A three-way catalyst containing multiple oxygen storage components.

Abstract

This disclosure relates to a ternary conversion (TWC) catalyst effective for reducing NOx, hydrocarbons, and carbon monoxide from gasoline engine exhaust gases, wherein the catalyst comprises a substrate having a first platinum group metal (PGM) component and optionally a second PGM component disposed on the substrate, a) the first PGM component comprising Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana, and b) the second PGM component comprising at least partially deposited on a second OSC doped with lantana.

Description

Technical Field

[0001] The present disclosure relates to a three-way conversion (TWC) catalyst composition and a catalyst article useful for treating exhaust gas from an internal combustion engine of an automobile and reducing pollutants contained therein. In particular, the present invention relates to a catalyst composition and a catalyst article containing platinum group metals.

Background Art

[0002] Various catalysts and catalyst systems are known for the treatment of exhaust gas from internal combustion engines that generally contain pollutants such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). These pollutants need to be substantially removed from the exhaust gas in order to meet strict government regulations. Three-way conversion (TWC) catalysts are commonly used to treat exhaust gas emitted from gasoline-powered vehicles. TWC catalysts and related systems are based on platinum group metals (PGMs) such as platinum, palladium, and rhodium. In recent years, there has been renewed interest in the automotive industry in using Pt for TWC applications in view of current low prices in the market. Commercially available Pd-Rh-based TWC catalysts typically use ceria-zirconia doped with lanthanum as an oxygen storage component (OSC). Such lanthanum-doped OSCs can be activated by Pd and / or Rh, but may not be fully activated when Pt is present as an active catalyst component. As a result, there is a need to discover an OSC material that can be effectively activated by Pt.

Summary of the Invention

[0003] The present invention provides a ternary conversion (TWC) catalyst effective in reducing NOx, hydrocarbons, and carbon monoxide from gasoline engine exhaust gas, wherein the catalyst comprises a substrate having a first platinum group metal (PGM) component and optionally a second PGM component disposed on the substrate, a) the first PGM component comprises Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana, and b) the second PGM component comprises at least partially deposited on a second OSC doped with lantana.

[0004] Further providing is an exhaust gas treatment system comprising a gasoline engine and a three-way converter (TWC) catalyst downstream of the engine, and a method for treating exhaust gas from a gasoline engine, including contacting the exhaust gas with the TWC. [Brief explanation of the drawing]

[0005] [Figure 1] The graph shows the light-off temperature of a 2% Pt / OSC sample using the powder TWC light-off test protocol (lambda=1) after lean / rich cycle aging at 1000°C for 5 hours. [Figure 2] The graph shows the light-off temperature of a 2% Pd / OSC sample using the powder TWC light-off test protocol (lambda=1) after lean / rich cycle aging at 1000°C for 5 hours. [Figure 3] The graph shows the light-off temperature of a 0.5% Rh / OSC sample using the powder TWC light-off test protocol (lambda=1) after lean / rich cycle aging at 1000°C for 5 hours. [Figure 4] The graph shows the light-off temperature of a 1%Pt-0.25%Rh / OSC sample using the powder TWC light-off test protocol (lambda=1) after lean / rich cycle aging at 1000°C for 5 hours. [Figure 5] The graph shows the oxygen storage capacity of 2% Pt / OSC samples using the powder OSC test protocol after lean / rich cycle aging at 1000°C for 5 hours. [Figure 6]The graph shows the oxygen storage capacity of 1%Pt-0.25%Rh / OSC samples using the powder OSC test protocol after lean / rich cycle aging at 1000°C for 5 hours. [Figure 7] The chart shows the Pt crystallite size of 2% Pt on 30% CeO2OSC from the Rietveld method at approximately 39.5° theta angle of the Pt(111) plane, obtained by X-ray diffraction (XRD) after lean / rich aging at 1000°C for 5 hours. [Figure 8A] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 8B] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 8C] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 8D] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 8E] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 8F] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 8G] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 8H] A schematic diagram of a typical TWC catalyst (OSC-1: first oxygen storage component; OSC-2: second oxygen storage component) is shown. [Figure 9A] This is a perspective view of a honeycomb-type substrate support that may include a TWC catalyst composition according to one embodiment of the invention claimed in this application. [Figure 9B]Figure 9A shows an enlarged view of the multiple gas channels shown in Figure 9A, and is a partial cross-sectional view taken along a plane parallel to the end face of the substrate carrier in Figure 9A. [Modes for carrying out the invention]

[0006] It should be understood that the following disclosure describes several exemplary embodiments for carrying out different features, structures, and / or functions of the present invention. Exemplary embodiments of components, arrangements, and configurations are described below for the sake of brevity of this disclosure, but these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the present invention. In addition, this disclosure may repeat reference numerals and / or letters in various exemplary embodiments and across the figures provided herein. This repetition is for the sake of brevity and clarity and does not in itself define the relationships between the various exemplary embodiments and / or configurations discussed in the figures. Furthermore, exemplary embodiments can be used in other exemplary embodiments without departing from the scope of this disclosure.

[0007] All methods described herein may be carried out in any preferred order unless otherwise indicated herein or expressly rejected by the context. The use of any and all examples or illustrative terms provided herein (e.g., "etc.") is solely intended to better illustrate the materials and methods and does not impose any limitation on their scope unless otherwise claimed.

[0008] As used herein, the terms “catalyst” or “catalytic composition” refer to a material that facilitates a reaction.

[0009] The term "NOx" refers to nitrogen oxide compounds such as NO and / or NO2.

[0010] Terms such as "exhaust stream", "engine exhaust stream", "exhaust gas stream" refer to any combination of flowing engine effluent gas that may similarly contain solid or liquid particulate matter. This stream contains gaseous components and, for example, is the exhaust of a lean burn engine, which may contain certain non-gaseous components such as droplets, solid particles, etc. The exhaust stream of a lean burn engine typically further includes combustion products, incomplete combustion products, nitrogen oxides, combustible and / or carbonaceous particulate matter (soot), and unreacted oxygen and / or nitrogen. Such terms also refer to the effluent downstream of one or more other catalyst system components as described herein.

