyst composite, in some embodiments, is a wall-flow filter substrate or a flow-through substrate. In some embodiments, the first layer is disposed directly on the substrate, and the second layer is disposed on top of the first layer. In some embodiments, the second layer is disposed directly on the substrate, and the first layer is disposed on top of the second layer.

[0012] In another aspect, the present disclosure provides a method for reducing NOx levels in an exhaust gas stream during a fuel cut event, the method comprising contacting the exhaust gas stream with a layered catalyst composite disclosed herein for a time and at a temperature sufficient to reduce NOx levels. In an additional aspect, the present disclosure provides a method for reducing NO levels in tailpipe exhaust, the method comprising contacting the exhaust gas stream with a layered catalyst composite disclosed herein for a time and at a temperature sufficient to reduce NO levels in the tailpipe exhaust relative to a comparative TWC catalyst located further downstream.

[0013] The present disclosure also provides, in another aspect, an emissions treatment system comprising: an engine generating an exhaust gas stream; a TWC article disposed downstream of the engine and in fluid communication with the exhaust gas stream, the TWC article adapted for CO and HC reduction and NOx conversion to N2; and a layered catalyst composite disclosed herein disposed downstream of the TWC article. In some embodiments, the engine is a gasoline engine. The TWC article, in certain embodiments, is in a first close-coupled position and the layered catalyst composite is in a second close-coupled position or an underfloor position.

[0014] The present disclosure includes, but is not limited to, the following embodiments.

[0015] Embodiment 1: A layered catalyst composite having a catalytic material on a substrate, the catalytic material comprising: a first layer effective to provide lean NOx trap function, the layer comprising a platinum component, a first refractory metal oxide, and a NOx storage component selected from the group consisting of an alkaline earth metal oxide component, a rare earth metal oxide component, or a combination thereof; and a second layer effective to provide three-way conversion (TWC) of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), the layer comprising a rhodium component, an oxygen storage component (OSC), and a second refractory metal oxide, the layer having a loading of about 1 g / ft on the substrate. 3 ~approx. 50g / ft 3 A layered catalyst composite having a platinum group metal of

[0016] Embodiment 2: The loading is about 2 g / ft 3 ~about 40g / ft 3 3. The layered catalyst composite of any preceding embodiment, wherein

[0017] Embodiment 3: The loading is about 5 g / ft 3 ~about 30g / ft 3 3. The layered catalyst composite of any one of the preceding embodiments, wherein

[0018] Embodiment 4: A layered catalyst composite is formed on a substrate at a loading of about 0.1 g / in 3 ~approx. 5.0g / in 3 3. The layered catalyst composite of any one of the preceding embodiments, having a catalytic material of

[0019] Embodiment 5A: A layered catalyst composite having a catalytic material on a substrate, the catalytic material comprising: a first layer effective to provide lean NOx trap function, the layer comprising a platinum component, a first refractory metal oxide, and a NOx storage component selected from the group consisting of an alkaline earth metal oxide component, a rare earth metal oxide component, or a combination thereof; and a second layer effective to provide three-way conversion (TWC) of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), the layer comprising a rhodium component, an oxygen storage component (OSC), and a second refractory metal oxide, the layer comprising a rhodium component, an oxygen storage component (OSC), and a second refractory metal oxide, the catalytic material having a loading of about 0.1 g / in on the substrate.3 ~approx. 5.0g / in 3 A layered catalyst composite having a catalyst material of

[0020] Embodiment 6: The washcoat loading is about 1.0 g / in 3 ~approx. 4.5g / in 3 3. The layered catalyst composite of any one of the previous embodiments, wherein

[0021] Embodiment 7: The washcoat loading is about 2.0 g / in 3 ~Approx. 4.2g / in 3 3. The layered catalyst composite of any one of the preceding embodiments, wherein

[0022] Embodiment 8: The layered catalyst composite of any one of the preceding embodiments, wherein the platinum component is impregnated into a first refractory metal oxide, and the platinum component-impregnated refractory metal oxide comprises the platinum component in an amount of about 0.01% to about 10% by weight based on the refractory metal oxide.

[0023] Embodiment 9: The layered catalyst composite of any one of the previous embodiments, wherein the NOx storage component is selected from barium oxide, magnesium oxide, calcium oxide, strontium oxide, ceria, gadolinia, lanthana, neodymia, praseodymia, samaria, scandia, ytterbia, yttria, and combinations thereof.

[0024] Embodiment 10: The layered catalyst composite of any one of the preceding embodiments, wherein the NOx storage component comprises an alkaline earth metal oxide component, and the first layer comprises the alkaline earth metal oxide component in an amount between about 1% and about 30% by weight.

[0025] Embodiment 11: The layered catalyst composite of any one of the preceding embodiments, wherein the first layer comprises: a platinum component impregnated in a first refractory metal oxide, the first refractory metal oxide comprising alumina-ceria; and barium oxide.

[0026] Embodiment 12: The layered catalyst composite of any one of the preceding embodiments, wherein the NOx storage component and first refractory metal oxide are in the form of a premix comprising NOx storage-refractory metal oxide.

[0027] Embodiment 13: The layered catalyst composite of any one of the preceding embodiments, wherein the NOx storage-refractory metal oxide is selected from barrier-alumina, barrier-ceria, barrier-alumina-ceria, and combinations thereof.

[0028] Embodiment 14: The layered catalyst composite of any one of the preceding embodiments, wherein the first layer further comprises a platinum group metal (PGM) component selected from palladium, rhodium, and combinations thereof.

[0029] Embodiment 15: The layered catalyst composite of any one of the preceding embodiments, wherein the rhodium component is impregnated into an OSC, and the rhodium-impregnated OSC comprises the rhodium component in an amount from about 0.01% to about 10% by weight based on the metal oxide.

[0030] Embodiment 16: The layered catalyst composite of any one of the preceding embodiments, wherein the OSC comprises ceria.

[0031] Embodiment 17: The layered catalyst composite of any one of the preceding embodiments, wherein the OSC comprises ceria in an amount from about 1% to about 80% by weight, based on the weight of the OSC.

[0032] Embodiment 18: The OSC is selected from the group consisting of zirconia (ZrO), hafnia (HfO), titania (TiO), praseodymia (PrO 11 ), yttria (YO), neodymia (NdO), lanthana (LaO), gadolinium oxide (GdO), or combinations thereof.

[0033] Embodiment 19: The layered catalyst composite of any one of the preceding embodiments, wherein the second layer comprises a rhodium component impregnated in an OSC, the OSC comprising ceria; and alumina.

[0034] Embodiment 20: The layered catalyst composite of any one of the preceding embodiments, wherein the second layer further comprises a PGM component selected from palladium, platinum, and combinations thereof.

[0035] Embodiment 21: The layered catalyst composite of any one of the preceding embodiments, wherein the catalytic material comprises platinum, palladium, and rhodium, wherein the mass ratio of platinum to palladium is in the range of 1 / 5 to 20 / 1, and the mass ratio of platinum to rhodium is in the range of 1 / 2 to 20 / 1.

[0036] Embodiment 22: The layered catalyst composite of any one of the preceding embodiments, wherein the substrate is a wall-flow filter substrate or a flow-through substrate.

[0037] Embodiment 23: The layered catalyst composite of any one of the preceding embodiments, wherein the first layer is disposed directly on a substrate and the second layer is disposed on top of the first layer.

[0038] Embodiment 24: The layered catalyst composite of any one of the preceding embodiments, wherein the second layer is disposed directly on a substrate and the first layer is disposed on top of the second layer.

[0039] Embodiment 25: A method of reducing NOx levels in an exhaust gas stream during a fuel cut event, comprising contacting the exhaust gas stream with the layered catalyst composite of any one of the preceding embodiments for a time and at a temperature sufficient to reduce NOx levels in the exhaust gas stream.

[0040] Embodiment 26: A method of reducing NO levels in tailpipe exhaust, comprising contacting an exhaust gas stream with the layered catalyst composite of any one of the preceding embodiments for a time and at a temperature sufficient to reduce NO levels in the tailpipe exhaust relative to a comparative TWC catalyst located further downstream.

[0041] Embodiment 27: An emission treatment system comprising: an engine generating an exhaust gas stream; a TWC article disposed downstream of the engine and in fluid communication with the exhaust gas stream, the TWC article adapted for the reduction of CO and HC and the conversion of NOx to N2; and the layered catalyst composite of any one of the preceding embodiments disposed downstream of the TWC article.

