Platinum-containing three-way catalysts for close-coupled engine applications.

Abstract

The present invention relates to a three-way catalyst (TWC) for treating exhaust gas streams containing oxides of nitrogen (NOx), carbon monoxide (CO) and hydrocarbons (HC), the three-way catalyst comprising platinum group metals (PGM), a refractory metal oxide support, and a carrier, the platinum group metals (PGM) comprising platinum, palladium and rhodium, methods and uses thereof.

Description

[Technical field]

[0001] The present invention relates to a catalyst for treating exhaust gas streams produced in automotive applications. The catalyst of the present invention is a three-way catalyst (TWC). The present invention also relates to a method of treating exhaust gas streams with a three-way catalyst, and a method of using the catalyst. [Background technology]

[0002] Effective exhaust gas treatment systems for automobiles have been developed and are now widely used. The three major pollutants from fuel engines include nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). These three pollutants are purged from the exhaust gas stream by using so-called three-way catalysts (TWC).

[0003] Three-way catalysts (TWCs) typically require high temperatures to efficiently and completely remove pollutants from the exhaust gas stream. However, high temperatures can adversely affect the stability and performance of the catalyst. For example, high temperatures can lead to a sintering process that reduces the surface area of ​​the catalyst. This results in poor catalyst performance.

[0004] One way to address this problem is to select a specific combination of platinum group metals (PGMs) and support materials to maintain catalyst function over time and increase catalyst stability against exposure to high temperatures. For example, most conventional close-coupled three-way conversion catalysts (TWCs) contain only palladium and rhodium as platinum group metals (PGMs).

[0005] Platinum group metals (PGM) are precious metals and are only available at a high cost. In particular, the cost of palladium is 50% higher than that of platinum. Therefore, the partial replacement of palladium by platinum in existing catalyst formulations would already have enormous cost-saving potential. However, platinum in particular is known to have very limited stability in three-way conversion catalysts, due to sintering processes observed at high engine temperatures. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an objective to design a three-way catalyst (TWC) with improved stability at high temperatures, which allows for a higher amount of platinum to be used as the platinum group metal (PGM) and which can avoid or at least partially replace other more expensive platinum group metals (PGMs).

[0007] The present invention solves this problem by providing an improved formulation for a three-way catalyst (TWC) that contains a relatively large amount of platinum replacing other more expensive platinum group metals (PGMs), while the TWC of the present invention exhibits very good stability and excellent performance at high engine temperatures. [Means for solving the problem]

[0008] A first aspect of the present invention relates to a three way catalyst (TWC) for treating an exhaust gas stream containing oxides of nitrogen (NOx), carbon monoxide (CO) and hydrocarbons (HC), comprising a platinum group metal (PGM), a refractory metal oxide support, and a carrier, wherein the platinum group metal (PGM) comprises platinum, palladium and rhodium.

[0009] In a preferred embodiment, the three-way catalyst (TWC) is in a close coupled position.

[0010] In another preferred embodiment, the three-way catalyst (TWC) comprises multiple washcoat layers including a bottom washcoat layer and a top washcoat layer.

[0011] In another preferred embodiment, the multiple washcoat layers consist of two washcoat layers, one bottom washcoat layer and one top washcoat layer.

[0012] In another preferred embodiment, the bottom washcoat layer comprises a combination of platinum and palladium as the platinum group metals (PGMs).

[0013] In another preferred embodiment, the top washcoat comprises a combination of palladium and rhodium as platinum group metals (PGMs).

[0014] In another preferred embodiment, the bottom washcoat layer comprises platinum and palladium as the only platinum group metals (PGMs) and / or the top washcoat layer comprises rhodium as the only platinum group metals (PGMs), preferably palladium and rhodium, and more preferably platinum, palladium and rhodium.

[0015] In another preferred embodiment, the refractory metal oxide support is selected from a mixture or mixed oxide of ceria and alumina, or lanthana-doped (L-doped) alumina, the lanthana-doped alumina comprising 10% by weight or less of lanthana relative to its total weight.

[0016] In another preferred embodiment, the refractory metal oxide support is selected from mixtures or mixed oxides of ceria and alumina having a mass ratio of 10:90 to 90:10.

[0017] In another preferred embodiment, the platinum is pretreated.

[0018] In another preferred embodiment, the three-way catalyst (TWC) further comprises an oxygen storage component (OSC) and / or a promoter component.

[0019] In another preferred embodiment, the three-way catalyst (TWC) has a platinum to palladium weight ratio of less than 1:1.

[0020] A second aspect of the present invention relates to a method of treating an exhaust gas stream from a gasoline engine, the method comprising the steps of providing an exhaust gas stream from the gasoline engine containing oxides of nitrogen (NOx), carbon monoxide (CO) and hydrocarbons (HC), and contacting the exhaust gas stream with a three-way catalyst (TWC) of the present invention.

[0021] A third aspect of the present invention relates to a method of using the three-way catalyst (TWC) of the present invention to purify nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) from the exhaust gas stream of a gasoline engine.

[0022] In a preferred embodiment of the third aspect of the present invention, a method of use of a three-way catalyst (TWC) comprises purifying an exhaust gas stream of a gasoline engine comprising an engine bed temperature in excess of 1000°C.

[0023] As used herein, the terms "catalyst," "catalyst function," "catalyst component," "catalyst material," and the like refer to a material that promotes a reaction or reactions.

[0024] Most importantly, an exhaust gas treatment system must be capable of removing the three major pollutants produced by a typical gasoline engine, including nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO). Thus, removal of these three most important pollutants is accomplished in the present invention by a three-way catalyst (TWC).