[0011] "BET surface area" has its ordinary meaning, referring to the multi-layer adsorption (Brunauer-Emmett-Teller) method for determining surface area by N2 adsorption measurement. Unless otherwise specified, all references in this specification to "specific surface area" or "surface area" refer to the BET surface area.

[0012] The platinum group metal (PGM) component refers to any component containing PGM (e.g., Rh, Pd, and Pt). For example, the PGM may be in the zero-valent metal form or the PGM may be in the oxide form. References to "PGM component" allow for the presence of PGM in any valence state. Terms such as "platinum (Pt) constituent", "rhodium (Rh) constituent", "palladium (Pd) constituent", etc. refer to the respective platinum group metal compounds, complexes, etc., which decompose or otherwise convert to a catalytically active form, usually a metal or metal oxide, upon firing or use of the catalyst.

[0013] The term "catalytic article" or "catalyst article" refers to a component in which a substrate is coated with a catalyst composition used to promote a desired reaction. These compositions may be referred to as washcoats.

[0014] As used herein, the "support" in a catalyst material, catalyst composition, or catalyst washcoat refers to a material that can receive metals (e.g., PGM), stabilizers, promoters, binders, etc. by precipitation, association, dispersion, impregnation, or other suitable methods.

[0015] As used herein, the term "oxygen storage component" (OSC) refers to an entity that has multiple valence states and can react actively with reducing agents such as carbon monoxide (CO) and / or hydrogen under reducing conditions, and then can react with oxidizing agents such as oxygen or nitrogen oxides under oxidizing conditions. Examples of oxygen storage components include, optionally, early transition metal oxides, especially ceria composites doped with zirconia, lanthana, praseodymia, neodymia, niobia, europia, samaria, ytterbia, yttria, and mixtures thereof. The oxygen storage component is also commonly used as a carrier material for PGM in TWC catalysts.

[0016] As used herein, the term "substrate" typically refers to a monolithic material on which a catalyst composition is disposed in the form of a washcoat containing a plurality of particles that contain the catalyst composition. References to a "monolithic substrate" or "honeycomb substrate" mean a single structure that is homogeneous and continuous from an inlet to an outlet.

[0017] As used herein, the term "washcoat" has its ordinary meaning in the art and refers to a thin adhesive coating of a catalyst material or other material applied to a substrate material such as a honeycomb-shaped carrier member that is porous enough to allow the passage of the gas stream to be treated. <00**********3> A washcoat is formed by preparing a slurry containing particles of a solid content (e.g., 20 - 60 wt%) in a liquid vehicle, then coating this on the substrate and drying it to provide a washcoat layer.

[0019] As used herein, the wash coat layer comprises compositionally different materials disposed on or beneath the surface of a monolithic substrate. In one embodiment, the substrate may contain one or more wash coat layers, each wash coat layer being different in some respect (e.g., different physical properties such as particle size or microcrystalline phase) and / or different chemical catalytic functions.

[0020] A catalyst article may be "fresh," meaning it is new and has not been exposed to heat or thermal stress for an extended period. "Fresh" may also mean that the catalyst has been recently prepared and has not been exposed to any exhaust gases or high temperatures. Similarly, an "aged" catalyst article is not fresh and has been exposed to exhaust gases and high temperatures (i.e., above 500°C) for an extended period (i.e., more than 3 hours).

[0021] As used herein, the term “flow” broadly refers to any combination of fluid gases that may contain solid or liquid particulate matter.

[0022] As used herein, the terms “upstream” and “downstream” refer to the relative direction of the flow of engine exhaust gases from the engine to the exhaust pipe, with the engine in the upstream position and the tailpipe and any contamination control items such as filters and catalysts located downstream of the engine.

[0023] In TWC design, Pt is either compounded separately or incorporated together with Pd (or Rh) in a layer or zone. Conventional OSC materials designed for Pd and / or Rh activation have commonly been used in Pt-containing TWC catalysts where Pt also interacts with such OSCs. However, recent research by the applicant has shown that Pt is a relatively inferior OSC activator compared to Pd and Rh, and that La2O3 can be an OSC "scavenger" under Pt activation. As a result, the applicant aimed to develop an OSC material that is selectively effective for Pt activation, unlike existing Pt-containing TWC catalysts.

[0024] This disclosure provides a TWC technology using multiple oxygen storage components (OSCs) that can be selectively activated by PGM packages such as Pt-Pd-Rh, Pt-Rh, and Pt-Pd. More specifically, Pt is applied to activate a first OSC that is essentially La2O3-free, while Pd and / or Rh are optionally applied to activate a second OSC that contains La2O3.

[0025] The advantages of the TWC catalyst of this disclosure include improved performance in TWC light-off and oxygen storage capacity compared to Pt on La2O3-containing OSCs at the powder level. In addition, Pt on La2O3-free OSCs provides smaller Pt crystallites than Pt on La2O3-containing OSCs, according to XRD.

[0026] In one embodiment, a ternary conversion (TWC) catalyst effective in reducing NOx, hydrocarbons, and carbon monoxide from gasoline engine exhaust gas comprises a substrate having a first platinum group metal (PGM) component and optionally a second PGM component, wherein a) the first PGM component comprises Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana, and b) optionally, the second PGM component is at least partially deposited on a second OSC doped with lantana.

[0027] In one embodiment, the first PGM component further comprises Rh.

[0028] In one embodiment, the second PGM component includes at least Pd, Rh, or a combination thereof.

[0029] In one embodiment, the first OSC contains ceria in an amount of 5 to 75% by weight, based on the total weight of the first OSC.

[0030] In one embodiment, the TWC and the first OSC contain zirconia in an amount of 25 to 95% by weight, based on the total weight of the first OSC.