[0042] Embodiment 28: The emission treatment system of any one of the preceding embodiments, wherein the engine is a gasoline engine.

[0043] Embodiment 29: The emission treatment system of any one of the preceding embodiments, wherein the TWC article is in a first proximal coupled position and the layered catalyst composite is in a second proximal coupled position or an underfloor position.

[0044] These and other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description read in conjunction with the accompanying drawings, which are briefly described below. The present disclosure encompasses any combination of two, three, four, or more features or elements described in this disclosure or claimed in one or more claims, whether such features or elements are expressly combined or described in a particular embodiment description or claim herein. The present disclosure is intended to be interpreted holistically, such that any separable features or elements disclosed in any of its aspects and embodiments should be considered as intended to be combinable unless the context clearly dictates otherwise. [Brief explanation of the drawings]

[0045] To aid in understanding embodiments of the present disclosure, reference is made to the accompanying drawings, which are not necessarily drawn to scale. Reference numerals indicate components of exemplary embodiments of the present disclosure. It should be noted that the drawings are illustrative only and should not be construed as limiting the present disclosure. [Figure 1] 1 is a perspective view of a honeycomb-type substrate that may be provided with a catalytic article according to the present disclosure. [Figure 2] Figure 2 is an enlarged partial cross-sectional view of Figure 1 taken along a plane parallel to the edge of the substrate carrier of Figure 1. Figure 2 shows an enlarged view of the multiple gas flow channels shown in Figure 1. In one embodiment, the substrate is a monolithic flow-through substrate. [Figure 3] 2 is a cutaway view of a cross section enlarged relative to FIG. 1, in which the honeycomb substrate of FIG. 1 represents a wall-flow filter substrate monolith. [Figure 4] 1 is a cross-sectional view of an embodiment of a zoned or area-divided catalyst article with overlapping layers. [Figure 5] 3 is a cross-sectional view of another embodiment of a zoned catalyst article in which the layers overlap. [Figure 6] 1 is a cross-sectional view of an embodiment of a zoned catalyst article in which the layers do not overlap. [Figure 7] 1 is a cross-sectional view of one embodiment of a layered catalyst article. [Figure 8] FIG. 2 is a cross-sectional view of an embodiment of another layered catalyst article. [Figure 9] FIG. 1 illustrates an embodiment of an engine processing system. [Figure 10] 1 is a line graph showing cumulative tailpipe NOx emissions traces for a catalyst system of the present invention and a comparative catalyst system with a TWC-NT catalyst article. [Figure 11]1 is a line graph showing tailpipe NOx emissions traces for a catalyst system of the present invention and a comparative catalyst system with a TWC / NT catalyst article during a 475 second period in FTP-75 with two representative fuel cut events. DETAILED DESCRIPTION OF THE INVENTION

[0046] Detailed Description of the Invention The present invention is described in detail below. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used in this specification and claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0047] The term "catalyst" or "catalyst composition," as used herein, refers to a material that promotes a reaction.

[0048] The terms "upstream" and "downstream," as used herein, refer to relative directions relative to the flow of engine exhaust gas stream from the engine toward the tailpipe, with the engine being in the upstream position and the tailpipe and any pollution abatement articles (such as catalysts and filters) being downstream from the engine.

[0049] The term "stream," as used herein, refers broadly to a combination of flowing gases that may include solid or liquid particulate matter. The term "gas stream" or "exhaust gas stream" refers to a flow of gaseous components, such as the exhaust of a combustion engine, that may entrain non-gaseous components, such as liquid droplets, solid particulates, etc. The exhaust gas stream of a combustion engine typically further includes products of combustion (CO and HO), products of incomplete combustion (carbon monoxide (CO) and hydrocarbons (HC)), oxides of nitrogen (NOx), combustible and / or carbonaceous particulate matter (soot), and unreacted oxygen and nitrogen.

[0050] The term "substrate," as used herein, refers to a monolithic material onto which the catalyst composition is disposed.

[0051] The term "support," as used herein, refers to a high surface area material, usually a metal oxide material, onto which the catalytic noble metal is applied.

[0052] The term "washcoat," as used herein, has its ordinary meaning in the art, i.e., a thin, adherent coating of catalytic or other material applied to a substrate material, such as a honeycomb-type carrier member, having sufficient porosity to allow the passage of a gas stream being processed. Washcoats are formed by preparing a slurry containing particles of a particular solids content (e.g., 10% to 60% by weight) in a liquid vehicle, which is then coated onto the substrate and dried to provide the washcoat layer.

[0053] The term "catalytic article," as used herein, refers to an element used to promote a desired reaction. For example, a catalytic article may include a washcoat containing a catalyst composition on a substrate.

[0054] "Impregnated" or "impregnation," as used herein, refers to the penetration of a catalytic material into the porous structure of a support material.

[0055] The term "reduction" means a decrease in quantity caused by any means.

[0056] catalyst materials The catalytic material of the present disclosure includes two catalyst compositions that can be arranged on a substrate in a layered configuration to form a TWC / NT catalyst composite. One layer of the catalytic material contains a first catalyst composition that provides lean NOx trapping functionality, and one layer contains a second catalyst composition suitable for achieving three-way conversion (TWC) of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). As described in more detail below, these layers can be arranged on the substrate in various configurations. Each catalyst composition is described in more detail below.

[0057] First Catalyst Composition The first catalyst composition includes a NOx storage component and at least one PGM component impregnated into a refractory metal oxide material. As used herein, "platinum group metal" or "PGM" refers to platinum group metals or their oxides, including platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), iridium (Ir), and combinations thereof. In some embodiments, the PGM component is platinum. In some embodiments, the PGM component is a combination of platinum and palladium. In a non-limiting example, platinum and palladium can be combined in a weight ratio of about 1:10 to about 10:0.1, or more preferably, about 1:1 to about 10:1. The concentration of the PGM component (e.g., Pd alone or in combination with Pd) can vary but is typically about 0.01% to about 10% by weight based on the weight of the impregnated refractory metal oxide material. Here, the total impregnated refractory metal oxide material includes the PGM component and the refractory metal oxide material. The amount of impregnated refractory metal oxide material in the first composition can vary, but is typically from about 10% to about 90%, from about 10% to about 80%, from about 10% to about 70%, from about 10% to about 60%, or from about 10% to about 50% by weight, based on the weight of the first catalyst composition.

[0058] As used herein, "refractory metal oxide" refers to a metal-containing oxide support that exhibits chemical and physical stability at elevated temperatures, such as those associated with the exhaust of gasoline and diesel engines. Exemplary refractory metal oxides include alumina, silica, zirconia, titania, ceria, and physical mixtures or chemical combinations thereof, including atomically doped combinations. In some embodiments, the refractory metal oxide may include, in addition to the aforementioned oxides, metal oxide(s) of alkali metals, metalloids, and / or transition metals, such as La, Mg, Ba, Sr, Zr, Ti, Si, Ce, Mn, Nd, Pr, Sm, Nb, W, Mo, Fe, or combinations thereof. In some embodiments, the amount of metal oxide in the refractory metal oxide material may vary from about 0.5% to about 70% by weight, based on the total weight of the refractory metal oxide material. Examples of metal oxide combinations include alumina-zirconia, ceria-zirconia, alumina-ceria-zirconia, lanthana-alumina, lanthana-zirconia, lanthana-zirconia-alumina, baria-alumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, and alumina-ceria.

[0059] In some embodiments, a high surface area, refractory metal oxide support is used, such as an alumina support material, also known as "gamma alumina" or "activated alumina," which is typically 60 m 2 / g, and in many cases, approximately 200m 2 / g or greater. "BET surface area" has its ordinary meaning, as determined by the Brunauer, Emmett, and Teller method of determining surface area by N2 adsorption. In one or more embodiments, the BET surface area is about 100 to about 150 m 2 / g range. Useful commercially available aluminas include high surface area aluminas, such as high bulk density gamma-alumina, and low or medium bulk density large pore gamma-alumina. In some embodiments, the PGM components are impregnated into a single refractory metal oxide material. For example, in some embodiments, the PGM components are impregnated into an alumina-ceria composite. In some embodiments, two or more PGM components may be impregnated into the same refractory metal oxide material. For example, in some embodiments, the palladium component and the platinum component may be impregnated into the same refractory metal oxide (e.g., ceria-alumina). Also, in some embodiments, the PGM components may be impregnated into two or more refractory metal oxides. In some embodiments, the two or more PGM components may be impregnated into different refractory metal oxide materials.

