Ammonia oxidation catalyst with partitioned SCR inlet and PGM outlet for gasoline applications

Abstract

The present invention relates to an exhaust gas treatment system for reducing ammonia emissions from a gasoline engine, the exhaust gas treatment system comprising a three-way conversion catalyst (TWC) and a gasoline particulate filter (GPF), and further comprising a catalytic functional system for reducing tail pipe ammonia emissions, wherein the catalytic functional system for reducing tail pipe ammonia emissions comprises at least a combination of a selective catalytic reduction catalyst (SCR) and an ammoxidation catalyst (AM Ox). The invention also relates to a method for preparing the exhaust gas treatment system and to a method for treating an exhaust gas stream from a gasoline engine using the exhaust gas treatment system of the invention.

Description

[0001] The present invention relates to the field of exhaust gas treatment systems for automotive applications, in particular exhaust gas treatment systems suitable for gasoline engines. In particular, the present invention relates to catalysts and methods for removing ammonia emissions from exhaust streams generated by gasoline engines.

[0002] The EURO 6 regulation requires the removal of nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO) from the exhaust stream of automotive engines. In addition, a reduction in particulate emissions also needs to be achieved.

[0003] These requirements have been met by the introduction of three-way conversion catalysts (TWCs) that can effectively remove nitrogen oxides, hydrocarbons and carbon monoxide, while three-way conversion catalysts (TWCs) optionally combined with filtering functional systems, such as four-way conversion catalysts (FWCs), have been further developed for effective particulate removal.

[0004] Therefore, three-way conversion catalysts (TWC) and four-way conversion catalysts (FWC) have been widely used to treat exhaust gas streams generated in the automotive sector. This applies to exhaust gas streams obtained from diesel engines as well as gasoline engines.

[0005] However, the political drive to achieve climate neutrality, based on the zero-pollution goal of the European Green Deal, will push emissions regulations further. Tighter EURO 7 emission standards are currently being developed, which will require further development of exhaust gas treatment systems in the automotive sector.

[0006] For example, removing ammonia (NH3) from tailpipe emissions will become another mandatory requirement for exhaust gas treatment systems in the near future.

[0007] In this regard, one unresolved problem with currently used exhaust gas treatment lines comes from the potential "ammonia slip" of SCR catalysts in which ammonia injection is used to purify NOx. Moreover, even in exhaust gas treatment systems without an ammonia injection system, ammonia can be formed in the exhaust gas of gasoline engines through several pathways when hydrogen reacts with several nitrogen oxides to form ammonia. Hydrogen is generated at precious metal sites during the so-called water-gas shift reaction, which is promoted by periodic exhaust gas treatment, as is the case in gasoline applications. This pathway includes the reaction of carbon monoxide with water vapor and / or steam reforming at temperatures above 350°C, when hydrocarbons react with water to form hydrogen. For example, nitric oxide (NO) and nitrogen dioxide (NO2) can react in the presence of hydrogen to form ammonia.

[0008] The amount of ammonia formed in the exhaust gas can depend on engine calibration and catalyst composition. The effective concentrations of carbon monoxide and hydrogen in the exhaust stream, the duration of the rich transient, the air / fuel ratio, temperature, and space velocity are all factors that can contribute to ammonia formation. Furthermore, the interaction between platinum group metals (PGMs) and oxygen storage components (OSCs) can also influence hydrogen formation in the water-gas shift reaction.

[0009] Therefore, based on the expected future EURO 7 regulations and the conventional, currently used three-way conversion catalysts (TWC) with a filter function system, existing exhaust gas treatment systems need to be equipped with an additional ammonia purification function in order to significantly reduce ammonia tailpipe emissions from vehicles in the future.

[0010] An additional important objective is to establish a good balance in a conventional three-way conversion catalyst with a particulate filter function system in the presence of an additional ammonia removal function, so as to achieve a synergistic removal of all relevant pollutants, including nitrogen oxides (NOx), unburned hydrocarbons (HC), carbon monoxide (CO), particulates and ammonia (NH3).