[0031] In one embodiment, the first OSC substantially does not contain any rare earth metal oxides other than CeO2.

[0032] In one embodiment, the first OSC comprises a dopant selected from yttria, praseodymia, neodymia, and combinations thereof. In other embodiments, the first OSC comprises a total amount of yttria, praseodymia, neodymia, and combinations thereof, up to about 15% by weight, based on the weight of the first OSC.

[0033] In one embodiment, the second OSC further comprises a dopant selected from yttria, praseodymia, neodymia, and combinations thereof. In other embodiments, the second OSC comprises a total amount of yttria, praseodymia, lantana, neodymia, and combinations thereof, up to about 15% by weight, based on the weight of the second OSC.

[0034] In one embodiment, the substrate is a honeycomb substrate, and the first PGM component and the second PGM component are mixed in a single layer on the substrate.

[0035] In one embodiment, the first PGM component is located in the first layer, and the second PGM component is located in the second layer on the substrate.

[0036] In one embodiment, the first PGM component is located in a first layer directly on the substrate, and the second PGM component is located in a second layer above the first layer.

[0037] In one embodiment, the second PGM component is located in a second layer directly on the substrate, and the first PGM component is located in a first layer above the second layer.

[0038] In one embodiment, the substrate has an axial length, an upstream end, and a downstream end, with the first PGM component located at the downstream end and the second PGM component located at the upstream end.

[0039] In one embodiment, the substrate is a wall flow filter having alternating inlet and outlet passages.

[0040] In one embodiment, the first PGM component contains about 0.01 to about 5% by weight of Pt, based on the total wash coat load.

[0041] In one embodiment, the second PGM component comprises a total amount of Pd, Rh, or a combination thereof, based on the total wash coat load, ranging from about 0.01 to about 5% by weight.

[0042] In one embodiment, the ternary converter (TWC) catalyst is incorporated into an exhaust gas treatment system, including a gasoline engine, and the ternary converter (TWC) catalyst is located downstream of the engine.

[0043] Some embodiments include a method for treating exhaust gases from a gasoline engine, which comprises contacting the exhaust gases with a three-way catalytic converter (TWC) of the present disclosure.

[0044] In one exemplary embodiment, the first PGM component deposited on the first oxygen storage component (OSC) is a lower layer on the substrate. Optionally, a second PGM component is deposited at least partially on the second OSC as an upper layer on the lower layer.

[0045] In another embodiment, the catalyst article comprises a first layer comprising a first PGM component comprising Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana. As used herein, “substantially free of lantana” means that lantana is not added externally, although lanthane may optionally be present in trace or nominal amounts of <0.1%.

[0046] In some examples, the first PGM component contains Pt in an amount of about 0.01 to about 5% by weight, preferably about 0.1 to 2% by weight, and more preferably about 0.2 to 1.5% by weight, based on the total wash coat load. Optionally, the first PGM component may further contain Rh in an amount of about 0.01 to about 1% by weight, preferably about 0.02 to 0.5% by weight, and more preferably about 0.05 to 0.2% by weight, based on the total wash coat load.

[0047] The first OSC may contain ceria in an amount of 5 to 75% by weight, preferably 10 to 50% by weight, and more preferably 20 to 40% by weight, based on the total weight of the first OSC. The first OSC may also contain zirconia in an amount of 25 to 95% by weight, preferably 40 to 90% by weight, and more preferably 45 to 80% by weight, based on the total weight of the first OSC components. In some examples, the first OSC may not contain substantially any rare earth metal oxides other than CeO2. As used herein, the term “substantially free of rare earth metal oxides other than CeO2” means that no rare earth metal oxides other than CeO2 have been added from the outside, although they may optionally be present in trace or nominal amounts of <0.1%.

[0048] In some examples, the first OSC may include a dopant selected from yttria, praseodymia, neodymia, and combinations thereof. In some examples, the first OSC may include a total amount of yttria, praseodymia, neodymia, and combinations thereof, up to about 15% by weight, up to about 10% by weight, or up to about 5% by weight, based on the weight of the first OSC.

[0049] Examples of the first oxygen storage component include ceria-zirconia, ceria-zirconia-yttria, ceria-zirconia-neodymia, ceria-zirconia-praseodymia, or combinations thereof. In one embodiment, the oxygen storage component includes ceria-zirconia. In one embodiment, the first oxygen storage component is in a fresh state for 40 ml. 2 / g~120m 2 It has a BET specific surface area in the range of / g. In another embodiment, the first OSC is aged at 1000°C for 5 hours in the presence of periodic lean and rich atmospheres, and then 15m 2 / g~60m 2 Maintain a BET specific surface area within the range of / g.

[0050] Optionally, the TWC may further include a second PGM component at least partially deposited on a second OSC doped with lantana. If a second PGM component is included, the first PGM component may be deposited on a first layer on the substrate, and the second PGM component may be deposited on a second layer on the substrate. In some examples, the second PGM component may be present directly on the substrate, or it may be at least partially overlapping the first layer containing the first PGM component.

[0051] The second PGM component may include at least Pd, Rh, or a combination thereof. Optionally, the second OSC may further include, based on the weight of the second OSC, a total amount of dopants selected from yttria, praseodymia, lantana, neodymia, and combinations thereof, up to approximately 15% by weight, up to approximately 10% by weight, or up to approximately 5% by weight.

[0052] Examples of second oxygen storage components include ceria-zirconia-lantana, ceria-zirconia-lantana-yttria, ceria-zirconia-lantana-neodymia, ceria-zirconia-lantana-praseodymia, ceria-zirconia-lantana-neodymia-praseodymia, or combinations thereof.

[0053] According to one or more embodiments, the substrate for the catalyst article of the present disclosure may consist of any material typically used to prepare automotive catalysts, and typically includes a ceramic or metallic monolithic honeycomb structure. The substrate is typically to which a wash coat containing the catalyst composition described herein is applied and bonded, thereby providing a plurality of walls that act as a carrier for the catalyst composition.