[0060] The NOx storage component may include an alkaline earth metal oxide component, a rare earth metal oxide component, or a combination thereof. For example, in some embodiments, the NOx storage component includes an alkaline earth metal oxide component. In some embodiments, the alkaline earth metal oxide component is selected from barium oxide, magnesium oxide, calcium oxide, strontium oxide, ceria, gadolinia, lanthana, neodymia, praseodymia, samaria, scandia, ytterbia, yttria, and combinations thereof. The NOx storage component is typically an essentially basic material that can form the corresponding carbonate upon contact with carbon dioxide (CO) from the air or exhaust mixture. In some embodiments, the NOx storage component includes a rare earth metal oxide component. The rare earth metal oxide component, in some embodiments, is selected from ceria, dysprosia, erbia, europia, gadolinia, holmia, lanthana, lutetia, neodymia, praseodymia, promethia, samaria, scandia, terbia, thulia, ytterbia, yttria, and combinations thereof. The amount of NOx storage component present in the first catalyst composition can vary, but is typically from about 1 to about 30%, from about 1 to about 20%, or from about 1 to about 10%, based on the weight of the first catalyst composition. In some embodiments, the NOx storage component may be physically mixed with one or more PGM-impregnated refractory metal oxide support materials in the first catalyst composition.

[0061] Second Catalyst Composition The second catalyst composition includes an OSC component, a refractory metal oxide material, and at least one PGM component, as defined herein. In some embodiments, the PGM component is rhodium. In some embodiments, the PGM component is a combination of rhodium and palladium. In such embodiments, the rhodium and palladium may be combined in a weight ratio of Rh:Pd of, for example, about 0.1:10 to about 10:0.1. In some embodiments, the PGM component further includes platinum. The concentration of the PGM component (e.g., Rh alone or in combination with Pd) can vary but is typically about 0.01% to about 10% by weight, based on the weight of the impregnated refractory metal oxide material. Here, the impregnated refractory metal oxide material includes the PGM component and the refractory metal oxide material.

[0062] In some embodiments, the PGM components are impregnated into a single refractory metal oxide material. For example, in some embodiments, the PGM components are impregnated into alumina. In some embodiments, two or more PGM components may be impregnated into the same refractory metal oxide material. For example, in some embodiments, a palladium component and a rhodium component may be impregnated into the same refractory metal oxide material (e.g., alumina). In some embodiments, two or more PGM components may be impregnated into different refractory metal oxide materials. The amount of PGM component-impregnated refractory metal oxide material in the second catalyst composition can vary, but is typically about 10% to about 90%, about 10% to about 80%, about 10% to about 70%, about 10% to about 60%, or about 10% to about 50%, by weight, based on the weight of the second catalyst composition.

[0063] As used herein, "OSC" refers to an oxygen storage component that exhibits oxygen storage capacity, often having multiple oxidation states and capable of actively reacting with oxidizing agents such as oxygen (O) or nitric oxide (NO) under oxidizing conditions, or with reducing agents such as carbon monoxide (CO), hydrocarbons (HC), or hydrogen (H) under reducing conditions. Specific examples of OSCs are rare earth metal oxides, which refer to one or more oxides of the scandium, yttrium, and lanthanum series as defined in the periodic table of the elements. Specific examples of suitable oxygen storage components include ceria and praseodymia, and combinations thereof.

[0064] In some embodiments, the OSC in the second catalyst composition is a catalyst that converts Ce to Cr under lean exhaust gas conditions where an excess amount of oxygen is present in the exhaust stream. 4+ and in the presence of rich exhaust gas conditions. 3+ This includes ceria in a form that releases oxygen when reduced to an oxidized state. Ceria can also be used as an oxygen storage component in combination with other materials, such as zirconium (Zr), hafnium (Hf), titanium (Ti), lanthanum (La), praseodymium (Pr), neodymium (Nd), niobium (Nb), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), osmium (Os), ruthenium (Ru), tantalum (Ta), zirconium (Zr), yttrium (Y), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), silver (Ag), gold (Au), samarium (Sm), gadolinium (Gd), and combinations comprising at least one of the foregoing metals. Various oxides (e.g., metals combined with oxygen (O)) can also be used. These include, for example, zirconia (ZrO2), hafnia (HfO2), titania (TiO2), praseodymia (Pr6O 11 ), yttria (Y2O3), neodymia (Nd2O3), lanthana (La2O3), gadolinium oxide (Gd2O3), or a mixture containing at least one of the foregoing.

[0065] The amount of ceria in the ceria-containing OSC can vary, but is typically from about 1% to about 80%, from about 5% to about 60%, from about 5% to about 40%, from about 5% to about 30%, or from about 10% to about 25% by weight, based on the weight of the OSC.

[0066] In some embodiments, the PGM component is impregnated into an OSC component, a refractory metal oxide material, or a combination thereof. For example, in some embodiments, the PGM component is impregnated into a ceria-zirconia-based OSC component. In some embodiments, two or more PGM components are impregnated into an OSC component, a refractory metal oxide material, or a combination thereof. For example, in some embodiments, a palladium component and a rhodium component are impregnated into the same ceria-zirconia-based OSC component. The amount of PGM component-impregnated OSC component in the second catalyst composition can vary, but is typically about 10% to about 90%, about 10% to about 80%, about 10% to about 70%, about 10% to about 60%, or about 10% to about 50%, by weight, based on the weight of the second catalyst composition.

[0067] catalyst article In accordance with one or more embodiments, the disclosed catalytic materials are typically disposed on a substrate. The substrate can be constructed of any material commonly used in manufacturing automotive catalysts, and typically comprises a metallic or ceramic monolithic honeycomb structure. The substrate typically comprises multiple walls for application and attachment of a washcoat containing the catalytic composition described herein, thereby acting as a carrier for the catalyst composition.

[0068] Exemplary metallic substrates include heat-resistant metals and metal alloys, such as titanium and stainless steel, as well as other alloys in which iron is a substantial or major component. Such alloys can include one or more of nickel, chromium, and / or aluminum. The total amount of these metals can advantageously constitute at least 15% by weight of the alloy, for example, 10-25% by weight chromium, 3-8% by weight aluminum, and up to 20% by weight nickel. The alloy can also contain small or trace amounts of one or more other metals, such as manganese, copper, vanadium, titanium, etc. The surface of the metal substrate can be oxidized at high temperatures, for example, above 1000°C, to form an oxide layer on the surface of the substrate, which can improve the corrosion resistance of the alloy and promote adhesion of a washcoat layer to the metal surface. Ceramic materials used to construct the substrate include suitable heat-resistant materials such as cordierite, mullite, cordierite-alpha alumina, silicon nitride, zircon-mullite, spodumene, alumina-silica magnesia, zirconium silicate, sillimanite, magnesium silicate, zircon, petalite, alpha-alumina, and aluminosilicates.

[0069] Any suitable substrate can be used, such as a monolithic flow-through substrate having a plurality of fine, parallel gas passages extending from the inlet to the outlet face of the substrate such that the passages accommodate fluid flow. The passages are essentially straight paths from the inlet to the outlet and are defined by walls onto which a catalytic material is applied as a washcoat. As a result, gas flowing along the passages comes into contact with the catalytic material. The flow passages in the monolithic substrate are thin-walled channels that can have any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, or circular. The structures can have from about 60 to about 1200 or more gas inlet openings (i.e., "cells") per square inch of cross section (cpsi), more commonly about 300-600 cpsi. The wall thickness of the flow-through substrate can vary, typically ranging from 0.002 to 0.1 inches. Typical commercially available flow-through substrates are cordierite substrates with 400 cpsi and a 6 mil wall thickness, or 600 cpsi and a 4 mil wall thickness. However, it is understood that the present invention is not limited to any particular substrate type, material, or geometric configuration.

[0070] In another embodiment, the substrate may be a wall-flow substrate, with each passageway plugged at one end of the substrate body by a nonporous plug, with alternate passageways plugged at both ends. This allows gas flow through the porous walls of the wall-flow substrate to reach the outlet. Such monolithic substrates can have a pressure of up to about 700 cpsi or more, e.g., about 100 to 400 cpsi, more typically about 200 to about 300 cpsi. The cross-sectional shape of each cell may vary as described above. Wall-flow substrates typically have a wall thickness of 0.002 to 0.1 inches. Typical commercially available wall-flow substrates are constructed of porous cordierite, with examples having a wall thickness of 10 mils at 200 cpsi or 8 mils at 300 cpsi, and wall porosity of 45 to 65%. Other ceramic materials, such as aluminum-titanate, silicon carbide, and silicon nitride, can also be used as wall-flow filter substrates. However, it is understood that the present disclosure is not limited to any particular substrate type, material, or geometry. It should be noted that if the substrate is a wall-flow substrate, the catalyst composition may penetrate into the pore structure of the porous walls (i.e., partially or completely block the pore openings) in addition to being disposed on the surface of the walls.