[0025] The term "three-way conversion catalyst" (TWC) refers to the function of three-way conversion in which hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) are converted substantially simultaneously. For example, gasoline engines typically operate under near-stoichiometric reaction conditions that oscillate or perturb slightly between fuel-rich and fuel-lean air-fuel ratios (A / F ratios) (λ=1±0.01) with a perturbation frequency of 0.5-2 Hz. As used herein, "stoichiometric" refers to the conditions of a gasoline engine taking into account the oscillation or perturbation of the A / F ratio near stoichiometry. A three-way conversion catalyst (TWC) may include a suitable refractory metal oxide support and, optionally, an oxygen storage component (OSC) having multiple states that allow it to retain and release oxygen under conditions of varying air-fuel ratios. Under rich conditions in which oxides of nitrogen (NOx) are reduced, the oxygen storage component (OSC) provides a small amount of oxygen to consume unreacted carbon monoxide (CO) and hydrocarbons (HC). Similarly, under lean conditions where carbon monoxide (CO) and hydrocarbons (HC) are oxidized, the oxygen storage component (OSC) reacts with excess oxygen and / or NOx, resulting in the conversion of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) all simultaneously (or essentially all simultaneously) even in the presence of an atmosphere that oscillates between fuel-rich and fuel-lean air / fuel ratios. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a diagram of NEDC GSS data for a 1.4L GDI engine trace showing conversion of hydrocarbons, carbon monoxide and nitrogen oxide emissions over model catalysts (1×4″ core) immobilized on various support materials after 4 hours of oven aging at 900° C. (10% steam, 10% O2). [Diagram 2]FIG. 2 shows WLTC tailpipe emissions of hydrocarbons, carbon monoxide and nitrogen oxides (Chasis Dyno 1.4L TGI vehicle) after purification over multi-layer three-way catalysts (same composition and dual coating design of every catalyst with the same PdRh bottom layer, top layer being either Pd / alumina or Pt / alumina) containing various platinum group metals supported on selected support materials after two-stage aging at 850° C. for 50 hours and at 950° C. inlet temperature for 50 hours (900° C. for 50 hours and at 1000° C. bed temperature for 50 hours). [Diagram 3] FIG. 3 compares WLTC tailpipe emissions (2L GDI engine) of hydrocarbons, carbon monoxide and nitrogen oxides after purification over multiple multi-layer three-way catalysts (multi-layer design; Pt on SMSI support; 4.0×5.35″, 900 / 2.5) containing various platinum group metals on various support materials after aging at 980° C. bed temperature for 50 hours. [Figure 4] FIG. 4 compares WLTC tailpipe emissions (2L GDI engine) of hydrocarbons, carbon monoxide and nitrogen oxides after purification over a multi-layer three-way catalyst containing various platinum group metals (multi-layer design; Pt on L-doped alumina support A; PdRh0 / 70 / 10 standard; 4.66×4.5″, 600 / 4) after aging for 101 hours at a bed temperature of 1030° C. [Diagram 5] FIG. 5 compares WLTC tailpipe emissions (2L, GDI engine) of hydrocarbons, carbon monoxide and nitrogen oxides after purification over a three-way catalyst (multi-layer design, Pt on L-doped alumina vs. Pt on ceria-doped alumina; PdRh0 / 72 / 8 standard; 4.66×4.5″, 600 / 4 ceramic substrate) after aging for 100 hours at a bed temperature of 1030° C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The three-way conversion catalysts of the present invention are described in further detail below.

[0028] Thus, a three-way layered catalyst (TWC) comprises a number of essential catalytic components. Preferably, the composition of the three-way conversion catalyst coating comprises a hydrocarbon (HC) oxidizing component, a carbon monoxide (CO) oxidizing component, and a nitrogen oxide (NOx) reducing component, and is selected to enable purging of NOx, HC, and CO from the exhaust gas stream.

[0029] The three-way conversion catalyst of the present invention includes a platinum group metal (PGM) component that is combined in the catalyst with a suitable support material, typically a refractory metal oxide support, the combination of the platinum group metal (PGM) and the refractory metal oxide support being important for achieving high catalytic performance and excellent stability with respect to aging at high temperatures.

[0030] The entire TWC catalyst is arranged on a suitable support material, which is defined in more detail below, that allows the TWC catalyst to be arranged in an optimal manner in the exhaust gas treatment line of the vehicle.

[0031] The three-way conversion catalyst is preferably located downstream of the exhaust gas treatment line, and typically in a close-coupled position. The term "close-coupled" refers to a position in fluid communication with and immediately downstream of the engine outlet, preferably a gasoline engine outlet, preferably within 50 cm, more preferably within 30 cm, and most preferably within 20 cm of the engine outlet. Thus, in the context of the present invention, a "close-coupled" position is understood as generally understood in the art, e.g., a position substantially closer to the engine than a conventional "underfloor" position (under the floor of the vehicle). Generally, but not exclusively, such a "close-coupled" position is preferably in the engine compartment, usually under the hood of the vehicle, and adjacent to the exhaust manifold. Thus, a catalyst located in a "close-coupled" position is generally exposed to hot exhaust gases immediately after the engine has been warmed up, and therefore often serves to reduce hydrocarbon emissions during cold start, which is typically the period immediately after starting the engine from ambient conditions.

[0032] Thus, a preferred three way catalyst (TWC) of the present invention for treating an exhaust gas stream comprising nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) comprises a platinum group metal (PGM), a refractory metal oxide support, and a carrier, wherein the platinum group metal (PGM) comprises platinum, palladium and rhodium, the mass ratio of platinum to palladium in the three way catalyst (TWC) is from 5:95 to 45:55 based on the total mass of the platinum group metals (PGM), and the refractory metal oxide support is selected from a mixture or mixed oxide of ceria and alumina, or a lanthana doped alumina comprising 10 mass% or less of lanthana based on the mass of the refractory metal oxide support, more preferably such a three way catalyst (TWC) is in a close coupled position at the engine outlet.

[0033] Even more preferably, the TWC is in fluid communication with and immediately downstream of the engine outlet, preferably a gasoline engine outlet. Most preferably, the TWC of the present invention is located within 50 cm, more preferably within 30 cm, and most preferably within 20 cm of the engine outlet. It is particularly preferred that the TWC is not in an underfloor location, i.e., under the floor of the vehicle.

[0034] In other words, the TWC is located in a close-coupled position within the engine compartment, preferably under the hood of the vehicle, and adjacent to the exhaust manifold. Thus, TWCs located in a "close-coupled" position are generally exposed to hot exhaust gases immediately after the engine has warmed up, and therefore often serve to reduce hydrocarbon emissions during cold start, which is typically the period immediately after starting the engine from ambient conditions.

[0035] Thus, the present invention relates to an exhaust gas treatment line comprising an engine, preferably a gasoline engine, in combination with the three-way catalyst (TWC) of the present invention, or an exhaust gas treatment line comprising an engine, preferably a gasoline engine, in combination with the three-way catalyst (TWC) of the present invention. In other words, the present invention also relates to an exhaust gas treatment system comprising an engine, preferably a gasoline engine, in combination with the three-way catalyst (TWC) of the present invention. In a preferred embodiment, the exhaust gas treatment system comprising an engine, preferably a gasoline engine, and a three-way catalyst (TWC) has the three-way catalyst, as defined above, in close coupling with the engine outlet of the engine. In other words, the three-way catalyst (TWC) is directly connected to the engine outlet without any additional device or catalyst disposed between the engine outlet and the three-way catalyst (TWC). That is, the three-way catalyst (TWC) of the present invention is in fluid communication with the engine outlet and located immediately downstream of the engine outlet, as described above.

[0036] When a three-way catalyst (TWC) is combined with an additional particulate filter to form a four-way catalyst (FWC) in the exhaust gas treatment line, the four-way catalyst (FWC) is also most preferably positioned "close coupled", as is the three-way catalyst (TWC).

[0037] A variety of different support materials can be used in the three-way catalyst of the present invention, which are discussed in more detail below.

[0038] The three-way catalyst (TWC) preferably further comprises an additional oxygen storage component (OSC) and / or a promoter component.