[0054] Examples of metal 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 may contain one or more nickel, chromium, and / or aluminum, and the total amount of these metals may, advantageously, contain at least 15 wt% of the alloy, e.g., 10-25 wt% of chromium, 3-8 wt% of aluminum, and up to 20 wt% of nickel. The alloys may also contain small or trace amounts of one or more metals such as manganese, copper, vanadium, and titanium. To improve the corrosion resistance of the alloy and promote adhesion of the wash coat layer to the metal surface by forming an oxide layer on the surface of the substrate, the surface of the metal substrate may be oxidized at a high temperature, for example, above 1000°C.

[0055] Any suitable refractory material can be used to construct the substrate, such as cordierite, mullite, cordierite-alumina, silicon nitride, zircon mullite, siecite, alumina-silica-magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, and aluminosilicate. Any suitable substrate may be used, such as a monolithic flow-through substrate having multiple fine parallel gas channels extending from the inlet to the outlet surface of the substrate so that the channels are open to the fluid flow. The channels, which are essentially straight paths from inlet to outlet, are defined by walls coated with a catalyst material as a wash coat so that the gas flowing through the channels comes into contact with the catalyst material. The channels in the monolithic substrate are thin-walled channels of any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, and circular. Such structures contain approximately 60 to 1200 or more gas inlet openings (i.e., "cells") (cpsi) per square inch of cross-section, more commonly around 300 to 600 cpsi. The wall thickness of flow-through substrates can vary, but a typical range is 0.002 to 0.1 inches. Typical commercially available flow-through substrates are cordierite substrates with 400 cpsi and 6 mil wall thickness, 600 cpsi and 4 mil wall thickness, or 900 cpsi and 2 mil wall thickness. However, it will be understood that the present invention is not limited to any particular type, material, or shape of substrate.

[0056] In an alternative embodiment, the substrate may be a wall-flow substrate, where each passage is blocked by a non-porous plug at one end of the substrate body, and alternating passages are blocked at opposing end faces. This requires the gas to flow through the porous walls of the wall-flow substrate to reach the outlet. Such a monolithic substrate can contain up to about 700 cpsi or more, for example, about 100-400 cpsi, more typically about 200-300 cpsi. The cross-sectional shape of the cell can vary as described above.

[0057] Wall flow substrates typically have a wall thickness of 0.002 to 0.1 inches. Typical commercially available wall flow substrates are constructed from porous cordierite, examples of which have a wall thickness of 200 cpsi and 10 mils or a wall thickness of 300 cpsi and 8 mils, and a wall porosity of 45 to 65%. Other ceramic materials such as aluminum titanate, silicon carbide, and silicon nitride are also used as wall flow filter substrates. However, it will be understood that the present invention is not limited to a particular type, material, or shape of substrate. It should be noted that when the substrate is a wall flow substrate, the catalyst composition can penetrate into the pore structure of the porous wall in addition to being placed on the surface of the wall (i.e., partially or completely blocking the pore openings). In one embodiment, the substrate has a flow-through ceramic honeycomb structure, a wall flow ceramic honeycomb structure, or a metal honeycomb structure.

[0058] In one embodiment, the catalyst article described herein comprises a) a first PGM component comprising Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana. Optionally, the first PGM component may further comprise Pd and / or Rd. Optionally, the catalyst does not comprise a second PGM component.

[0059] In one embodiment, the catalyst article described herein includes a layered arrangement. The layered arrangement may include: a) a first layer comprising a first PGM component comprising Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana; b) a second PGM component comprising a second OSC doped with lantana at least partially deposited; and c) a substrate. The second layer may be deposited as an underlayer on the substrate accompanied by the first layer deposited on the substrate. Alternatively, the first layer may be deposited as an underlayer on the substrate accompanied by the second layer deposited on the substrate. Optionally, the first PGM component may further contain Rh.

[0060] In one embodiment, the catalyst article described herein includes a zone arrangement. The zone arrangement consists of a forward zone (first zone) and a backward zone (second zone). In one embodiment, the TWC article includes a) a first layer comprising a first PGM component comprising Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana; b) a second PGM component comprising a second OSC doped with lantana at least partially deposited; and c) a substrate, wherein the first or second layer is deposited on the substrate as an upper or lower layer, and at least one of the first and second layers has a zone arrangement comprising a first zone and a second zone, the first or second zone covering 40 to 90% of the length of the substrate.

[0061] In one embodiment, the first layer includes a front zone (first zone) or a rear zone (second zone), which covers 40-90% of the length of the substrate. In another embodiment, the second layer includes a front zone (first zone) or a rear zone (second zone), which covers 40-90% of the length of the substrate. Preferably, the second PGM component is located on the first zone (upstream end) and the first PGM component is located on the second zone (downstream end), but other arrangements are also possible.

[0062] In one embodiment of the zone arrangement, the TWC article may further include a third layer comprising a PGM component at least partially deposited on a substantially lantana-free oxygen storage component (OSC), the third layer being at least partially located in the first and second zones. The third layer may be deposited as an upper or lower layer on the substrate. Optionally, the PGM component of the third layer may be Rh or Rh+Pt.

[0063] Figures 8A to 8H show exemplary, non-limiting configurations of layered and zoned TWC catalysts.