[0071] 1 and 2 illustrate an exemplary substrate 2 in the form of a flow-through substrate coated with a washcoat composition described herein. With reference to FIG. 1, the exemplary substrate 2 is cylindrical in shape and has a cylindrical outer surface 4, an upstream end surface 6, and a corresponding downstream end surface 8. The downstream end surface is identical to end surface 6. The substrate 2 has a plurality of fine, parallel gas flow passages 10 formed therein. As can be seen in FIG. 2, each passage 10 is defined by respective walls 12 and extends through the substrate 2 from the upstream end surface 6 to the downstream end surface 8, and each passage 10 is unobstructed so that a fluid flow, e.g., a gas flow, can flow longitudinally through the substrate 2 via the gas passage 10. As can be more easily seen in FIG. 2, each wall 12 is sized and configured so that the gas passage 10 has a substantially regular polygonal shape. As shown, the washcoat composition can be applied in multiple, separate layers, if desired. In the illustrated embodiment, the washcoat comprises a first separate washcoat layer 14 attached to the wall 12 of the substrate member and a second separate washcoat layer 16 applied over the surface of the first washcoat layer 14. The invention can be practiced with one or more (e.g., two, three, or four) washcoat layers. Although two layers are shown, the invention is not limited to this embodiment.

[0072] For example, in one embodiment, the catalyst article contains a catalyst material having multiple layers, each layer having a different composition. For example, in some embodiments, a first layer (e.g., layer 14 of FIG. 2) comprises a first catalyst composition as disclosed herein, and a second layer (e.g., layer 16 of FIG. 2) comprises a second catalyst composition as disclosed herein. In other embodiments, a first layer (e.g., layer 14 of FIG. 2) comprises a second catalyst composition as disclosed herein, and a second layer (e.g., layer 16 of FIG. 2) comprises a first catalyst composition as disclosed herein.

[0073] FIG. 3 illustrates an exemplary substrate 2 in the form of a wall-flow filter substrate coated with a washcoat composition described herein. As shown in FIG. 3, the exemplary substrate 2 has a plurality of passages 52. These passages are tubularly surrounded by the filter substrate's interior wall 53. The substrate has an inlet end 54 and an outlet end 56. The passages are alternately blocked at the inlet end by inlet plugs 58 and at the outlet end by outlet plugs 60, forming an opposing checkerboard pattern at the inlets 54 and outlets 56. Gas flow 62 enters through unblocked channel inlets 64, is stopped by outlet plugs 60, and diffuses through the (porous) channel wall 53 to the outlet side 66. The gas is prevented from returning to the inlet side of the wall by the presence of inlet plugs 58. The porous wall-flow filters used in this disclosure function as catalysts by including one or more catalytic materials on or within the walls of the element. The catalytic material may be present only on the inlet side of the element's wall, only on the outlet side, on both the inlet and outlet sides, or the wall itself may consist entirely or partially of catalytic material. The present invention encompasses the use of one or more layers of catalytic material on the inlet and / or outlet walls of the element.

[0074] In some embodiments, the catalytic material disposed on the substrate comprises multiple axial zone regions, each zone region having a different composition. For example, in some embodiments, two separate washcoat compositions can be coated onto the substrate in an axially zoned or zoned configuration. In some embodiments, the same substrate can be coated once with one washcoat composition and a second time with a different washcoat composition, where each washcoat composition is different. For example, in some embodiments, the two separate washcoat compositions can comprise separate catalyst compositions (i.e., a first catalyst composition and a second catalyst composition). In one embodiment, the first catalyst composition can be coated first from the inlet end of the filter, and the second catalyst composition can be coated second from the outlet end of the filter.

[0075] Examples of zoned substrates coated with washcoat compositions, such as the zoned substrates described above, are shown in Figures 4-8, where a first washcoat composition (e.g., a first catalyst composition) is applied to the inlet end to provide washcoat coverage of less than 95% of the filter length, and a second washcoat composition (e.g., a second catalyst composition) is applied to the outlet end to provide washcoat coverage of less than 95% of the filter length. For example, referring to Figure 4, substrate 22 has inlet end 25, outlet end 27, and an axial length extending between inlet end 25 and outlet end 27, and includes two distinct washcoat zones (regions). First washcoat zone 24 and second washcoat zone 26 are provided on substrate 22. First washcoat zone 24 extends from inlet end 25 and includes a first catalyst composition, and second washcoat zone 26 extends from outlet end 27 and includes a second catalyst composition. In some embodiments, the first washcoat zone 24 comprises the second catalyst composition, and the second washcoat zone 26 comprises the first catalyst composition. In some embodiments, the first washcoat zone 24 comprises the first catalyst composition, and the second washcoat zone 26 comprises the second catalyst composition. In certain embodiments, the first washcoat zone 24 extends from the front or inlet end 25 of the substrate 22 over a range of about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the length of the substrate 22. The second washcoat zone 26 extends from the rear outlet end 27 of the substrate over a range of about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the total axial length of the substrate 22. In the embodiment shown in FIG. 4, the second washcoat zone 26 at least partially overlaps the first washcoat zone 24 .

[0076] In another embodiment, as shown in FIG. 5 , a first washcoat zone (region) 24 extends from an inlet end 25 toward an outlet end 27. A second washcoat zone 26 is disposed adjacent to and downstream from the first washcoat zone 24. The first washcoat zone 24 at least partially overlaps the second washcoat zone 26. In one embodiment, the first washcoat zone 24 includes a first catalyst composition, and the second washcoat zone 26 includes a second catalyst composition. In some embodiments, the first washcoat zone 24 includes a second catalyst composition, and the second washcoat zone 26 includes the first catalyst composition. In certain embodiments, the first washcoat zone 24 extends from the forward end, i.e., inlet end 25, over a range of about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the length of the substrate 22. The second washcoat zone 26 extends from the rearward exit end 27 of the substrate 22 for about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the total axial length of the substrate 22.

[0077] In another embodiment, two washcoat slurries can be coated onto the same substrate in two separate zones, as shown in Figure 6. A first washcoat zone 24 includes a washcoat of a first catalyst composition, and a second washcoat zone 26 includes a washcoat of a second catalyst composition. These zones are arranged side-by-side along the length of the substrate 22 with no overlap between the zones. In some embodiments, the first washcoat zone 24 includes a second catalyst composition, and the second washcoat zone 26 includes the first catalyst composition. In some embodiments, the first washcoat zone 24 includes the first catalyst composition, and the second washcoat zone 26 includes the second catalyst composition. In certain embodiments, the first washcoat zone 24 extends from the front or inlet end 25 of the substrate 22 over a range from about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the length of the substrate 22. The second washcoat layer 26 extends from the rearward exit end 27 of the substrate 22 for about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the total axial length of the substrate 22.

[0078] 7, a first washcoat zone 24 is coated on the substrate 22, extending from the leading or inlet end 25 of the substrate 22 to the trailing or outlet end 27 of the substrate 22, and a second washcoat zone 26 is coated on the first washcoat 24 adjacent the leading or inlet end 25 of the substrate 22. The second washcoat zone extends only a portion of the length of the substrate 22 (i.e., terminates before reaching the trailing or outlet end 27 of the substrate 22). Also, in some embodiments, the first washcoat zone 24 comprises a second catalyst composition and the second washcoat zone 26 comprises the first catalyst composition. In some embodiments, the first washcoat zone 24 comprises the first catalyst composition and the second washcoat zone 26 comprises the second catalyst composition. In certain embodiments, the second washcoat zone 26 extends from the forward inlet end 25 of the substrate 22 to about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the total axial length of the substrate 22. The second washcoat layer 26 extends from the aft outlet end 27 of the substrate 22 to about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the total axial length of the substrate 22.