[0039] The three-way catalyst coating comprises a platinum group metal (PGM) component. It is essential for the present invention that the three-way catalyst (TWC) combines the presence of at least three platinum group metals platinum, palladium and rhodium. Furthermore, additional platinum group metals (PGMs) other than platinum, palladium and rhodium may also be present optionally. For example, further platinum group metals (PGMs), such as ruthenium, osmium and / or iridium, may be optionally present in the three-way catalyst (TWC) of the present invention in addition to platinum, palladium and rhodium, although the loadings of the latter three are essential for the present invention.

[0040] In particular, the inventors have found that it is possible to at least partially replace the usual palladium component in the TWC of the present invention with platinum, and thus, in contrast to conventional TWCs known in the prior art that are mostly based on palladium and rhodium as the platinum group metal (PGM) components, the TWC of the present invention contains palladium and rhodium, but also contains a substantial amount of platinum that partially replaces the palladium component.

[0041] In the three-way catalyst (TWC) of the present invention, the relative mass ratio of platinum / palladium / rhodium to the total mass of platinum group metals (PGM) is preferably 5 / 103 / 10 to 54 / 54 / 10, more preferably 10 / 98 / 10 to 45 / 63 / 10, and even more preferably 25 / 83 / 10 to 35 / 73 / 10. Additionally or alternatively, the mass ratio of platinum to palladium is preferably 5:95 to 50:50, more preferably 15:85 to 45:55, and even more preferably 27:73 to 40:60.

[0042] The total loading of the platinum group metal (PGM) components in the three-way catalyst (TWC) of the present invention contains platinum, palladium and rhodium as essential components. More preferably, the three-way catalyst (TWC) contains the platinum group metal (PGM) components supported on the refractory metal oxide support in an amount of 1 to 200 g / ft 3 More preferably, the range is 20 to 180 g / ft 3and even more preferably in the range of 50 to 150 g / ft 3 and most preferably in the range of 70 to 125 g / ft 3 Generally, one of ordinary skill in the art will be familiar with measuring the loading of platinum group metals (PGMs) on catalyst coatings. For example, XRF (X-ray fluorescence) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) can be used to measure the catalyst loading of platinum group metals (PGMs).

[0043] In a preferred embodiment of the present invention, the platinum component of the three-way catalyst (TWC) can be additionally pretreated. The pretreatment of the platinum component of the present invention refers to the component and / or preparation method, which obtains the pretreated platinum component by impregnating the palladium, or rhodium, and / or any other platinum group metal (PGM) of the present invention on the corresponding refractory metal oxide support, calcining the refractory metal oxide support containing the palladium, or rhodium, or any other platinum group metal (PGM) of the present invention, then impregnating platinum on the calcined refractory metal oxide support containing the palladium, or rhodium, and / or any other platinum group metal (PGM) of the present invention, and calcining the platinum-containing refractory metal oxide support containing the palladium, or rhodium, or any other platinum group metal (PGM) of the present invention.

[0044] The partial replacement of palladium with platinum in the TWC catalyst of the present invention without substantially reducing the catalyst's ability to purge hydrocarbons (HC), nitrogen oxides (NOx) and carbon monoxide (CO) is surprising and unexpected, since platinum is known to exhibit sintering behavior at high engine temperatures, thereby degrading the surface area and overall performance of TWC catalysts. Moreover, this is an important discovery from a commercial standpoint, since platinum is substantially cheaper than palladium.

[0045] The inventors have found that partial replacement of palladium with platinum without substantial loss of catalytic function is particularly achievable when selected platinum group metals (PGMs) of the present invention are combined with selected refractory metal oxide support materials.

[0046] The three-way catalyst (TWC) of the present invention comprises a refractory metal oxide support. The refractory metal oxide support is essential to the present invention and is combined with the platinum group metal (PGM) component in the catalyst of the present invention. Preferably, the refractory metal oxide support is non-zeolitic. There are several particularly preferred refractory metal oxide support materials that can be used in the three-way catalyst (TWC) of the present invention to achieve the claimed technical effects.

[0047] One preferred refractory metal support material comprises a mixture or mixed oxide of cerium oxide and aluminum oxide, preferably having a mass ratio of ceria to alumina of 10:90 to 90:10, or 25:75 to 75:25, or 30:70 to 70:30, more preferably 40:60 to 60:40, and even more preferably 45:55 to 55:45.

[0048] Another preferred refractory metal support material comprises aluminum oxide doped with lanthana (such as La2O3). Lantana-doped alumina refers to alumina containing a small amount of lanthana, preferably 10% by weight or less, more preferably 7% by weight or less, even more preferably 5% by weight or less, and most preferably 4% by weight or less, based on the weight of the lanthana-doped alumina. La-doped alumina (L-doped alumina) contains at least 0.5% by weight, more preferably at least 1% by weight, and most preferably at least 2% by weight of lanthana, based on the weight of the lanthana-doped alumina.

[0049] The aluminum oxide used in the refractory metal oxide support material of the present invention may preferably be a stabilized aluminum oxide. The aluminum oxide of the refractory metal oxide support may preferably be a gamma aluminum oxide. The refractory metal oxide support of the three-way conversion catalyst (TWC) of the present invention may optionally contain additional metal oxides such as zirconia, ceria, baria and / or neodymia.

[0050] The total loading of the refractory metal oxide support in the three-way catalyst (TWC) of the present invention is preferably 0.2 to 6.0 g / in 3 More preferably, the range is 0.5 to 5.0 g / in 3 More preferably, the range is 1.0 to 4.0 g / in 3 and even more preferably in the range of 2.5 to 3.5 g / in 3 The range is.

[0051] The ceria content in the three-way catalyst (TWC) of the present invention is preferably 0.4 to 4.0 g / in 3 More preferably, the range is 0.7 to 3.0 g / in 3 and even more preferably in the range of 0.9 to 2.0 g / in 3 or most preferably in the range of 1.0 to 1.5 g / in 3 The range is.

[0052] More preferably, the refractory metal oxide support has a porosity in the range of 0.05-1.5 ml / g, more preferably in the range of 0.1-1.0 ml / g, more preferably in the range of 0.15-0.8 ml / g. The porosity of the refractory metal oxide support is determined by analysis of the physisorption isotherm via N2 physisorption and BJH (Barett, Joyner, Halenda) analysis according to DIN66134.

[0053] The TWC of the present invention preferably includes an additional oxygen storage compound, which may be present in the bottom washcoat or the top washcoat, or in both the bottom and top washcoats, when multiple washcoats are applied in the TWC of the present invention.

[0054] More preferably, the oxygen storage compound comprises cerium, and even more preferably, comprises one or more of cerium oxide, a mixture of oxides comprising cerium oxide, and a mixed oxide comprising cerium, the mixed oxide comprising cerium preferably additionally comprising one or more of zirconium, yttrium, neodymium, and praseodymium, more preferably additionally comprising one or more of zirconium, yttrium, neodymium, and lanthanum, more preferably additionally comprising zirconium, yttrium, neodymium, and lanthanum. Furthermore, the oxygen storage compound comprising cerium may consist of two or more different mixed oxides, each of which may comprise cerium and one or more of zirconium, yttrium, neodymium, lanthanum, and praseodymium. A mixture or mixed oxide of cerium oxide and zirconium oxide is one preferred oxygen storage component.