[0064] Figures 9A and 9B show an exemplary, non-limiting substrate 2 of a flow-through substrate coated with the catalyst composition described herein. Referring to Figure 9A, the exemplary substrate 2 has a cylindrical shape and has a cylindrical outer surface 4, an upstream end surface 6, and a corresponding downstream end surface 8 which is identical to the end surface 6. Multiple fine, parallel gas channels 10 are formed within the substrate 2. As can be seen from Figure 9B, the channels 10 are formed by walls 12 that extend through the substrate 2 from the upstream end surface 6 to the downstream end surface 8, and the channels 10 are not blocked so that a fluid, such as a gas flow, passing longitudinally through the substrate 2 can flow through the gas channels 10. As can be seen more readily in Figure 9B, the walls 12 are dimensioned and constructed so that the gas channels 10 have a substantially regular polygonal shape. As shown in the figures, the washcoat composition can be applied in multiple separate layers if desired. In the illustrated embodiment, the wash coat comprises a separate first wash coat layer 14 adhered to the wall 12 of the base material member, and a separate second wash coat layer 16 coated on the first wash coat layer 14. In one embodiment, the three-way catalyst may be provided as two or more (e.g., three or four) wash coat layers, and is not limited to the two-layer embodiment shown.

[0065] A porous wall flow filter is catalytic in that the walls of the element have one or more catalytic materials on them or contain one or more catalytic materials within them. The catalytic material may be present only on the inlet side of the element wall, only on the outlet side, on both the inlet and outlet sides, or the wall itself may consist of all or part of the catalytic material. The present invention includes using one or more layers of catalytic material on the inlet and / or outlet walls of an element.

[0066] In yet another aspect, the present invention provides a process for preparing a TWC catalyst article. The process includes the following steps:

[0067] In the first step, a lower slurry is prepared and then deposited onto the substrate. Separately, an upper slurry is prepared and deposited on top of the lower slurry, followed by firing at a temperature in the range of 400-700°C. The steps for preparing the lower and upper layers include techniques such as initial wet impregnation, initial wet co-impregnation, and post-addition. In one embodiment, the process includes firing the substrate coated with the lower layer before coating with the upper layer. Typically, firing is carried out at a temperature in the range of 400-700°C.

[0068] Initial wet impregnation techniques, also known as capillary impregnation or dry impregnation, are commonly used in the synthesis of heterogeneous materials, i.e., catalysts. Typically, an active metal precursor is dissolved in an aqueous or organic solution, and then the metal-containing solution is added to a catalyst support containing the same pore volume as the volume of the added solution. Capillary action draws the solution into the pores of the support. If the solution is added beyond the pore volume of the support, the solution transport changes from a capillary process to a much slower diffusion process. The catalyst is 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. Multiple active metal precursors can be co-impregnated onto the catalyst support after appropriate dilution. Alternatively, active metal precursors are introduced into the slurry via post-addition under stirring during the slurry preparation process.

[0069] The carrier particles are typically dry enough to absorb substantially all of the solution and form a moist solid. Typically, aqueous solutions of water-soluble compounds or complexes of the active metal are used, such as rhodium chloride, rhodium nitrate, rhodium acetate, or combinations thereof in which rhodium is the active metal, and palladium nitrate, palladium tetraamine, palladium acetate, or combinations thereof in which palladium is the active metal. After treating the carrier particles with the active metal solution, the particles are dried by heat treatment at a high temperature (e.g., 100-150°C) for a certain period of time (e.g., 1-3 hours), and then calcined to convert the active metal into a more catalytically active form. An exemplary calcination process involves heat treatment in air at a temperature of about 400-550°C for 10 minutes to 3 hours. The above process may be repeated as necessary to achieve the desired level of active metal impregnation.

[0070] The catalyst compositions described above are typically prepared in the form of catalyst particles as described above. These catalyst particles are mixed with water to form a slurry for coating a catalyst substrate, such as a honeycomb substrate. In addition to the catalyst particles, the slurry may 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 exemplary binders include boehmite, gamma-alumina, or delta / theta alumina, and silica sol. If present, the binder is typically used in an amount of about 1–5% by weight of the total washcoat load. Acidic or basic species are 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 solution, or acetic acid. The typical pH range of the slurry is about 3–12.

[0071] The slurry can be pulverized to reduce the particle size and promote particle mixing. Pulverization is achieved using a ball mill, continuous mill, or other similar equipment, and the solid content of the slurry may be, for example, about 20–60% by weight, more specifically about 20–40% by weight. In one embodiment, the pulverized slurry is characterized by a D90 particle size of about 10–40 micrometers, preferably 10–30 micrometers, and more preferably about 10–15 micrometers. D90 is determined using a dedicated particle size analyzer. The equipment used in this example measures the particle size in a small volume slurry using laser diffraction. Typically, D90 in micrometers means that 90% of the particles have a diameter less than that value.

[0072] The slurry is coated onto the catalyst substrate using any wash-coat technique known in the art. In one embodiment, the catalyst substrate is immersed in the slurry one or more times, or otherwise coated with the slurry. The coated substrate is then dried at a high temperature (e.g., 100-150°C) for a certain period (e.g., 10 minutes to 3 hours), and then calcined by heating at, for example, 400-700°C, typically for about 10 minutes to about 3 hours. After drying and calcining, the final wash-coat coating layer is considered to be essentially solvent-free. After calcining, the amount of catalyst supported by the wash-coat technique described above can be determined by calculating the difference between the coated weight and the uncoated weight of the substrate. As will be apparent to those skilled in the art, the amount of catalyst supported can be changed by changing the slurry rheology. The coating / drying / calcining process for producing the wash-coat may be repeated as needed to build up the coating to a desired level of supported material or thickness, meaning that more than one wash-coat may be applied.

[0073] In certain embodiments, the coated substrate is aged by subjecting the coated substrate to heat treatment. In one embodiment, the aging is carried out for 20 hours at a temperature of about 850°C to about 1050°C in an environment of volume % water in air. Thus, in certain embodiments, an aged catalyst article is provided. In certain embodiments, a particularly effective material is a metal oxide-based support (including, but not limited to, substantially 100% ceria support) that maintains a high percentage (e.g., about 95-100%) of its pore volume after aging (e.g., aging at about 850°C to about 1050°C, 10 volume % water in air, for 20 hours).