[0079] In another embodiment, as shown in FIG. 8 , a first washcoat zone 24 may be coated on the substrate 22 proximate the rear or outlet end 25 of the substrate 22 and extending only partially along the length of the substrate 22 (i.e., terminating before reaching the front or inlet end 25 of the substrate 22). The substrate 22 may also be coated with a second washcoat zone 26. In some embodiments, the first washcoat zone 24 includes a second catalyst composition, and the second washcoat zone 26 includes a first catalyst composition. In some embodiments, the first washcoat zone 24 includes a first catalyst composition, and the second washcoat zone 26 includes a second catalyst composition. As can be seen in FIG. 8 , the second washcoat zone 26 extends from the front or inlet end 25 of the substrate 22 to the rear or outlet end 27 of the substrate 22 (thus completely covering the entire surface of the first washcoat zone 26). In certain embodiments, the second washcoat zone 24 extends from the rearward exit end 27 of the substrate 22 for about 5% to about 95%, about 5% to about 75%, about 5% to about 50%, or about 10% to about 35% of the total axial length of the substrate 22.

[0080] In describing the amount of washcoat or catalytic metal component or other component of the composition, it is convenient to use the mass units of the component per unit volume of catalytic substrate. Thus, the units used herein are grams per cubic inch ("g / in"). 3 ") and grams per cubic foot ("g / ft 3 The unit of mass per volume, such as g / L, is used to refer to the mass of a component per volume of substrate, including the volume of voids in the substrate. Other units of mass per volume, such as g / L, may also be used. The total loading of catalytic materials (i.e., the platinum component impregnated in the refractory metal oxide material, the rhodium component impregnated in the second refractory metal oxide material, and, optionally, one or more PGM components impregnated in one or more supports) on the catalytic substrate is typically from about 1.0 to about 5.0 g / in for the entire catalyst article. 3 , more typically about 1.0 to about 4.5 g / in 3, or about 2.0 to about 4.2 g / in 3 The total loading of active metals (i.e., PGM components) without support material is typically from about 1 to about 50 g / ft for the entire catalyst article. 3 , about 2~40g / ft 3 , or about 5 to about 30 g / ft 3 It should be noted that these masses per unit volume are typically calculated by weighing the catalytic substrate before and after treatment with the corresponding catalytic washcoat composition, and that since the treatment process involves drying the catalytic substrate and calcining it at high temperatures, these masses represent essentially solvent-free catalytic coatings, since essentially all of the water in the washcoat slurry has been removed.

[0081] Methods for preparing the first and second catalyst compositions The support material impregnated with at least one PGM component present in the first and second layers of the disclosed catalytic composites is typically prepared by impregnating the support material in particulate form with an active metal solution, such as a platinum and / or rhodium and / or palladium precursor solution, using an incipient wetness technique.

[0082] The incipient wetness method, also known as capillary impregnation or dry impregnation, is commonly used to synthesize heterogeneous materials, i.e., heterogeneous catalysts. Typically, metal precursors are dissolved in an aqueous or organic solution, and the metal-containing solution is then added to a catalyst support. The catalyst support has a pore volume equal to the volume of the added solution. Capillary action draws the solution into the pores of the support. Adding more solution than the pore volume of the support changes the solution transport from a capillary action process to a much slower diffusion process. The catalyst can then be dried and calcined to remove volatile components in the solution and deposit the metal on the surface of the catalyst support. The concentration profile of the impregnated material depends on the mass transport conditions within the pores during impregnation and drying.

[0083] For example, in some embodiments, a platinum component-impregnated support material (present in a first catalyst composition of the disclosed catalyst composite) is prepared by impregnating a support material in particulate form (e.g., a refractory metal oxide and / or OSC) with a platinum precursor solution. In some embodiments, a rhodium component-impregnated support material (present in a second catalyst composition of the disclosed catalyst composite) is prepared by impregnating another support material in particulate form (e.g., a refractory metal oxide and / or OSC) with a rhodium precursor solution. In some embodiments, the active metals (e.g., platinum and / or rhodium) may be impregnated into separate support particles.

[0084] In some embodiments, the first and / or second catalyst compositions have multiple PGM components impregnated onto a support material. For example, the first and / or second catalyst compositions of the catalyst composite can further have a palladium component impregnated onto a support material and can be prepared by impregnating a particulate support material with a palladium precursor solution. The support material can be the same as or different from the support material of the platinum component-impregnated support material (present in the first catalyst composition of the disclosed catalyst composite) and / or the rhodium component-impregnated support material (present in the second catalyst composition of the disclosed catalyst composite). In some embodiments, two different PGM precursor solutions can be impregnated onto the support material simultaneously or sequentially.

[0085] The support particles are typically sufficiently dry to absorb substantially all of the solution and form a wet solid. An aqueous solution of a water-soluble compound or complex of the active metal is usually utilized. For example, rhodium chloride, rhodium nitrate (e.g., Rh(NO)3 and its salts), rhodium acetate, or combinations thereof in which rhodium is the active metal; platinum nitrate, platinum tetraamine complex, platinum acetate, or combinations thereof in which platinum is the active metal; and palladium chloride, palladium tetraamine complex, palladium acetate, or combinations thereof in which palladium is the active metal.

[0086] After treating the support particles with the active metal solution, the particles are dried, for example, by heat treating the particles at an elevated temperature (e.g., 100°C to 150°C) for a period of time (e.g., about 10 minutes to about 3 hours), and then calcined to convert the active metal to a more catalytically active form. An exemplary calcination process involves heat treating in air at a temperature of about 400°C to 600°C for 10 minutes to 3 hours. The above process can be repeated as necessary to achieve the desired level of active metal impregnation.

[0087] In some embodiments, at least one PGM component-impregnated support material is mixed with other components of the composition, as disclosed in detail above. For example, in some embodiments, a platinum component-impregnated support material is mixed with a NOx storage component (e.g., an alkaline earth metal component such as barium oxide) and / or a palladium component-impregnated support material to provide a first catalyst composition of the disclosed catalyst composite. In another example, a rhodium component-impregnated OSC is mixed with a refractory material and / or a palladium component-impregnated refractory support material to provide a second catalyst composition of the disclosed layered catalyst composite.

[0088] Substrate Coating Method The catalyst composition is typically prepared in the form of catalyst particles. These catalyst particles can be mixed with water to form a slurry for coating onto a catalyst substrate, such as a honeycomb-type substrate. In addition to the catalyst particles, the slurry can optionally contain a binder in the form of alumina, silica, zirconium acetate, colloidal zirconia, or zirconium hydroxide, an associative thickener, and / or a surfactant (including anionic, cationic, nonionic, or amphoteric surfactants). Other examples of binders include boehmite, gamma-alumina, or delta / theta-alumina, as well as silica sol. When present, the binder is typically used in an amount of about 1 to 10 wt. % of the total washcoat loading. Acidic or basic species can be added to the slurry to adjust the pH accordingly. For example, in some embodiments, the pH of the slurry is adjusted by adding ammonium hydroxide, aqueous nitric acid, or acetic acid. The typical pH range for the slurry is about 3 to 12.

[0089] The slurry can be milled to reduce particle size and promote particle mixing. This milling can be performed in a ball mill, continuous mill, or other similar equipment, and the solids content of the slurry can be, for example, about 20-60% by weight, more specifically, about 20-40% by weight. In one embodiment, the milled slurry is characterized by a D90 particle size of about 10 to about 40 microns, preferably 10 to about 30 microns, and more preferably about 10 to about 20 microns. D90 is determined using a specialized particle size analyzer. The equipment used in this example uses laser diffraction to measure particle size in a small amount of slurry. D90, typically in microns, means that 90% of the particles, by number, have a diameter smaller than that value.

[0090] The slurry is coated onto the catalyst substrate using washcoating techniques known in the art. In one embodiment, the catalyst substrate is dipped or otherwise coated with the slurry one or more times. The coated substrate is then dried at an elevated temperature (e.g., 100-150°C) for a period of time (e.g., 10 minutes to 3 hours) and then calcined, for example, by heating at 400-600°C, typically for about 10 minutes to about 3 hours. After drying and calcination, the final washcoat coating layer can be considered essentially solvent-free.

[0091] After calcination, the catalyst loading achievable by the washcoating technique described above can be determined by calculating the difference between the mass of the coated and uncoated substrate. As will be apparent to those skilled in the art, catalyst loading can be modified by altering the rheology of the slurry. Furthermore, the coating / drying / calcining process to produce a washcoat can be repeated as necessary to build the coating to a desired loading level or thickness. This means that multiple washcoats can be applied. The catalyst composition can be applied in multiple layers, each of which can have a different composition as described above (e.g., layers 14 and 16 in Figure 2).