[0011] An additional objective of the catalytic configuration is the stability of the exhaust gas treatment system over time during prolonged operation at high temperatures, such operation being typically observed in gasoline engines with alternating lean / rich cycles and relatively high engine temperatures. Therefore, aging stability during prolonged operation at high engine temperatures is a key requirement for any catalytic configuration to be used in an exhaust gas treatment system for a gasoline engine. A further objective is to achieve removal of the relevant pollutants with a catalytic configuration that applies all necessary catalytic functional systems only in amounts not exceeding those absolutely required. Most catalytic functional systems include expensive components, such as platinum group metals or zeolites, which require laborious preparation, leading to the challenge of using only limited amounts of such expensive components in the relevant catalysts.

[0012] These objectives are achieved by a first aspect of the present invention, which is an exhaust gas treatment system for reducing ammonia emissions from a gasoline engine, comprising a three-way conversion catalyst (TWC) and a gasoline particulate filter (GPF), and also comprising a catalytic functional system for reducing tailpipe ammonia emissions, characterized in that the catalytic functional system for reducing tailpipe ammonia emissions comprises at least a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx).

[0013] In a preferred embodiment, the three-way conversion catalyst (TWC) comprises a first three-way conversion catalyst (TWC) followed by a gasoline particulate filter (GPF) coated with a second three-way conversion catalyst (TWC).

[0014] In another preferred embodiment, the three-way conversion catalyst and the gasoline particulate filter (GPF) are located upstream of the exhaust gas treatment system, in a close-coupled (CC) position to the gasoline engine.

[0015] In another preferred embodiment, the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined in a single layer on the substrate.

[0016] In another preferred embodiment, the ammonia oxidation catalyst (AMOx) comprises at least one catalytic metal on an alumina substrate.

[0017] In another preferred embodiment, the ammonia oxidation catalyst (AMOx) comprises at least rhodium on a zirconium oxide-doped alumina support, preferably rhodium in combination with platinum and / or palladium on an alumina support.

[0018] In another preferred embodiment, the ammonia oxidation catalyst (AMOx) does not contain any rhodium.

[0019] In another preferred embodiment, the ammonia oxidation catalyst (AMOx) comprises titanium and / or manganese on an alumina support, preferably in combination with platinum and / or palladium.

[0020] In another preferred embodiment, the selective catalytic reduction catalyst (SCR) comprises a metal-promoted, preferably copper- or iron-promoted zeolite, more preferably copper- or iron-promoted chabazite.

[0021] In another preferred embodiment, the ammonia oxidation catalyst (AMOx) comprises a three-way conversion catalyst (TWC) comprising at least one platinum group metal, an oxygen storage component (OSC) (preferably comprising ceria-zirconia) and optionally a promoter (preferably comprising baria).

[0022] In another preferred embodiment, the catalytic functional system for reducing tailpipe ammonia emissions, which includes at least a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx), is a zoned catalytic functional system defined by a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx), the selective catalytic reduction catalyst comprising a metal-promoted zeolite carrier-coated at the inlet zone of the catalytic functional system for reducing tailpipe ammonia emissions, and the ammonia oxidation catalyst preferably comprising a three-way conversion (TWC) catalyst carrier-coated at the outlet zone of the catalytic functional system for reducing tailpipe ammonia emissions.

[0023] In another preferred embodiment, a washcoat comprising an ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion catalyst (TWC), is prepared from a slurry comprising at least one platinum group metal on a support without a step of thermally fixing the platinum group metal on the support.

[0024] In a second aspect of the present invention, a method for preparing an exhaust gas treatment system is provided, comprising the following steps:

[0025] - Provides a three-way conversion catalyst (TWC) and a gasoline particulate filter (GPF),

[0026] - preparing a first slurry comprising an ammonia oxidation catalyst (AMOx) by impregnating at least one catalytically active metal on an alumina support,

[0027] - preparing a second slurry comprising a selective catalytic reduction catalyst (SCR) comprising a metal-promoted zeolite,

[0028] - blending the first slurry and the second slurry to obtain a combined slurry comprising the ammonia oxidation catalyst (AMOx) from the first slurry and the selective catalytic reduction catalyst (SCR) from the second slurry,

[0029] - impregnating a support with the combined slurry to obtain a catalytically functional system for reducing tailpipe ammonia emissions, the catalytically functional system comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support, and

[0030] - Positioning the catalytic function system for reducing tailpipe ammonia emissions, including an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR), in the three-way conversion catalyst

[0031] (TWC) and downstream of the gasoline particulate filter (GPF).