[0074] In another embodiment, the present invention provides an exhaust system for an internal combustion engine comprising a catalyst article comprising the TWC composition described herein. In one embodiment, the exhaust system comprises a TWC catalyst article comprising: a) a first layer comprising a first PGM component comprising Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lanthanum; b) any second PGM component at least partially deposited on a second OSC doped with lanthanum; and a substrate.

[0075] In one embodiment, the exhaust system includes the ternary converter (TWC) catalyst article described herein, and the ternary converter (TWC) catalyst article is located downstream of an internal combustion or gasoline engine.

[0076] In one embodiment, the Disclosure also provides a method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides. The method involves bringing the exhaust stream into contact with a catalyst composition or catalyst article or exhaust system according to the present invention. Terms such as “exhaust stream,” “engine exhaust stream,” and “exhaust gas stream” refer to any combination of flowing engine exhaust gases, which may also contain solid or liquid particulate matter. This stream contains gaseous components, such as the exhaust from a lean-burn engine, which may contain certain non-gaseous components such as droplets and solid particles. The exhaust stream from a lean-burn engine typically contains combustion products, incomplete combustion products, nitrogen oxides, flammable and / or carbonaceous particulate matter (soot), and unreacted oxygen and / or nitrogen. Such terms also refer to downstream effluents of one or more other catalytic system components, as described herein.

[0077] In another embodiment, the present invention also provides a method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream. The method involves bringing the gaseous exhaust stream into contact with a catalyst composition or catalyst article or exhaust system according to the present invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0078] In some embodiments, the catalyst article converts hydrocarbons into carbon dioxide and water. In some embodiments, the catalyst article converts at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 90%, or at least about 95% of the amount of hydrocarbons present in the exhaust gas stream before contact with the catalyst article. In some embodiments, the catalyst article converts carbon monoxide into carbon dioxide. In some embodiments, the catalyst article converts at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 90%, or at least about 95% of the amount of carbon monoxide present in the exhaust gas stream before contact with the catalyst article. In some embodiments, the catalyst article converts nitrogen oxides into nitrogen.

[0079] In some embodiments, the catalyst article converts at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 90%, or at least about 95% of the amount of nitrogen oxides present in the exhaust gas stream before contact with the catalyst article. In some embodiments, the catalyst article converts at least about 50%, at least about 60%, at least about 70%, at least about 80%, 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 before contact with the catalyst article. [Examples]

[0080] Examples 1A-M: OSC materials. Table 1 shows the compositions of a series of ceria-zirconia-based OSC materials, including those with different ceria content and dopant packages. Example 1C is a dopant-free material, while the other examples have dopant packages of 5-10% by weight of La2O3, Y2O3, and / or Nd2O3.

[0081] [Table 1]

[0082] Example 2: Preparation and molding of PGM / OSC powder samples. The OSC materials from Examples 1A to 1M were impregnated with 2% Pt, 2% Pd, 0.5% Rh, or 1% Pt-0.25% Rh. 2-3 g of each PGM / OSC sample was prepared and sized using the following workflow:

[0083] Step 1. Sample preparation: OSC material was impregnated with the target amount of PGM using Pt-nitrate (CAS: 18496-40-7, Umicore AG & Co KG), Pd-nitrate (CAS: 32916-07-7, Umicore AG & Co KG), Rh-nitrate (CAS: 10139-58-9, Umicore AG & Co KG), or a mixture of Pt-nitrate and Rh-nitrate solutions (100% initial wetting, concentration adjusted to match the target amount and water absorption of the OSC material). The impregnated powder was thoroughly mixed to ensure uniform dispersion. The resulting mixture was dried at 120°C and then calcined in air at 550°C for 2 hours.

[0084] Step 2. Sample Forming: The calcined powder from Step 1 was mixed with deionized water to obtain a solid content of approximately 30% by weight. A dispersion of boehmite in water (DISPAL® 23N4-80, Sasol) equivalent to 5% by weight of Al2O3 relative to OSC was added. The mixture was dried with stirring at 120°C. The dried cake was calcined in air at 550°C for 2 hours. The resulting powder was pulverized and then sieved to collect particles with a diameter of 250-500 μm for aging and testing.

[0085] Example 3: Aging of powder samples. A portion of each molded sample from Example 2 was aged for 5 hours in a box furnace at 1000°C in a gas flow containing 10% steam. After heating at a rate of 5°C / min in steam / air, the gas flow was switched between steam / air (lean, 10 min) and steam / forming gas (4% H2 in N2, rich, 10 min). Cooling was performed in steam / air. After the temperature dropped below 400°C, the steam supply was stopped and the samples were further cooled to room temperature in dry air.

[0086] Example 4: High-throughput TWC light-off test of powder samples. The TWC light-off test was performed using a 48x parallel test unit. Each 105 mg aged sample from Example 3 was diluted to a volume of 1 mL with corundum of the same particle size fraction and placed in a stainless steel reactor with a bore diameter of 7 mm. The samples were subjected to 70 K h with a specified mean λ value (i.e., the ratio of the actual air-fuel ratio to the stoichiometric air-fuel ratio). -1 The gas was exposed to a gas supply at a constant flow rate and fluctuating composition (1 second lean and 1 second rich) at a gas hourly space velocity (GHSV). The concentrations of the supplied components in the lean and rich gases are shown in Table 2. The actual λ values ​​were measured using a λ sensor (Bosch, planar broadband sensor "LSU 4.9") and adjusted for the amount of oxygen supplied during the lean and rich supplies without disturbing the perturbation amplitude (parameter "Δ" in Table 2). Individual exhaust components were measured at a frequency of 1 Hz using an online gas analyzer (NO, NO2, NH3: ABB LIMAS; CO, CO2, N2O: ABB URAS; Total HC: ABB FIDAS; H2, H2O: Mass spectrometer, Pfeiffer Quadstar). For the light-off test, the mean of λ was adjusted to 1.00 (i.e., under average stoichiometric conditions, lean: λ=1.05, rich: λ=0.95). Next, the reactors were equilibrated to several separate temperatures (200, 225, 250, 275, 300, 325, 350, 375, 400, 425, and 450°C). At each temperature, the exhaust gas from each of the 48 reactors was sequentially switched to an analyzer, and each sample was exposed to an oscillating feed for a 150-second equilibrium time until it reached a steady state. Subsequently, the signal from each gas analyzer was recorded for 30 seconds, and the conversion rate was calculated by averaging these signals. To estimate the light-off temperature, discrete values ​​were numerically interpolated as a function of temperature, and T50 (temperature at 50% conversion rate) was calculated by applying a root-finding procedure to the interpolated function.