[0055] Any oxygen storage compound has a preferred porosity in the range of 0.05-1.5 ml / g, more preferably in the range of 0.1-1.0 ml / g, more preferably in the range of 0.15-0.8 ml / g. The porosity of the oxygen storage compound is determined by physical adsorption of N2 and analysis of the physical adsorption isotherm via BJH (Barett, Joyner, Halenda) analysis according to DIN66134.

[0056] The three-way catalyst (TWC) preferably comprises an additional promoter component. The term "promoter" as used in the context of the present invention relates to a compound which promotes the overall catalytic activity.

[0057] When the three-way conversion catalyst (TWC) of the present invention is a layered catalyst comprising multiple coatings, i.e. multiple washcoats including, for example, a bottom washcoat and a top washcoat, the promoter component may be preferably comprised in either the bottom washcoat or the top washcoat, or even more preferably in both the bottom washcoat and the top washcoat. The promoter component preferably comprises one or more of zirconium, barium, strontium, lanthanum, neodymium, yttrium, and praseodymium. One preferred promoter component is defined by a mixture of barium, zirconium, and neodymium, or a mixed oxide of barium, zirconium, and neodymium. When a ternary mixture of barium oxide, zirconium oxide, and neodymium oxide is used as the promoter component, the mass ratio of barium oxide to zirconium oxide to neodymium oxide is preferably 2:1:1 to 7:1:1, more preferably 3:1:1 to 6:1:1, and even more preferably 4:1:1 to 5:1:1. Another preferred promoter component comprises one or more of zirconium and barium. In one embodiment, the promoter comprises, and more preferably is, one or more of a mixture of barium oxide and strontium oxide, and a mixed oxide of barium and strontium. Another highly preferred promoter is a mixture of barium oxide and zirconium oxide, or either barium oxide or zirconium oxide. When a mixture of barium oxide and zirconium oxide is used as the promoter component, the mass ratio of barium oxide to zirconium oxide is preferably 0.5 to 5, more preferably 1 to 3, and even more preferably 1.2 to 2.5. The preferred amount of promoter component in the three-way catalyst (TWC) of the present invention or in one of the washcoats, such as the bottom washcoat or the top washcoat, is 0.01 to 0.5 g / in 3 , more preferably 0.02 to 0.25 g / in 3 or even more preferably in the range of 0.05 to 0.12 g / in 3 The loading range is defined as:

[0058] In the present invention, it is preferred that the three-way conversion catalyst has a layered design, i.e., the three-way conversion catalyst of the present invention is preferably prepared by applying the various catalytic functions or catalytic components to the support in the form of a coating or multiple coatings (commonly referred to as washcoat(s)).

[0059] As used herein and as described in Heck, Ronald and Robert Farrauto, Catalytic Air Pollution Control, New York: Wiley-Interscience, 2002, pp. 18-19, a washcoat layer comprises a layer of compositionally distinct material disposed on the surface of a monolithic substrate or, optionally, on top of an underlying washcoat layer. Washcoats are typically comprised of a refractory metal oxide support having a high surface area, additional catalytically active materials including platinum group metals (PGMs), and optionally additional materials such as oxygen storage components and / or promoters. Preferably, additives such as binders may also be included.

[0060] Preferably, the three-way catalyst (TWC) is applied at a concentration of 0.5 to 5 g / in, preferably in the form of one or more washcoats. 3 More preferably, in the range of 1.5 to 4.5 g / in 3 More preferably, the range is 2.0 to 4.0 g / in 3 , and most preferably 2.7 to 3.5 g / in 3 The carrier is present at a total loading in the range of 100 to 200 nm.

[0061] The three-way conversion catalyst of the present invention can have one single washcoat layer, but more preferably has two or more washcoat layers, especially two washcoat layers including a bottom washcoat and a top washcoat. Each washcoat layer can have its own chemical catalytic function depending on its exact composition. It is particularly preferred that the bottom washcoat (or first coating) is applied on the substrate, and the top washcoat (or second coating) is applied on the bottom washcoat.

[0062] As far as the bottom washcoat or first washcoat (or first coating) is concerned, a combination of palladium and platinum is preferably added as a platinum group metal (PGM), more preferably in the absence of rhodium. Other platinum group metals, such as ruthenium, osmium and / or iridium, can be optionally present together with palladium and platinum. In a preferred embodiment, the bottom washcoat can include palladium as the only platinum group metal (PGM), in the absence of platinum and rhodium. Alternatively, platinum and palladium are combined in the bottom washcoat in the absence of any other platinum group metals (PGM).

[0063] Optionally, palladium can be combined in the bottom washcoat with other platinum group metals (PGMs), such as ruthenium, osmium and / or iridium, in the absence of platinum and rhodium.

[0064] The platinum group metal (PGM) component of the bottom washcoat is supported on a refractory metal oxide support. Preferably, the refractory metal oxide support of the bottom washcoat is non-zeolitic. The refractory metal oxide support of the bottom washcoat preferably comprises a mixture of aluminum oxide and cerium oxide. Another preferred refractory metal support material of the bottom washcoat comprises lanthanum doped aluminum oxide. The aluminum oxide used in the refractory metal oxide support material may preferably be stabilized aluminum oxide. The aluminum oxide of the refractory metal oxide support of the bottom washcoat may also preferably be gamma aluminum oxide. The refractory metal oxide support of the bottom washcoat may optionally comprise additional metal oxides such as zirconia, ceria, baria and / or neodymia.

[0065] Another preferred refractory metal support material for the bottom washcoat comprises a mixture or mixed oxide of cerium oxide and aluminum oxide. Preferably, the mixture or mixed oxide of ceria and alumina has a weight ratio of ceria to alumina of 10:90 to 90:10, 25:75 to 75:25, or 30:70 to 70:30, more preferably 40:60 to 60:40, and even more preferably 45:55 to 55:45.

[0066] Another preferred refractory metal support material of the bottom washcoat comprises aluminum oxide doped with lanthana (such as La2O3). Lantana-doped alumina refers to alumina containing a small amount of lanthana, preferably 10% by weight or less, more preferably 7% by weight or less, even more preferably 5% by weight or less, and most preferably 4% by weight or less, based on the total weight of the lanthana-doped alumina. La-doped alumina (L-doped alumina) contains at least 0.5% by weight, more preferably at least 1% by weight, and most preferably at least 2% by weight of lanthana, based on the total weight of the lanthana-doped alumina.

[0067] The aluminum oxide used in the refractory metal oxide support material of the bottom washcoat can preferably be stabilized aluminum oxide. The aluminum oxide of the refractory metal oxide support can also preferably be gamma aluminum oxide. The refractory metal oxide support of the three-way conversion catalyst of the present invention can optionally contain additional metal oxides such as zirconia, ceria, baria and / or neodymia.