[0032] In a preferred embodiment, the second slurry comprising a selective catalytic reduction catalyst (SCR) is prepared by providing a slurry comprising a non-metal promoted or metal promoted zeolite, and performing metal exchange of the zeolite by ion exchange in the slurry to obtain a second slurry comprising a selective catalytic reduction catalyst (SCR) containing a metal promoted zeolite.

[0033] In a third aspect of the present invention, a method for treating an exhaust gas flow from a gasoline engine is provided, comprising the steps of providing an exhaust gas flow containing ammonia from a gasoline engine, and contacting the exhaust gas flow containing ammonia with an exhaust gas treatment system according to the present invention to reduce ammonia emissions in the exhaust gas flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Various configurations of catalysts for use in the exhaust system of a gasoline engine are shown.

[0035] Figure 1 The first configuration shown in is a comparative reference system and includes a combination of a conventional TWC function system in this context and a gasoline particulate filter (GPF) located upstream, and then downstream another TWC catalyst in an underfloor position, which is largely insufficient to remove large amounts of ammonia. Figure 1 The last three configurations are according to the present invention and also include a conventional TWC functional system in combination with a gasoline particulate filter (GPF) upstream, followed by three different SCR / AMOx functional systems according to the present invention downstream of the TWC / GPF functional system. The catalysts in the four configurations were oven-aged at an internal oven temperature of 820°C for 15 hours under the specified gas composition.

[0036] Figure 1 The second and third configurations (the first and second inventive configurations, i.e., inventive Examples 1 and 2, respectively) may have several differences: In the second configuration (the first inventive configuration), the platinum group metal and the zeolite are used in one slurry to obtain a single slurry, single layer design for the SCR / AMOx functional system. In the third configuration, i.e., the second inventive configuration, the platinum group metal and the zeolite may be applied in the form of one slurry on the same ceramic honeycomb flow-through substrate under the same preparation conditions to obtain a single slurry, single layer design on the substrate, although preferably with slightly different total washcoat amounts. Furthermore, the third configuration (the second inventive configuration) may be derived from a different zeolite slurry process obtained from a so-called "in-slurry ion exchange" method, in which the Cu exchange is performed during the slurry process, compared to the second configuration (the first inventive configuration). Figure 1 Another difference in the third configuration (second inventive configuration) may be that the platinum group metal rhodium (Rh) is replaced by titanium (Ti) and manganese (Mn).

[0037] Figure 1 The fourth configuration (the third inventive configuration, such as Example 3 of the present invention) is different from all other configurations in that the conventional TWC / GPF functional system located upstream is followed by the SCR / AMOx functional system for removing ammonia, which is arranged in a partitioned configuration, resulting in the SCR and TWC / AMOx catalytic functional systems being presented at separate positions on the ceramic honeycomb flow-through substrate downstream of the TWC / GPF functional system.

[0038] Figure 2 It is shown in Figure 1 Plot of the observed carbon monoxide (CO) tailpipe emissions versus time for the four configurations described. Figure 2The figure also shows the speed applied in a Euro 6 GTDI vehicle with a chassis dynamometer test cell to further compare the four catalytic configurations.

[0039] Figure 3 It is shown in Figure 1 Plot of the observed tailpipe emissions of nitrogen oxides (NOx) over time for the four configurations described. Figure 3 The figure also shows the speed applied in a Euro 6 GTDI vehicle with a chassis dynamometer test cell to further compare the four catalytic configurations.

[0040] Figure 4 It is shown in Figure 1 Figure 2 shows the observed tailpipe emissions of ammonia (NH3) over time for the four configurations described. Figure 4 The figure also shows the speed applied in a Euro 6 GTDI vehicle with a chassis dynamometer test cell to further compare the four catalytic configurations.

[0041] Hereinafter, the exhaust gas treatment system of the present invention will be described in more detail.

[0042] As used herein, the terms "catalyst," "catalytically functional system," "catalyst component," "catalyst material," and the like refer to a material that promotes a reaction or reactions. Thus, the present invention is generally characterized by combining several catalytically functional systems in a single exhaust gas treatment line to synergistically remove several pollutants simultaneously from the tailpipe.