[0087] [Table 2]

[0088] The first TWC light-off test was applied as a degreening step for the powder catalyst, and the second light-off test was used for data analysis. The T50 values ​​for the 2%Pt, 2%Pd, 0.5%Rh, and 1%Pt-0.25%Rh samples are shown in Figures 2 to 5, respectively.

[0089] For the 2% Pt / OSC sample (Figure 1), a clear effect of the dopant package on the light-off temperature was observed. The HC / NOx / CO light-off T50 increased in the following order: i) 1E Ce30Zr65Y5 < 1C Ze30Zr70 < 1F Ce30Zr60La5Y5 < 1D Ce30Zr65La5, and ii) 1H Ce30Zr60Y10 < 1I Ce30Zr60Nd10 < 1G Ce30Zr60La10. These two orders indicate that Y2O3 may be a preferred dopant in the presence of Pt as a PGM component, while La2O3 may potentially be a toxic dopant. Similar effects were observed in other OSC pairs with 10%, 20%, and 40% CeO2 content. In contrast, the 2% Pd / OSC sample (Figure 2) did not exhibit such performance dependence on the dopant package. In the presence of Pd, almost all OSC materials performed similarly in the light-off test. The 0.5% Rh / OSC sample (Figure 3) showed only a very slight effect of the dopant package on the light-off temperature. However, the T50 data suggested that Y2O3 provided slightly better performance than La2O3 as a dopant. Interestingly, the dopant package had a significant effect on the performance of the 1% Pt-0.25% Rh / OSC sample (Figure 4). Here again, Y2O3 was preferred over La2O3 as a dopant. In addition, the light-off T50 of the Y2O3-doped 1% Pt-0.25% Rh sample was comparable to or better than that of the corresponding 0.5% Rh sample, demonstrating the potential for a Pt-Rh synergy to reduce the expensive Rh usage by approximately 50%.

[0090] Example 5: High-throughput oxygen storage capacity test of powder samples. The oxygen storage capacity test was performed using the same sample volume identified in the TWC light-off test, with 48 times the number of parallel test units. The reactor was heated to the specified temperature (450 or 350°C), and then the sample was heated to 60K h -1 The samples were exposed to alternating pulses of nitrogen gas containing 1% oxygen (lean) and nitrogen gas containing 2% carbon monoxide (rich) at a gas-space-time velocity (GHSV). The amount of CO2 formed during the rich phase was recorded at a frequency of 1 Hz using a mass spectrometer (Pfeiffer Quadstar). A total of 15 cycles were used, each with a lean and rich duration of 10 seconds. For sample ranking, the oxygen storage capacity measured over 15 10-second cycles was averaged and normalized to the amount of sample tested (i.e., μmol(CO2) formed per gram of sample). The amount of CO2 formed corresponds to the amount of oxygen atoms released from the PGM / OSC sample during the rich phase.

[0091] Figures 5 and 6 show the oxygen storage capacity of OSC samples impregnated with 2% Pt and 1% Pt-0.25% Rh, respectively. At the same CeO2 content, the Y2O3-doped sample showed significantly higher oxygen storage capacity than the corresponding La2O3-doped sample. Superior OSC materials with Pt activation are substantially La2O3-free. While we do not wish to be constrained by theory, these data suggest that La2O3 may be a “scavenger” for OSCs under Pt activation. These observations generally agree well with the light-off data described above. The 1% Pt-0.25% Rh sample also showed substantially higher oxygen storage capacity than the corresponding 2% Pt sample. As expected, oxygen storage capacity decreases in the order of 40% CeO2 > 30% CeO2 > 20% CeO2 > 10% CeO2 for the same dopant package.

[0092] Example 6: Pt particle size measurement by XRD method. A 2% Pt sample was selected from a 30% CeO2 OSC sample and subjected to powder X-ray diffraction (XRD) testing to estimate the Pt particle size. XRD measurements were performed using a theta / theta diffractometer (D8 Advance A25-X1-1A22C4B, Bruker AXS) equipped with a secondary graphite monochromator (Cu Kα1+2 radiation) and a scintillation detector. Diffraction data analysis was performed using the software package Topas-64 (v6, Bruker AXS), and the Pt crystallite size of the 2% Pt / OSC sample was calculated according to the Rietveld method.

[0093] As shown in Figure 7, the average Pt particle size of the Y2O3-doped OSC sample is significantly smaller than that of the La2O3-doped OSC sample after lean / rich cycle aging at 1000°C for 5 hours. These data correlate well with the performance of the corresponding OSC samples during TWC light-off and oxygen storage capacity tests. N2 adsorption / desorption measurements of the relevant samples were performed at 25.1–27.4 m 2 The BET surface area per g is given, indicating good thermal stability against aging. However, the BET surface area data does not correlate with catalytic performance results because the difference between samples is too small.

[0094] The foregoing descriptions of specific embodiments are essentially illustrative and not intended to limit the scope, application, or use of the invention, and are naturally subject to change. This disclosure is provided in relation to the non-limiting definitions and terms contained herein. These definitions and terms are not designed to function as limitations on the scope or practice of the invention, but are presented solely for illustrative and explanatory purposes. While processes or configurations are described as a sequence of individual steps or using specific materials, it should be understood that the steps or materials may be interchangeable so that the description of the invention may include multiple parts or steps arranged in many ways so that it is readily understandable to those skilled in the art.