[0092] Hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO x ) conversion method Generally, hydrocarbons, carbon monoxide, and nitrogen oxides present in the exhaust gas stream of a gasoline or diesel engine can be converted to carbon dioxide, nitrogen, oxygen, and water according to the equations shown below.

[0093] 2CO+O2→2CO2 C x H y +(x+y / 2)O2 → xCO2 + yH2O 2NO+2CO→N2+2CO2 2NO+2H2→N2+2H2O NO+C x H y →N2+H2O+CO2

[0094] Typically, hydrocarbons present in engine exhaust streams include C1-C6 hydrocarbons (ie, lower hydrocarbons), although higher hydrocarbons (greater than C6) can also be detected.

[0095] Aspects of the present disclosure relate to methods for at least partially converting HC, CO, and NOx in an exhaust gas stream during a fuel cut event, the method comprising contacting the exhaust gas stream with a catalytic article described herein for a time and at a temperature sufficient to reduce the levels of NOx and / or CO and / or HC. In some embodiments, the catalytic article converts hydrocarbons to carbon dioxide and water. In some embodiments, the catalytic article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of hydrocarbons present in the exhaust gas stream before contacting the catalytic article. In some embodiments, the catalytic article converts carbon monoxide to carbon dioxide. In some embodiments, the catalytic article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of carbon monoxide present in the exhaust gas stream before contacting the catalytic article. In some embodiments, the catalytic article converts nitrogen oxides to nitrogen. In some embodiments, the catalytic article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of nitrogen oxides present in the exhaust gas stream prior to contact with the catalytic article. In some embodiments, the catalytic article converts at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or at least about 95% of the total amount of hydrocarbons, carbon dioxide, and nitrogen oxides present in the exhaust gas stream prior to contact with the catalytic article.

[0096] Another aspect of the present disclosure relates to a method for at least partially capturing NOx using a lean NOx trap. The LNT catalyst operates under cyclic lean (trapping mode) and rich (regeneration mode) exhaust conditions, such as may occur during a fuel cut event, where NO converts to N2, as described below.

[0097] Lean condition: 2NO+O2→2NO2 (Trapping mode) 4NO2 + 2MCO3 + O2 → 2M(NO3)2 + 2CO2 Rich condition: M(NO3)2+2CO→MCO3+NO2+NO+CO2 (Regeneration mode) NO2+CO→NO+CO2 2NO+2CO→N2+2CO2 2NO+2H2→N2+2H2O

[0098] LNT applications are typically used to adsorb hydrocarbons (HC) from engine exhaust during vehicle start-up when the catalyst is too cold to oxidize the hydrocarbons to CO2 (cold start). When the exhaust temperature rises to a point where the platinum group metals in the catalyst become active, the hydrocarbons are released from the molecular sieve and subsequently oxidized to CO2. However, LNT systems can also be used to store and release NOx during fuel cut events.

[0099] Engine Processing System The present disclosure provides emissions treatment systems incorporating the TWC / NT catalyst composites described herein, for example, emissions treatment systems generally having an engine producing an exhaust gas stream and a catalytic article of the present invention disposed downstream of the engine and in fluid communication with the exhaust gas stream, which can be a gasoline engine.

[0100] In some embodiments, the emissions treatment system further includes one or more additional catalytic components. The relative arrangement of the various catalytic components present in the emissions treatment system can vary. For example, the treatment system can include additional components such as one or more additional three-way conversion (TWC) catalysts, hydrocarbon traps, ammonia oxidation (AMOx) materials, ammonia-producing catalysts, selective catalytic reduction (SCR) catalysts, NOx storage and / or trapping components (LNTs), and any combination thereof. Typically, systems including the TWC / NT catalyst composites disclosed herein include one or more TWC catalysts. The one or more TWC catalysts are not limited in composition and can include any TWC catalyst composition known in the art to be suitable for TWC activity. The above list of components is merely exemplary and should not be construed as limiting the scope of the present invention.

[0101] 9, an engine exhaust system according to one or more embodiments can include a three-way conversion (TWC) catalyst 720 downstream from the engine and upstream of a TWC / NT catalyst composite 730 disclosed herein. Exhaust gas from a gasoline engine 710 travels through exhaust conduit 715 to the TWC catalyst 720 and then through conduit 725 to the TWC / NT catalyst composite 730 described herein. In one or more embodiments, the engine exhaust system 700 further includes an optional catalyst 740 (e.g., an SCR catalyst, an ammonia oxidation catalyst, etc.) located downstream of the TWC / NT catalyst composite 730 via exhaust conduit 735.

[0102] In one or more embodiments, an engine exhaust system includes a TWC catalyst mounted near the engine (e.g., a close-coupled location, CC) and a TWC / NT catalyst article according to the present disclosure mounted either immediately adjacent to the TWC catalyst (a second close-coupled location, CC2) or under the vehicle body (an underfloor location, UF).

[0103] Table 1 illustrates various non-limiting exhaust gas treatment system configurations according to one or more embodiments, where each catalyst is connected to the next catalyst via an exhaust conduit, with the engine being upstream of catalyst A, which is upstream of catalyst B, which is upstream of catalyst C.

[0104] [Table 1]

[0105] Each catalyst article, for example, the catalyst articles shown in the system configurations in Table 1, can comprise a wall-flow filter or a flow-through filter, as disclosed above. Note that in one or more embodiments, the TWC and TWC / NT are all disposed on a flow-through filter substrate. Also, in some embodiments, one of the catalyst articles in the system comprises a wall-flow filter substrate. For example, in some embodiments, the TWC / NT catalyst composite of the present invention can be the catalytic material mounted on a wall-flow filter substrate. [Example]

[0106] Aspects of the present disclosure are further described by way of the following examples, which are provided to illustrate certain aspects of the invention and should not be construed as limiting the invention.

[0107] [Table 2]

[0108] Example 1 In this example, a two-layer washcoat structure with a PGM loading of 150 g / ft 3 The preparation of a universal upstream TWC catalyst (Pt / Pd / Rh=0 / 136.6 / 13.4) is described.

[0109] Bottom Layer: The components present in the bottom layer were 4% lanthana-stabilized gamma-alumina, ceria (approximately 40% ceria and zirconia composite), barium oxide, lanthanum oxide, neodymium oxide, and palladium, with concentrations of 29.3%, 56.4%, 6.8%, 1.6%, 2.3%, and 3.6%, respectively, based on the fired weight of the bottom washcoat. The stabilized alumina and ceria-zirconia composite were mixed with deionized water to form a slurry. The other components, including promoters and stabilizers, were introduced as their corresponding soluble salts. Palladium (136.6 g / ft 3 ) in the form of a palladium nitrate solution was slowly added dropwise to the slurry while stirring. The pH of the slurry was adjusted to 3.5-4.5 with dilute nitric acid solution. The slurry was milled to reduce particle size and then milled to a concentration of 2.21 g / in 3 The catalyst was coated onto a 4.66" x 2.87" cylindrical monolith substrate with a cell density of 600 cpsi (cells per square inch) and a wall thickness of 3.5 mil (approximately 100 μm) at a washcoat loading of 1000 sq. ft. After coating, the catalyst was calcined in air at 550°C for 1 hour.

[0110] Top Layer: The components present in the top layer were 20% zirconia and 3% lanthana-doped gamma-alumina, ceria (approximately 40% ceria-zirconia composite), barium oxide, zirconium oxide, and rhodium, with concentrations of 64.0%, 30.1%, 3.9%, 1.3%, and 0.7%, respectively, based on the calcined weight of the bottom washcoat. The doped alumina and ceria-zirconia composite were mixed with deionized water to form a slurry. Other components, including promoters and stabilizers, were introduced as their corresponding soluble salts. The rhodium (13.4 g / ft 3 ) in the form of a rhodium nitrate solution was slowly added dropwise to the slurry with stirring. The pH of the slurry was adjusted to 4.0-4.5 with dilute nitric acid solution. The slurry was milled to reduce particle size and then milled to a concentration of 1.16 g / in 3 After coating, the catalyst was calcined in air at 550° C. for 1 hour.

[0111] Comparative Example 2 In this example, a two-layer washcoat structure with a PGM loading of 20g / ft 3 The preparation of a reference downstream TWC catalyst (Pt / Pd / Rh=0 / 16 / 4) is described.