[0043] The individual catalytic functional systems of the exhaust gas treatment system for reducing ammonia emissions from a gasoline engine according to the present invention are defined in more detail below:

[0044] The exhaust gas treatment system according to the present invention includes a three-way conversion catalyst (TWC) downstream of the gasoline engine. The three-way conversion catalyst (TWC) is preferably located in close proximity to the gasoline engine, typically in a close-coupled position. More preferably, no other catalytic functional system is located between the gasoline engine outlet and the three-way conversion catalyst (TWC), and the three-way conversion catalyst (TWC) is the first catalytic functional system of the exhaust gas treatment system of the present invention located after the gasoline engine outlet.

[0045] As used herein, the terms "upstream" and "downstream" have their ordinary meaning in the art and are therefore also used herein to generally refer to the relative position of a catalytic functional system or component as compared to the relative position of another catalytic functional system or component in the exhaust system (or gasoline engine) based on the flow direction of the exhaust gas flow.

[0046] The term "close-coupled" refers to a location that is in fluid communication with and not far downstream of an engine outlet (preferably a gasoline engine outlet), preferably within 50 cm, more preferably within 30 cm, and most preferably within 20 cm after the engine outlet. Thus, in the context of the present invention, a "close-coupled" location is understood to be, as is commonly understood in the art, substantially closer to the engine than, for example, a conventional "underfloor" location (which is below the floor of the vehicle). Typically, but not exclusively, such a "close-coupled" location is preferably within the engine compartment, which is typically under the hood of the vehicle and adjacent to the exhaust manifold.

[0047] Therefore, a three-way conversion catalyst (TWC) positioned in a "close coupled" position is typically exposed to high temperature exhaust gases leaving the engine immediately after the engine is warmed up, and is therefore typically used to reduce hydrocarbon emissions during cold start, which is generally the period immediately after the engine is started from ambient conditions.

[0048] Hereinafter, the three-way conversion catalyst of the present invention will be described in more detail.

[0049] In the most general embodiment, the three-way conversion catalyst (TWC) is not particularly limited, but it is necessary to provide a common basic component of a three-way conversion catalyst (TWC) suitable for removing the three major pollutants produced by gasoline engines, which include unburned hydrocarbons (HC), nitrogen oxides (NOx) and carbon monoxide (CO).

[0050] Therefore, the composition of the three-way conversion catalytic washcoat is selected to contain hydrocarbon (HC) oxidizing components, carbon monoxide (CO) oxidizing components, and nitrogen oxide (NOx) reducing components, thereby allowing the removal of NOx, HC, and CO from the exhaust gas stream of the gasoline stream.

[0051] The three-way conversion catalyst (TWC) of the present invention comprises a platinum group metal (PGM) component, i.e., at least one platinum group metal. The platinum group metal (PGM) component is combined with a suitable support material (typically a refractory metal oxide support) in the catalyst. Considering long-term aging at high temperatures, the combination of the at least one platinum group metal (PGM) and the refractory metal oxide support can be important for achieving high catalyst performance and excellent stability.

[0052] The entire three-way conversion catalyst (TWC) is positioned on a suitable support material which allows positioning the three-way conversion catalyst (TWC) in the exhaust gas treatment line of the vehicle in an optimal manner. The support material is defined in more detail below.

[0053] Thus, a preferred three-way conversion catalyst (TWC) of the present invention for treating an exhaust gas stream containing nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) comprises at least one platinum group metal (PGM), a refractory metal oxide support and a carrier, characterized in that the platinum group metal (PGM) preferably comprises at least one platinum group metal selected from platinum, palladium and rhodium. A preferred combination of the at least one platinum group metal is palladium and rhodium, or alternatively, platinum and rhodium, or alternatively, a combination of the three platinum group metals platinum, palladium and rhodium, or alternatively, even only platinum and palladium.

[0054] In addition, additional platinum group metals (PGMs) other than platinum, palladium and rhodium may also be optionally present. For example, additional platinum group metals (PGMs) such as ruthenium, osmium and / or iridium may optionally be present in the three-way conversion catalyst (TWC) of the present invention.