[0068] As far as the top washcoat or second washcoat (or second coating) is concerned, a combination of rhodium and palladium is preferably added as a platinum group metal (PGM), more preferably in the absence of platinum. Other platinum group metals, such as ruthenium, osmium and / or iridium, can be optionally present together with rhodium and palladium. In a preferred embodiment, the top washcoat can even contain rhodium as the only platinum group metal (PGM), in the absence of platinum and palladium. In another preferred embodiment, the top washcoat includes rhodium, palladium and platinum. Optionally, rhodium can be combined in the topcoat with other platinum group metals (PGM), such as ruthenium, osmium and / or iridium, in the absence of platinum and palladium.

[0069] The platinum group metal (PGM) component of the top washcoat is supported on a refractory metal oxide support. Preferably, the refractory metal oxide support of the top washcoat is non-zeolitic. The refractory metal oxide support of the top washcoat preferably comprises a mixture of aluminum oxide and cerium oxide. Another preferred refractory metal support material of the top washcoat comprises lanthanum doped aluminum oxide. The aluminum oxide used in the refractory metal oxide support material may preferably be stabilized aluminum oxide. The aluminum oxide of the refractory metal oxide support of the top washcoat may also preferably be gamma aluminum oxide. The refractory metal oxide support of the top washcoat of the present invention may optionally comprise additional metal oxides such as zirconia, ceria, baria and / or neodymia.

[0070] One preferred refractory metal support material for the top washcoat comprises a mixture or mixed oxide of cerium oxide and aluminum oxide, preferably having a mass ratio of ceria to alumina of 10:90 to 90:10, 30:70 to 70:30, more preferably 40:60 to 60:40, and even more preferably 45:55 to 55:45.

[0071] Another preferred refractory metal support material of the top washcoat comprises lanthanum-doped aluminum oxide, such as lanthana (e.g., La2O3). Lantana-doped alumina refers to alumina containing a small amount of lanthana, preferably 10% by weight or less, more preferably 7% by weight or less, even more preferably 5% by weight or less, and most preferably 4% by weight or less, based on the weight of the lanthana-doped alumina. La-doped alumina contains at least 0.5% by weight, more preferably at least 1% by weight, and most preferably at least 2% by weight of lanthana, based on the weight of the lanthana-doped alumina.

[0072] The aluminum oxide used in the refractory metal oxide support material may preferably be a stabilized aluminum oxide. The aluminum oxide of the refractory metal oxide support may also preferably be a gamma aluminum oxide. The refractory metal oxide support of the three-way conversion catalyst (TWC) of the present invention may optionally contain additional metal oxides such as zirconia, ceria, baria and / or neodymia.

[0073] In view of stringent emission regulations on particulate matter such as Euro 6c, the removal of particulate matter from combustion engines has become an important requirement in the treatment of exhaust gas streams. Therefore, the three-way catalyst (TWC) of the present invention can be combined with a particulate filter, for example a gasoline particulate filter (GPF) used to purify the exhaust stream of a gasoline engine. When a three-way catalyst (TWC) is combined with an additional particulate filter function, the resulting catalyst is typically defined as a so-called "four-way catalyst" (FWC).

[0074] As used herein, the term "particulate filter" refers to a substrate sized and configured to trap particulates generated in the exhaust gas stream, preferably from a gasoline engine. Particulate matter can be trapped, for example, by using a particulate (or soot) filter, by using a flow-through substrate with an internal serpentine path that changes the direction of flow of the particulates to cause them to fall out of the exhaust stream, by using a metal substrate such as a corrugated metal carrier, or by other methods known to those skilled in the art. Suitable substrates are described in more detail below, but other filter devices are also suitable, for example a pipe with a roughened surface that can knock particulates out of the exhaust stream. A pipe with bends may also be suitable.

[0075] When the TWC of the present invention is combined with a particulate filter component, there are several options for further removing particulate matter from the exhaust gas flow. One preferred option for including particulate removal function in the TWC is to add a separate particulate filter that is not coated with additional catalytic functions. As an example, such a bare particulate filter is not coated with the TWC or any other catalytic functions other than the filter function that can purge particulate matter from the exhaust gas flow. The initial particulate removal function included an uncoated gasoline particulate filter (GPF) located downstream of the TWC. Another preferred option for the particulate filter function is a particulate filter coated with the TWC of the present invention. In other words, the particulate filter is a coated particulate filter. In this embodiment, the particulate filter is used as a substrate with the TWC of the present invention coated on the surface or pores of the particulate filter. As further detailed above, the three-way catalyst (TWC), when present on the particulate filter, can be present in the form of one single washcoat or multiple washcoats (including, for example, two different washcoats or coatings, i.e., a top washcoat and a bottom washcoat). The coating of the particulate filter can be present in various ways. One option is to present the three-way catalyst (TWC) on the filter substrate by a so-called "in-wall coating". Another option is to combine such an in-wall coating with an additional "on-wall coating" on the wall-flow filter substrate.

[0076] The three-way conversion catalyst (TWC) of the present invention is disposed on a suitable substrate (or support). A suitable substrate is three-dimensional, having a length, diameter and volume like a cylinder. The shape does not necessarily have to conform to a cylinder. The length is the axial length defined by the inlet and outlet ends. The substrate of the present invention may be constructed of any material typically used in the preparation of automotive catalysts, and typically includes a metal or ceramic honeycomb structure. Preferably, the substrate provides a plurality of wall surfaces onto which the washcoat composition(s) are applied and adhere, thereby serving as a substrate for the catalyst composition.

[0077] The substrate can be constructed of any material typically used in the preparation of automotive catalysts, and typically includes a metal or ceramic honeycomb structure. The substrate typically provides a plurality of walls to which the washcoat composition is applied and adheres, thereby acting as a substrate for the catalyst composition.

[0078] The substrate for the three-way conversion catalyst of the present invention may be a typical monolith substrate of the type having fine, parallel gas flow passages extending from the inlet or outlet face of the substrate such that the passages are open to the flow of fluid therethrough ("flow-through substrate").

[0079] The flow-through substrate can be a monolithic substrate, including a flow-through honeycomb monolithic substrate. Those skilled in the art are familiar with flow-through substrates, which generally have fine, parallel gas flow passages extending from the inlet end to the outlet end of the substrate, the passages being open to the flowing fluid. A passage is essentially a straight path from its fluid inlet to its fluid outlet, and is defined by a wall on which a catalytic coating can be placed so that gas flowing through the passage contacts the catalytic material. The flow paths of the flow-through substrate are thin-walled channels, which can be of any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. The flow-through substrate can be made of ceramic or metal, as described further below. The flow-through substrate can be, for example, about 50 in 3 ~About 1200in3 , a cell density (inlet opening) of about 300 to about 600 cpsi, or ...

[0080] Suitable substrates can be ceramic substrates made of any suitable refractory material, such as cordierite, cordierite-α-alumina, aluminum titanate, silicon titanate, silicon carbide, silicon nitride, zircon mullite, spodumene, alumina-silica-magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, α-alumina, aluminosilicate, and the like.