[0112] Bottom Layer: The components present in the bottom layer were refractory gamma-alumina, ceria, approximately 30% ceria and zirconia composite, barium oxide, lanthanum oxide, zirconium oxide, and palladium, with concentrations of 21.0%, 70.4%, 4.9%, 0.9%, 2.4%, and 0.4%, respectively, based on the calcined weight of the bottom washcoat. The alumina and ceria-zirconia composite were mixed with deionized water to form a slurry. The other components, including promoters and stabilizers, were introduced as their corresponding soluble salts. Palladium (16 g / ft 3 ) was in the form of a palladium nitrate solution, which was slowly added dropwise to the slurry with stirring. The pH of the slurry was adjusted to about 3.5-4.5 with acetic acid. The slurry was milled to reduce particle size and then milled to a concentration of 2.06 g / in 3 The catalyst was coated onto a 4.66" x 3.58" cylindrical monolith substrate with a cell density of 600 cpsi (cells per square inch) and a wall thickness of 3.5 mil (approximately 100 μm) at a washcoat loading of 1000 sq. ft. After coating, the catalyst was calcined in air at 550°C for 1 hour.

[0113] Top Layer: The components present in the top layer were refractory gamma-alumina, ceria (approximately 10% ceria and zirconia composite), barium oxide, zirconium oxide, and rhodium, with concentrations of 31.2%, 62.4%, 3.1%, 3.1%, and 0.15%, respectively, based on the fired weight of the bottom washcoat. Rhodium (4 g / ft 3) was impregnated into the ceria-zirconia composite in the form of a rhodium nitrate solution to form a wet powder using the incipient wetness technique. Alumina and the rhodium-impregnated ceria-zirconia composite were mixed with deionized water to form a slurry. Other ingredients, including promoters and stabilizers, were introduced as their corresponding soluble salts. The pH of the slurry was adjusted to 4.0-4.5 with acetic acid. The slurry was milled to reduce particle size and then milled to a concentration of 1.60 g / in. 3 After coating, the catalyst was calcined in air at 550° C. for 1 hour.

[0114] Example 3 In this example, a two-layer washcoat structure with a PGM loading of 20g / ft 3 The preparation of a (Pt / Pd / Rh=12 / 4 / 4) TWC / NT catalyst is described.

[0115] Bottom layer: The components present in the bottom layer are 20% barrier-doped alumina, high surface area cerium oxide (BET surface area: 180 m 2 / g), magnesium oxide, zirconium oxide, platinum, and palladium, whose concentrations were 53.0%, 35.4%, 3.8%, 0.29%, and 0.03%, respectively, based on the calcined weight of the bottom washcoat. 3 ) and palladium (1.2g / ft 3 ) in the form of an aqueous platinum-amine complex solution and an aqueous palladium nitrate solution, respectively, were sequentially impregnated into the barrier-ceria-alumina composite to form a wet powder at the incipient wetness point. The impregnated composite was mixed with deionized water to form a slurry. Other components, including promoters and stabilizers, were introduced as their corresponding soluble salts. The pH of the slurry was adjusted to about 5.5-6.5 with acetic acid. The slurry was milled to reduce particle size and then mixed at a concentration of 2.40 g / in 3The catalyst was coated onto a 4.66" x 3.58" cylindrical monolith substrate with a cell density of 600 cpsi (cells per square inch) and a wall thickness of 3.5 mil (approximately 100 μm) at a washcoat loading of 1000 sq. ft. After coating, the catalyst was calcined in air at 550°C for 1 hour.

[0116] Top Layer: The components present in the top layer were 4% lanthana-stabilized gamma-alumina, ceria (approximately 22% ceria and zirconia composite), barium oxide, zirconium oxide, palladium, and rhodium at concentrations of 30.4%, 60.8%, 6.1%, 2.4%, 0.10%, and 0.14%, respectively, based on the calcined weight of the bottom washcoat. Palladium (2.8 g / ft 3 ) was impregnated onto the stabilized alumina in the form of a palladium nitrate solution to form a wet powder at the incipient wetness point. 3 ) was impregnated onto the ceria-zirconia composite in the form of a rhodium nitrate solution. The rhodium-impregnated ceria-zirconia composite alumina and palladium-impregnated alumina were mixed with deionized water to form a slurry. Other components, including promoters and stabilizers, were introduced as their corresponding soluble salts. The pH of the slurry was adjusted to 4.0-4.5 with acetic acid. The slurry was milled to reduce particle size and then milled to a concentration of 1.64 g / in. 3 After coating, the catalyst was calcined in air at 550° C. for 1 hour.

[0117] Example 4 In this example, a two-layer washcoat structure with a PGM loading of 20g / ft 3 The preparation of a (Pt / Pd / Rh=12 / 4 / 4) TWC / NT catalyst is described.

[0118] Bottom layer: The components present in the bottom layer were a composite of 10% baria-doped ceria and alumina (1:1 mass ratio), magnesium oxide, zirconium oxide, platinum, and palladium, with concentrations of 88.4%, 7.5%, 3.8%, 0.29%, and 0.03%, respectively, based on the calcined mass of the bottom washcoat. Platinum (12 g / ft 3 ) and palladium (1.2g / ft 3 ) were sequentially impregnated onto the barrier-ceria-alumina composite in the form of an aqueous platinum-amine complex solution and an aqueous palladium nitrate solution, respectively, to form a wet powder at the incipient wetness point. The impregnated composite was mixed with deionized water to form a slurry. Other components, including promoters and stabilizers, were introduced as their corresponding soluble salts. The pH of the slurry was adjusted to about 5.5-6.5 with acetic acid. The slurry was milled to reduce particle size, and then 2.40 g / in 3 The catalyst was coated onto a 4.66" x 3.58" cylindrical monolith substrate with a cell density of 600 cpsi (cells per square inch) and a wall thickness of 3.5 mil (approximately 100 μm) at a washcoat loading of 1000 sq. ft. After coating, the catalyst was calcined in air at 550°C for 1 hour.

[0119] Top layer: The top layer was coated with the same ingredients and procedure as in Example 3.

[0120] Example 5 In this example, a two-layer washcoat structure with a PGM loading of 10g / ft 3 The preparation of a TWC / NT catalyst with a Pt / Pd / Rh ratio of 5 / 1 / 4 is described. The bottom layer is 5 g / ft. 3 of platinum and 1g / ft 3 of palladium, with the top layer containing 4g / ft 3 This example was carried out following the same procedure as Example 4, except that it contained 0.05% Rh.

[0121] Example 6: Testing Full-size monolith catalysts were mounted in steel converter cans and aged in the exhaust line of a gasoline engine operating on a fuel-cut aging cycle. The upstream TWC catalyst (Example 1) was aged for 50 hours at a maximum bed temperature of 950°C. The downstream catalysts were aged for 50 hours at a maximum bed temperature of 935°C for CC1+CC2 applications (Table 2, Systems 1-4) or at a maximum bed temperature of 910°C for CC+UF applications (Table 2, Systems 5 and 6). The aged catalysts were tested in a 1.8-liter SULEV-30 gasoline test vehicle operating on the USFTP-75 driving cycle according to approved procedures and tolerances. The particular FTP-75 test used in this study included approximately 42 fuel-cut events during vehicle deceleration or cruising operations.

[0122] The tailpipe bag emissions in the FTP-75 test are summarized in Table 2. In the CC1+CC2 catalyst configuration, Comparative Example 2 (TWC, 20 g / ft 3 The baseline system 1, using PGM, Pt / Pd / Rh=0 / 16 / 4, produced 8.9 mg / mile of NOx at the tailpipe. 3 Systems 2 and 3 with PGM, Pt / Pd / Rh (12 / 4 / 4) reduced tailpipe NOx emissions to 4.8-5.6 mg / mile. This represents a 37-46% reduction in NOx emissions. The inventive system had comparable tailpipe NMHC performance but moderately superior CO performance compared to the baseline system. Modal data for cumulative tailpipe NOx emissions for the baseline and inventive systems are shown in Figure 10 and are in good agreement with the bag data discussed above. Figure 11 plots a representative range of NOx concentration traces (in ppm) as a function of test time (in seconds), clearly demonstrating the occurrence of a NOx benefit or effect during a fuel cut event. System 4 used Example 4 (10 g / ft ) as the CC2 catalyst. 3PGM, Pt / Pd / Rh=5 / 1 / 4) was employed, but this catalyst is the TWC / NT catalyst of the present invention with 50% less PGM relative to Comparative Example 1. The NOx benefit remains significant for System 4, demonstrating the potential for TWC / NT catalysts to realize cost savings.