[0055] If the at least one platinum group metal in the three-way conversion catalyst comprises platinum and palladium, the weight ratio of platinum to palladium in the three-way conversion catalyst (TWC) is preferably from 5:95 to 45:55, based on the total weight of the platinum group metals (PGM), and the refractory metal oxide support is preferably selected from a mixture or mixed oxide of ceria and alumina or lanthanum oxide-doped alumina, which contains up to 10 wt.% of lanthanum oxide, based on the weight of the lanthanum oxide-doped alumina, wherein more preferably, such three-way conversion catalyst (TWC) is in a position closely coupled to the engine outlet.

[0056] Even more preferably, the three-way conversion catalyst (TWC) is positioned in fluid communication with and shortly downstream of the engine outlet (preferably a gasoline engine outlet). Most preferably, the three-way conversion catalyst (TWC) of the present invention is located within 50 cm, more preferably within 30 cm, and most preferably within 20 cm after the engine outlet. It is also particularly preferred that the three-way conversion catalyst (TWC) is not located in an underfloor position, i.e., not under the vehicle floor.

[0057] In other words, the three-way conversion catalyst (TWC) is in a close-coupled position within the engine compartment, preferably under the hood of the vehicle and adjacent to the exhaust manifold. Thus, the three-way conversion catalyst (TWC) positioned in a "close-coupled" position is typically exposed to the high temperature exhaust gases leaving the engine immediately after the engine is warmed up, and is therefore typically used to reduce hydrocarbon emissions during cold starts, which is typically the period immediately after the engine is started from ambient conditions.

[0058] The total loading amount of the platinum group metal (PGM) component supported on the refractory metal oxide support in the three-way conversion catalyst (TWC) of the present invention may preferably be 1 g / ft 3 Up to 200g / ft 3 In the range of 20g / ft3 Up to 180g / ft 3 in the range of 50 g / ft 3 Up to 150g / ft 3 and most preferably 70 g / ft 3 Up to 125g / ft 3 Generally, a skilled person would be adept at determining the platinum group metal (PGM) loading on a catalytic coating. For example, XRF (X-ray fluorescence) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) can be used to measure the catalytic loading of the platinum group metal (PGM).

[0059] The three-way conversion 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-zeolite.

[0060] A preferred refractory metal support material comprises a mixture or mixed oxide of ceria and alumina. Preferably, the weight ratio of ceria to alumina in the mixture or mixed oxide of ceria and alumina is from 10:90 to 90:10, or from 25:75 to 75:25, or from 30:70 to 70:30, more preferably from 40:60 to 60:40, and even more preferably from 45:55 to 55:45.

[0061] Another preferred refractory metal support material is alumina, in particular high porosity alumina. Particularly preferred may be alumina doped with lanthanum oxide (e.g., La2O3). Lanthanum oxide-doped alumina refers to alumina containing a relatively small amount of lanthanum oxide, preferably up to 10% by weight, more preferably up to 7% by weight, even more preferably up to 5% by weight, and most preferably up to 4% by weight of lanthanum oxide, based on the weight of the lanthanum oxide-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 lanthanum oxide, based on the weight of the lanthanum oxide-doped alumina.

[0062] The alumina used in the refractory metal oxide support material of the present invention may preferably be stabilized alumina. The alumina of the refractory metal oxide support may also preferably be gamma alumina. The refractory metal oxide support of the three-way conversion catalyst (TWC) of the present invention may optionally contain additional metal oxides such as zirconium oxide, ceria, barium oxide, and / or neodymium oxide.

[0063] The total loading of the refractory metal oxide support in the three-way conversion catalyst (TWC) of the present invention is preferably 0.2 g / in 3 Up to 6.0g / in3 In the range of 0.5 g / in 3 Up to 5.0g / in 3 In the range of 1.0 g / in 3 Up to 4.0g / in 3 and even more preferably within the range of 2.5 g / in 3 Up to 3.5g / in 3 within the range.

[0064] The cerium oxide content in the three-way conversion catalyst (TWC) of the present invention is preferably 0.4 g / in 3 Up to 4.0g / in 3 In the range of 0.7 g / in 3 Up to 3.0g / in 3 in the range of 0.9 g / in 3 Up to 2.0g / in 3 In the range of 1.0 g / in 3 Up to 1.5g / in 3 within the range.