[0081] Substrates suitable in the present invention may also be metals, including one or more metals or metal alloys. Metal substrates may include any metal substrate, such as those having openings or "cutouts" in the channel walls. Metal substrates may be used in a variety of shapes, such as pellets, corrugated sheets, or monolith forms. Specific examples of metal substrates include heat-resistant base metal alloys, particularly those in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium, and aluminum, the sum of which may advantageously comprise at least about 15% by weight of the alloy, for example, about 10-25% by weight chromium, about 1-8% by weight aluminum, and about 0-20% by weight nickel, in each case based on the weight of the substrate. Examples of metal substrates include those with straight channels, those with blades protruding along the axial channels to disrupt the gas flow and open gas flow communication between the channels.

[0082] The most preferred substrate in the present invention is a wall-flow filter substrate.Wall-flow filter substrate, as understood by those skilled in the art, has a plurality of fine and substantially parallel gas flow passages extending along the longitudinal axis of the substrate, typically each passage is blocked at one end of the substrate body, and alternating passages are blocked at the opposite end face ("wall-flow filter").Suitable flow-through and wall-flow substrates are also taught, for example, in International Publication No. WO2016 / 070090, the entirety of which is incorporated herein by reference.

[0083] The three-way conversion catalysts of the present invention are preferably prepared by applying the various catalytic functions or components to a substrate in the form of a coating or multiple coatings to form a layered catalyst (commonly referred to as a washcoat(s)).

[0084] For example, the washcoat layer of a composition containing the catalytic components of a three-way conversion catalyst (TWC) can be formed by preparing a mixture or solution of platinum group metal (PGM) precursors selected from platinum, palladium and / or rhodium, optionally some additional precious metal group elements, in a suitable solvent, such as water. Generally, from the standpoint of economic and environmental aspects, aqueous solutions of soluble compounds or complexes of platinum group metals, including platinum, palladium and / or rhodium, are preferred. Typically, the platinum group metal precursors are utilized in the form of a compound or complex to achieve dispersion of the precursor on the support. For purposes of the present invention, the term "platinum group metal precursor" refers to any compound, complex or analog that decomposes or converts to a catalytically active form during calcination or an early stage of its use. Suitable complexes or compounds preferably include, but are not limited to, platinum chloride (e.g., [PtCl4] 2- , [PtCl6] 2- salts), platinum hydroxides (e.g. [Pt(OH)6] 2- salts), platinum amines (e.g. [Pt(NH3)4] 2+ , Pt(NH3)4] 4+ salts), platinum hydrates (e.g. [Pt(OH2)4] 2+For platinum, these include platinum bis(acetylacetonate), platinum bis(acetylacetonate), and mixed compounds or complexes (e.g., [Pt(NH3)2(Cl)2]). A representative commercially available source of platinum is 99% ammonium hexachloroplatinate from Strem Chemicals Inc., which may contain trace amounts of other platinum group metals (PGMs).

[0085] However, it will be understood that the present invention is not limited to a particular type, composition, or purity of platinum precursor. Similar platinum precursors can be applied. Furthermore, as far as palladium and rhodium are concerned, those skilled in the art will be familiar with similar palladium and rhodium group metal (PGM) precursors that can be applied like the platinum precursors described above.

[0086] A mixture or solution of platinum group metal (PGM) precursors is added to the support by one of several chemical means. This includes impregnating the support with a solution of the precursors, which may be followed by a fixation step incorporating an acidic (e.g., acetic acid) or basic (e.g., ammonium hydroxide) component. This wet solid can be chemically reduced or calcined, or used as is. Alternatively, the support may be suspended in a suitable medium (e.g., water) and reacted with the precursor in solution. Additional processing steps may include fixation with an acidic (e.g., acetic acid) or basic (e.g., ammonium hydroxide), chemical reduction, or calcination. In the impregnation process, an appropriate amount of an optional oxygen storage component (OSC) and / or promoter, and other additives, if desired, may be added to the slurry for impregnation of the substrate.

[0087] As already indicated above, the platinum component can be pretreated during the formation of the corresponding washcoat layer.

[0088] To apply the TWC (e.g., a washcoat layer therefrom), finely divided particles of the TWC are suspended in a suitable medium, such as water, to form a slurry. Other promoters and / or stabilizers and / or surfactants may be added to the slurry as a mixture or solution in water or a water-miscible medium. In one or more embodiments, the slurry is milled to result in substantially all solids having a particle size less than about 10 microns in average diameter, i.e., in the range of about 0.1 to 8 microns. The milling may be performed in a ball mill, continuous Eiger mill, or other similar equipment. In one or more embodiments, the suspension or slurry has a pH of about 2 to less than about 7. The pH of the slurry may be adjusted as needed by adding a suitable amount of inorganic or organic acid to the slurry. The solids content of the slurry may be, for example, about 20 to 60% by weight, and more specifically, about 35 to 45% by weight. The substrate may then be dipped into the slurry or the slurry may be coated onto the substrate to deposit a desired loading of the TWC layer on the substrate. The coated substrate is then dried at about 100° C. and calcined, for example, by heating at 300-650° C. for about 1 to about 3 hours. Drying and calcining are typically performed in air. The coating, drying and calcining process may be repeated as necessary to achieve a final desired weight of the TWC (e.g., washcoat layer therefrom) on the substrate. In some cases, complete removal of the liquid and other volatile components may not occur until the TWC is placed into service and subjected to the high temperatures encountered during operation.

[0089] After calcination, the three-way catalyst (washcoat) loading can be determined by calculating the difference between the coated and uncoated mass of the substrate. As will be apparent to those skilled in the art, the three-way catalyst (TWC) loading can be varied by varying the solids content and slurry viscosity of the coating slurry. Alternatively, the substrate can be repeatedly immersed in the coating slurry, followed by removal of excess slurry as described above.

[0090] The present invention also relates to a method of treating an exhaust gas stream, preferably from a gasoline engine, comprising the steps of providing an exhaust gas stream, preferably from a gasoline engine, containing nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC), and contacting the exhaust gas stream with a three-way catalyst (TWC) of the present invention.

[0091] The present invention also relates to a method of using the three-way catalyst (TWC) of the present invention to purify nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) from an exhaust gas stream, preferably produced from a gasoline engine.

[0092] In a preferred embodiment, the method of using a three-way catalyst (TWC) to purify an exhaust gas stream from a gasoline engine involves an engine bed temperature in excess of 1000°C, more preferably in excess of 1020°C.

[0093] In the present invention, it is shown that the three-way catalyst (TWC) of the present invention can provide excellent stability and purification performance under typical aging conditions resulting from subjecting the TWC to a typical engine bed temperature of about 1000°C.