[0095] Terms such as “first,” “second,” and “third” may be used herein to describe various elements, components, regions, and / or processes, but it will be understood that these elements, components, regions, layers, and / or processes should not be limited by these terms. These terms are used solely to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Accordingly, the “first element,” “component,” “region,” “layer,” or “section” described above may be referred to as the second (or other) element, component, region, layer, or section without departing from the teachings herein.

[0096] Furthermore, the terms used herein are for the purpose of describing specific embodiments only and are not intended to be limiting. Where used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form, which includes “at least one,” unless the content explicitly indicates otherwise. “Or” means “and / or.” Where used herein, the term “and / or” includes any and all combinations of one or more of the enumerated items relating to the subject. Where used herein, the terms “comprises” and / or “comprising,” or “includes” and / or “including” specify the presence of the described features, areas, integers, processes, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, areas, integers, processes, operations, elements, components, and / or groups thereof. The term “or combination thereof” means a combination that includes at least one of the aforementioned elements.

[0097] Certain embodiments and features are described using sets of numerical upper and lower limits. Unless otherwise specified, it should be understood that ranges are intended to include any combination of any two values, e.g., any combination of any lower limit and any upper limit, any combination of any two lower limits, and / or any combination of any two upper limits. Certain lower limits, upper limits, and ranges are described in one or more of the following claims. All numerical values ​​are given as "approximately" or "about" values, taking into account experimental errors and variations expected by those skilled in the art.

[0098] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as generally understood by those skilled in the art in which this disclosure pertains. Terms as defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meanings in the context of the relevant art and this disclosure, and it will be further understood that they should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0099] In addition to those shown and described herein, various modifications of the present invention will be apparent to those skilled in the art of the above description. Such modifications are also intended to fall within the scope of the appended claims.

[0100] The patents, publications, and applications referenced herein indicate the level of expertise of the art in the field relating to the present invention. These patents, publications, and applications are incorporated herein by reference to the same extent that each individual patent, publication, or application is incorporated herein by reference specifically and individually.

[0101] The foregoing description illustrates specific aspects of the present invention, but does not mean to limit its implementation.

Claims

1. A ternary conversion (TWC) catalyst effective in reducing NOx, hydrocarbons, and carbon monoxide from gasoline engine exhaust gas, wherein the TWC catalyst is The substrate includes a substrate having a wash coat disposed on the substrate, The aforementioned wash coat, a) A first PGM component comprising Pt at least partially deposited on a first oxygen storage component (OSC) substantially free of lantana, b) A ternary conversion (TWC) catalyst comprising a second PGM component at least partially deposited on a second OSC doped with lantana.

2. The TWC catalyst according to claim 1, wherein the first PGM component further comprises Rh.

3. The TWC catalyst according to claim 1, wherein the second PGM component comprises at least Pd, Rh, or a combination thereof.

4. The TWC catalyst according to claim 1, wherein the first OSC contains ceria in an amount of 5 to 75% by weight, based on the total weight of the first OSC.

5. The TWC catalyst according to claim 1, wherein the first OSC contains zirconia in an amount of 25 to 95% by weight, based on the total weight of the first OSC.

6. The aforementioned first OSC is CeO ２ The TWC according to claim 1, which substantially does not contain any other rare earth metal oxides.

7. The TWC catalyst according to claim 1, wherein the first OSC comprises a dopant selected from yttria, praseodymia, neodymia, and combinations thereof.

8. The TWC catalyst according to claim 7, wherein the first OSC comprises a total amount of yttria, praseodymia, neodymia, and combinations thereof, up to about 15% by weight, based on the weight of the first OSC.

9. The TWC catalyst according to claim 1, wherein the second OSC further comprises a dopant selected from yttria, praseodymia, neodymia, and combinations thereof.

10. The TWC catalyst according to claim 9, wherein the second OSC comprises, based on the weight of the second OSC, a total amount of yttria, praseodymia, lantana, neodymia, and combinations thereof, up to about 15% by weight.

11. The TWC catalyst according to claim 1, wherein the substrate is a honeycomb substrate, and the first PGM component and the second PGM component are mixed in a single layer on the substrate.

12. The TWC catalyst according to claim 1, wherein the first PGM component is in a first layer directly disposed on the substrate, and the second PGM component is in a second layer located above the first layer.

13. The TWC catalyst according to claim 1, wherein the second PGM component is in a second layer directly disposed on the substrate, and the first PGM component is in a first layer located above the second layer.

14. The TWC catalyst according to claim 1, wherein the substrate has an axial length, an upstream end, and a downstream end, the first PGM component is arranged in a first zone at the downstream end, and the second PGM component is arranged in a second zone at the upstream end.

15. The TWC catalyst according to claim [[13]]14, further comprising a third layer comprising a PGM component at least partially deposited on an oxygen storage component (OSC) substantially free of lantana, wherein the third layer is positioned to at least partially overlap the first zone and the second zone.

16. The TWC catalyst according to claim 1, wherein the catalyst does not contain the second PGM component.

17. The TWC catalyst according to claim 1, wherein the substrate is a wall flow filter having alternating inlet and outlet passages.

18. The TWC catalyst according to claim 1, wherein the first PGM component contains Pt in an amount of about 0.01 to about 5% by weight, based on the total wash coat load.

19. The TWC catalyst according to claim 1, wherein the second PGM component comprises a total amount of Pd, Rh, or a combination thereof, based on the total wash coat load, in an amount of about 0.01 to about 5% by weight.

20. An exhaust gas treatment system comprising a gasoline engine and a ternary converter (TWC) catalyst described in claim 1, located downstream of the engine.

21. A method for treating exhaust gas from a gasoline engine, comprising contacting the exhaust gas with a three-way catalytic converter (TWC) as described in claim 1.

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