[0123] In the CC+UF catalyst configuration, baseline System 5, using Comparative Example 2 as the UF catalyst, produced 11.2 mg / mile of NOx at the tailpipe. In contrast, inventive System 6, using TWC / NT Example 4 as the UF catalyst, reduced tailpipe NOx emissions to 7.4 mg / mile. Furthermore, the TWC / NT catalyst significantly exceeded the traditional TWC effect on CO emissions.

[0124] References throughout this specification to "one embodiment," "a particular embodiment," "one or more embodiments," or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. Thus, the use of the phrases "in one or more embodiments," "in a particular embodiment," "in one embodiment," or "in an embodiment" in various places throughout this specification do not necessarily refer to the same embodiment of the present invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0125] Although the present invention has been described herein with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present invention without departing from the spirit and scope of the invention. Therefore, it is intended that the present invention cover all such modifications and variations as come within the scope of the appended claims and their equivalents. [Explanation of symbols]

[0126] 2 Base material 4 External surface 6 Upstream end face 8 Downstream end face 10 Gas flow path 12 Wall 14 First washcoat layer 16 Second washcoat layer 22 Base material 24 First Wash Coat Zone 25 Inlet end 26 Second Wash Coat Zone 27 Outlet end 52 Passage 53 Channel Wall 54 Inlet end 56 Outlet end 58 Inlet plug 60 outlet plug 62 Gas Flow 64 Channel Entrance 66 Exit side 710 gasoline engine 715 Exhaust duct 720 Three-Way Conversion (TWC) Catalyst 725 Conduit 730 TWC / NT catalyst composite 735 Exhaust duct 740 Optional catalyst

Claims

1. A layered catalyst composite having a catalyst material on a substrate, the catalyst material comprising a first layer effective to provide lean NOx trap function, the layer including a platinum component, a first refractory metal oxide, and a NOx storage component selected from the group consisting of an alkaline earth metal oxide component, a rare earth metal oxide component, or a combination thereof; and a second layer effective to provide three-way conversion (TWC) of carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOx), the second layer comprising a rhodium component, an oxygen storage component (OSC), and a second refractory metal oxide; Equipped with Loading on substrate is approximately 1 g / ft ３ ~ about 50g / ft ３ a platinum group metal of the first layer comprising a platinum component impregnated in the first refractory metal oxide comprising alumina-ceria, and barium oxide; A layered catalyst composite comprising:

2. The loading is about 2 g / ft ３ ~About 40g / ft ３ 2. The layered catalyst composite of claim 1, wherein:

3. The loading is about 5 g / ft ３ ~Approx. 30g / ft ３ 2. The layered catalyst composite of claim 1, wherein:

4. The layered catalyst composite is deposited on the substrate at a loading of about 0.1 g / in ３ ~ about 5.0 g / in ３ 4. The layered catalyst composite according to claim 1, wherein the catalyst material is:

5. A layered catalyst composite having a catalyst material on a substrate, the catalyst material comprising a first layer effective to provide lean NOx trap function, the layer including a platinum component, a first refractory metal oxide, and a NOx storage component selected from the group consisting of an alkaline earth metal oxide component, a rare earth metal oxide component, or a combination thereof; and a second layer effective to provide three-way conversion (TWC) of carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOx), the second layer comprising a rhodium component, an oxygen storage component (OSC), and a second refractory metal oxide; Equipped with Loading on substrate is approximately 0.1 g / in ３ ~ about 5.0 g / in ３ a catalyst material of Loading on substrate is approximately 1 g / ft ３ ~ about 50g / ft ３ a platinum group metal of the first layer comprising a platinum component impregnated in the first refractory metal oxide comprising alumina-ceria, and barium oxide; A layered catalyst composite comprising:

6. The layered catalyst composite is deposited on a substrate at a loading of about 1.0 g / in ３ ~ about 4.5 g / in ３ 6. The layered catalyst composite of claim 5, having a catalytic material of 7. The layered catalyst composite is formed on a substrate at a loading of about 2.0 g / in ３ ~Approx. 4.2g / in ３ 6. The layered catalyst composite of claim 5, having a catalytic material of

8. 10. The layered catalyst composite of claim 1, wherein the platinum component is impregnated into a first refractory metal oxide, and the platinum component-impregnated refractory metal oxide comprises the platinum component in an amount of from about 0.01% to about 10% by weight based on the refractory metal oxide.

9. 9. The layered catalyst composite of claim 1, wherein the NOx storage component is selected from barium oxide, magnesium oxide, calcium oxide, strontium oxide, ceria, gadolinia, lanthana, neodymia, praseodymia, samaria, scandia, ytterbia, yttria, and combinations thereof.

10. 10. The layered catalyst composite of claim 1, wherein the NOx storage component comprises an alkaline earth metal oxide component, and the first layer comprises the alkaline earth metal oxide component in an amount of from about 1 wt. % to about 30 wt. %.

11. 11. The layered catalyst composite of any one of claims 1 to 10, wherein the NOx storage component and first refractory metal oxide are in the form of a NOx storage-refractory metal oxide comprising premix.

12. 12. The layered catalyst composite of claim 11, wherein the NOx storage-refractory metal oxide is selected from barrier-alumina, barrier-ceria, barrier-alumina-ceria, and combinations thereof.

13. 13. The layered catalyst composite of any one of claims 1 to 12, wherein the first layer further comprises a platinum group metal (PGM) component selected from palladium, rhodium, and combinations thereof.

14. 14. The layered catalyst composite of any one of claims 1 to 13, wherein the rhodium component is impregnated into an OSC, and the rhodium-impregnated OSC comprises the rhodium component in an amount of from about 0.01% to about 10% by weight based on the metal oxide.

15. 15. The layered catalyst composite of any one of claims 1 to 14, wherein the OSC comprises ceria.

16. 16. The layered catalyst composite of any one of claims 1 to 15, wherein the OSC comprises ceria in an amount of from about 1% to about 80% by weight based on the weight of the OSC.

17. The OSC is zirconia (ZrO ２ ), hafnia (HfO ２ ), titania (TiO ２ ), praseodymia (Pr ６ O １１ ), yttria (Y ２ O ３ ), neodymia (Nd ２ O ３ ), Lantana (La ２ O ３ ), gadolinium oxide (Gd ２ O ３ 17. The layered catalyst composite of claim 1, comprising ceria, in combination with a cation exchanger, ...

18. The second layer is a rhodium component impregnated in said OSC containing ceria; and alumina The layered catalyst composite of any one of claims 1 to 17, comprising:

19. 19. The layered catalyst composite of any one of claims 1 to 18, wherein the second layer further comprises a PGM component selected from palladium, platinum, and combinations thereof.

20. 20. The layered catalyst composite of claim 1, wherein the catalytic material comprises platinum, palladium, and rhodium, wherein the mass ratio of platinum to palladium is in the range of 1 / 5 to 20 / 1, and the mass ratio of platinum to rhodium is in the range of 1 / 2 to 20 / 1.

21. 21. The layered catalyst composite of any one of claims 1 to 20, wherein the substrate is a wall-flow filter substrate or a flow-through substrate.

22. 22. The layered catalyst composite of claim 1, wherein the first layer is disposed directly on a substrate and the second layer is disposed on top of the first layer.

23. 23. The layered catalyst composite of claim 1, wherein the second layer is disposed directly on a substrate and the first layer is disposed on top of the second layer.

24. 24. A method of reducing NOx levels in an exhaust gas stream during a fuel cut event, comprising contacting the exhaust gas stream with the layered catalyst composite of any one of claims 1 to 23 for a time and at a temperature sufficient to reduce NOx levels in the exhaust gas stream.

25. N in tailpipe exhaust ２ 24. A method for reducing O levels in tailpipe exhaust, comprising: passing an exhaust gas stream through a layered catalyst composite according to any one of claims 1 to 23 and a comparative TWC catalyst disposed further downstream. ２ contacting for a time and at a temperature sufficient to reduce the O level.

26. 1. An emission treatment system comprising: an engine producing an exhaust gas stream; A device for reducing CO and HC and converting NOx to N, disposed downstream of the engine and in fluid communication with the exhaust gas flow. ２ TWC articles adapted for conversion into A layered catalyst composite according to any one of claims 1 to 23, disposed downstream of a TWC article.

1. An exhaust treatment system comprising:

27. 27. The emissions treatment system of claim 26, wherein the engine is a gasoline engine.

28. 28. The emissions treatment system of claim 26 or 27, wherein the TWC article is in a first close-coupled location and the layered catalyst composite is in a second close-coupled location or an underfloor location.

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