[0094] This result has been achieved by the three-way catalyst (TWC) of the present invention, which includes a combination of the three platinum group metals (PGMs): platinum, palladium and rhodium. In view of the three-way catalysts (TWC) known from the prior art, palladium has been successfully replaced by platinum to a large extent. Indeed, in the preferred layered three-way catalyst (TWC) of the present invention, a substantial amount of platinum can be used as an additional platinum group metal (PGM) component, which helps to reduce the amount of other platinum group metals (PGMs) that may be more expensive than platinum. In a preferred embodiment, platinum can be used to replace a substantial amount of palladium in the bottom washcoat to form a bottom washcoat that includes a mixture of palladium and platinum as the platinum group metal (PGM) components. Alternatively, or additionally, the top washcoat of the three-way catalyst (TWC) of the present invention can include a combination of palladium and rhodium, or even a ternary combination of platinum, palladium and rhodium.

[0095] In the present invention, it has been found that the stability of the platinum-containing three-way catalyst (TWC) of the present invention against aging at high temperature is unexpectedly improved by the platinum-containing platinum group metal (PGM) component. Furthermore, when a selected refractory metal oxide support, most preferably a mixture or mixed oxide of ceria-alumina or lanthanum-doped alumina, is additionally used, the stability of the three-way catalyst (TWC) against aging is improved. By this approach, the reduction of the emissions of nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) is at least maintained or even reduced compared to three-way catalysts (TWC) in which platinum is essentially avoided or at least reduced in order to maintain the catalytic performance under aging. It is particularly noteworthy that the performance of the three-way catalyst of the present invention can be maintained even at very high engine aging temperatures above 1000°C, for example at bed temperatures above 1020°C.

[0096] Further preferred embodiments of the present invention are as follows.

[0097] Further preferred embodiment 1: 1. A three way catalyst (TWC) for treating an exhaust gas stream containing oxides of nitrogen (NOx), carbon monoxide (CO) and hydrocarbons (HC), comprising a platinum group metal (PGM), a refractory metal oxide support, and a carrier, wherein the platinum group metal (PGM) comprises platinum, palladium and rhodium, the mass ratio of platinum to palladium in the three way catalyst (TWC) being from 5:95 to 45:55 based on the total mass of the platinum group metal (PGM), and the refractory metal oxide support is selected from a mixture or mixed oxide of ceria and alumina, or a lanthana doped alumina containing 10% by mass or less of lanthana based on the mass of the refractory metal oxide support.

[0098] Further preferred embodiment 2: A three-way catalyst (TWC) for treating an exhaust gas stream according to a preferred embodiment 1, wherein the three-way catalyst is in a close-coupled position at the engine outlet.

[0099] Further preferred embodiment 3: A three-way catalyst (TWC) for treating an exhaust gas stream according to preferred embodiment 1 or 2, wherein the three-way catalyst is in fluid communication with and immediately downstream of an engine outlet, preferably a gasoline engine outlet.

[0100] Further preferred embodiment 4: A three-way catalyst (TWC) for treating an exhaust gas stream according to any one of preferred embodiments 1 to 3, wherein the three-way catalyst is located within 50 cm, more preferably within 30 cm, and most preferably within 20 cm of the engine outlet.

[0101] Further preferred embodiment 5: A three-way catalyst (TWC) for treating an exhaust gas stream according to any one of the preferred embodiments 1 to 4, wherein the three-way catalyst is in an under-floor position, i.e. not under the floor of the vehicle.

[0102] Further preferred embodiment 6: A three-way conversion catalyst (TWC) for treating an exhaust gas stream according to any one of the preferred embodiments 1 to 5, wherein the three-way conversion catalyst is in a close-coupled position within the engine compartment, preferably under the hood of the vehicle, and adjacent to the exhaust manifold.

[0103] Thus, catalysts located in a "close coupled" position are generally exposed to the hot exhaust gases immediately after exiting the engine after the engine has warmed up, and therefore often serve to reduce hydrocarbon emissions during cold start, which is typically the period immediately after starting the engine from ambient conditions.

[0104] Further preferred embodiment 7: An exhaust gas treatment system comprising an engine and a three-way catalyst (TWC) according to any one of preferred embodiments 1 to 6, the three-way catalyst (TWC) being in close coupling position at the engine outlet of the engine. EXAMPLES

[0105] Description of catalyst preparation Example 1 / Figure 1: Pd or Pt on alumina or support A, 112 g / ft 3 (Model catalyst) This technology delivers Pd or Pt impregnated onto highly porous alumina with a total washcoat loading of 1.53 g / in in a single slurry layer design. 3 The main component of the slurry was highly porous alumina, which was impregnated with Pd from an aqueous solution of palladium nitrate to give a final dry Pd content of 112 g / ft 3 In this process, alumina was impregnated with Pd, and then the alumina-PGM frit (60–75% solids) was heat-set at 400–600 °C for 2–4 h.

[0106] The calcined PGM-containing frits were slurried with distilled water and a surfactant such as n-octanol under constant stirring. The slurry solids were adjusted (35-40%) to improve pH and viscosity measurements and wet-milling. After milling, the pH was adjusted (3.2-4.5) with nitric acid. The slurry particle size distribution (D90) was also measured before and after milling (12-17 μm).

[0107] Ceramic honeycomb flow-through substrate cores (1×4″, 600 / 4) were each coated, dried (120-180° C.) and fired (400-600° C.) in air. Both Pd and Pt on Support A (ceria-alumina 50 / 50) were prepared similar to the process steps described above.

[0108] Example 2 / Figure 2: 3.5 g / in 3 Washcoat, 0 / 112 / 8 or 56 / 56 / 8 Pt / Pd / Rh full size catalyst, 120g / ft 3 This technology involves a two-layer design with Pd and Rh in the bottom layer, prepared by impregnating Pd and / or Rh onto a particular support (which can be either ceria-zirconia, alumina, or both) and then heat setting the PGM-containing frit at high solids (60-75%) in a 400-600°C kiln for 2-4 hours.

[0109] A slurry was prepared by stirring the sintered frit in a vessel previously filled with distilled water and n-octanol. Accelerators such as barium and lanthanum (acetate or nitrate precursors) were added with thorough mixing. The slurry solids content was set at 35-40% to allow for pH, viscosity measurements and wet milling. After adjusting the initial pH with nitric acid (3.2-4.5), the slurry was milled to the desired particle size (D90 12-17 μm) and then the final pH was adjusted.

[0110] Slurry coating onto ceramic substrates (4.66 x 4" 600 / 4) was performed with drying (120-180 °C) and calcination (400-600 °C) in air, respectively. Top layers containing Pd or Pt on high porosity alumina were prepared by a similar impregnation, heat setting, and slurry process. The latter was coated onto the dried / calcined bottom layer to the desired washcoat loading, followed by drying and a final calcination. Total WC ranged from 2.8 to 4.5 g / in. 3 (BC and TC).

[0111] Example 3 / Figure 3: Pt / Pd / Rh full size 0 / 45 / 10 or 22.5 / 22.5 / 10, 55g / ft 3 This technology also contained a bilayer design, but with a PtPd bottom layer prepared by wet impregnation of Pd and / or Pt onto a particular support (which could be either ceria-zirconia, doped alumina, or both). Following the impregnation step, the PGM-containing frit was heat set at high solids (60-75%) in a 400-600 °C kiln for 2-4 hours.

[0112] A slurry was prepared by stirring the calcined frit in a vessel previously containing distilled water and n-octanol. The other catalyst material components, such as barium, lanthanum and zirconium (acetate or nitrate or sulfate precursors), were added with thorough mixing. The slurry solids content was set at 35-40% to allow for pH, viscosity measurements and wet milling. After adjusting the initial pH with nitric acid (3.2-4.5), the slurry was milled to the desired particle size (D90 12-17 μm) and then the final pH was adjusted.

[0113] Slurry coating onto ceramic honeycomb substrates (4.0 x 5.36", 900 / 2.5) was performed by coating in air, drying (120-180 °C), and firing (400-600 °C), respectively. Pd- and Rh-containing top layers using suitable supports (ceria-zirconia and / or L-doped alumina) were prepared by a similar impregnation, heat setting, and slurry process. The latter was coated onto the dried / fired bottom layer to the desired washcoat loading, followed by drying and firing. Total WC was 2.8-4.5 g / in. 3 (BC and TC).

[0114] Comparative Example A used Pt on Support A (La-doped alumina) and Comparative Example B used Pt on Support B (ceria-doped alumina).

[0115] Example 4 / Figure 4: Pt / Pd / Rh full size of 0 / 70 / 10 or X / 70 to X / 10 (X=Pt), 80g / ft 3 The slurry process and PGM distribution of each layer in Example 4 were the same as in Example 3. However, there were differences due to the washcoat thickness and total PGM loading, and the type and amount of ceria-zirconia (composition), doped alumina, and other material components in each layer. In addition, only one Pt support material (Support A is L-doped alumina) was used in this technique.

[0116] Example 5 / Figure 5: Pt / Pd / Rh full size of 0 / 72 / 8 or X / 72-X / 8 (X=Pt), 80g / ft 3 The slurry process and PGM distribution of each layer for Example 5 was the same as for Example 4. The main difference was the different Pt support in each layer of the trimetallic compared to the standard PdRh. The reference and inventive examples contained the same washcoat loadings in the bottom and top coats, respectively.

[0117] Catalyst performance evaluation The catalyst described in Example 1 was washcoated onto a 1×4″ flow-through ceramic substrate core (400 / 4; CPSI / wt).

[0118] Oven aging was performed in an in-house oven equipped with multiple gas lines to simultaneously deliver multiple gases under controlled flow conditions. All catalysts were aged together in hot water (10% O2 and 10% water vapor) at 900°C in an oven for 4 hours.

[0119] Fuel cut ageing was performed using monolith cans arranged in a five-legged trivet and mounted as close as possible to the CC1 position on a gasoline engine bench. A thermocouple was placed at the engine outlet position and all cans were fitted with a bed TC as well as the tailpipe position. Upstream (engine outlet) and downstream (tailpipe) lambda sensors ensured strict enforcement of the lean / rich conditions of the ageing cycle.

[0120] An individual evaluation of every aged core was performed using a Gasoline System Simulator (GSS) reactor operated using the NEDC test cycle implemented from a full-scale vehicle in CNG mode. To evaluate the impact of hydrothermal aging on the different technologies, the same cores were evaluated in the same reactor in the fresh state before oven aging.

[0121] Fuel cut ageing was performed using a monolith canister arranged in a five-legged trivet and mounted as close as possible to the CC1 position on a gasoline engine bench. A thermocouple was placed at the engine outlet position and all canisters were fitted with a TC in the bed as well as at the tailpipe position. Upstream (engine outlet) and downstream (tailpipe) lambda sensors ensured strict enforcement of the lean / rich conditions of the ageing cycle.

[0122] Dynamic tests (WLTC) were performed on a gasoline engine calibrated for Euro 6. The aged monolith and can monolith were evaluated in the CC1 position according to the Lambda 1 application standard, and lean / rich conditions and temperatures were monitored at the pre (inlet) and post (outlet) positions in the exhaust line.

Claims

1. A three-way catalyst (TWC) for treating an exhaust gas stream containing oxides of nitrogen (NOx), carbon monoxide (CO) and hydrocarbons (HC), the three-way catalyst (TWC) comprising a platinum group metal (PGM), a refractory metal oxide support, and a carrier, the platinum group metal (PGM) comprising platinum, palladium and rhodium.

2. The three-way catalyst (TWC) of claim 1 , wherein the TWC is in a close-coupled position.

3. 3. The three-way catalyst (TWC) of claim 1 or 2, wherein the TWC comprises a plurality of washcoat layers including a bottom washcoat layer and a top washcoat layer.

4. The three-way conversion catalyst (TWC) of claim 3 , wherein the plurality of washcoat layers comprises two washcoat layers, one bottom washcoat layer and one top washcoat layer.

5. 4. The three-way catalyst (TWC) of claim 3, wherein the bottom washcoat layer comprises a combination of platinum and palladium as platinum group metals (PGMs).

6. 4. The three-way catalyst (TWC) of claim 3, wherein the top washcoat comprises a combination of palladium and rhodium as platinum group metals (PGMs).

7. 4. The three-way catalyst (TWC) of claim 3, wherein the bottom washcoat layer comprises platinum and palladium as the only platinum group metals (PGMs) and / or the top washcoat layer comprises rhodium as the only platinum group metals (PGMs), preferably palladium and rhodium, and more preferably platinum, palladium and rhodium.

8. 3. A three-way catalyst (TWC) according to claim 1 or 2, wherein the refractory metal oxide support is selected from a mixture or mixed oxide of ceria and alumina, or a lanthana-doped alumina containing lanthana in an amount of 10% by weight or less based on the weight of the lanthana-doped alumina.

9. 9. The three-way catalyst (TWC) of claim 8, wherein the refractory metal oxide support is selected from mixtures or mixed oxides of ceria and alumina having a mass ratio of 10:90 to 90:

10.

10. 3. The three-way catalyst (TWC) of claim 1 or 2, wherein the platinum is pretreated.

11. 3. The three-way catalyst (TWC) of claim 1 or 2, further comprising an oxygen storage component (OSC) and / or a promoter.

12. 3. A three-way conversion catalyst (TWC) according to claim 1 or 2, having a platinum to palladium weight ratio of less than 1:

1.

13. 3. A method for treating an exhaust gas stream from a gasoline engine, comprising the steps of providing an exhaust gas stream from the gasoline engine containing nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC), and contacting the exhaust gas stream with a three-way catalyst (TWC) according to claim 1 or 2.

14. 3. Use of a three-way catalyst (TWC) according to claim 1 or 2 for purifying nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) from the exhaust gas stream of a gasoline engine.

15. 15. A method of use of a three-way catalyst (TWC) according to claim 14, comprising purifying the exhaust gas stream of a gasoline engine having an engine bed temperature of above 1000°C, preferably above 1020°C.

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