[0065] More preferably, the porosity of the refractory metal oxide support is in the range of 0.05 ml / g to 1.5 ml / g, more preferably in the range of 0.1 ml / g to 1.0 ml / g, more preferably in the range of 0.15 ml / g to 0.8 ml / g. The porosity of the refractory metal oxide support is determined by physical adsorption of N2 and analysis of the physical adsorption isotherm via BJH (Barett, Joyner, Halenda) analysis according to DIN 66134.

[0066] The three-way conversion catalyst (TWC) preferably comprises an additional oxygen storage component (OSC) and / or promoter component. The skilled person will understand the technical role that the additional oxygen storage component (OSC) and / or promoter component generally plays in a three-way conversion catalyst.

[0067] The three-way conversion catalyst (TWC) of the present invention preferably contains additional oxygen storage compounds. When several washcoats are applied to the three-way conversion catalyst (TWC) of the present invention, such oxygen storage compounds may be present in the bottom washcoat or the top washcoat, or in both the bottom washcoat and the top washcoat.

[0068] More preferably, the oxygen storage compound comprises cerium, and even more preferably comprises one or more of cerium oxide, an oxide mixture comprising cerium oxide, and a mixed oxide comprising cerium, wherein the mixed oxide comprising cerium preferably further comprises one or more of zirconium, yttrium, neodymium, lanthanum, and praseodymium, more preferably further comprises one or more of zirconium, yttrium, neodymium, and lanthanum, and more preferably further comprises zirconium, yttrium, neodymium, and lanthanum. Furthermore, the oxygen storage compound comprising cerium may be composed of two or more different mixed oxides, wherein each of these mixed oxides 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 a particularly preferred oxygen storage component.

[0069] The porosity of the oxygen storage compound is preferably in the range of 0.05 ml / g to 1.5 ml / g, more preferably in the range of 0.1 ml / g to 1.0 ml / g, and more preferably in the range of 0.15 ml / g to 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 DIN 66134.

[0070] The three-way conversion catalyst (TWC) preferably comprises an additional promoter component.As used in the context of the present invention, the term "promoter" relates to a compound which enhances the overall catalytic activity of the three-way conversion catalyst and / or contributes to its stability.

[0071] If the three-way conversion catalyst (TWC) of the present invention is a layered catalyst comprising several coatings (i.e., several washcoats, for example, including a bottom washcoat and a top washcoat), the promoter component may preferably be contained in 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, such as, for example, barium or zirconium oxide. A preferred promoter component is defined as a mixture of barium, zirconium, and neodymium, or a mixed oxide of barium, zirconium, and neodymium. If a ternary mixture of barium oxide, zirconium oxide, and neodymium oxide is used as the promoter component, the weight ratio of barium oxide, zirconium oxide, and neodymium oxide is preferably from 2:1:1 to 7:1:1, more preferably from 3:1:1 to 6:1:1, even more preferably from 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, more preferably is, one or more of a mixture of barium oxide and strontium oxide and a mixed oxide of barium and strontium. Another very preferred promoter is a mixture of barium oxide and zirconium oxide, or alternatively, barium oxide or zirconium oxide. If a mixture of barium oxide and zirconium oxide is used as the promoter component, the weight ratio of barium oxide to zirconium oxide is preferably from 0.5 to 5, more preferably from 1 to 3, even more preferably from 1.2 to 2.5. The preferred amount of the promoter component in the three-way conversion catalyst (TWC) of the present invention or in one of the washcoats (such as the bottom washcoat or the top washcoat) is defined as 0.01 g / in 3 Up to 0.5g / in 3 , more preferably 0.02 g / in 3 Up to 0.25g / in 3 in the range of or even more preferably 0.05 g / in 3 to 0.12g / in 3 Load within the range.

[0072] In the present invention, it is preferred that the three-way conversion catalyst has a layered design. That is, the three-way conversion catalyst of the present invention is preferably prepared by applying various catalytic functional systems or catalytic components to a carrier in the form of a coating or several coatings (usually referred to as one or more carrier coatings).

[0073] 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 compositionally distinct layer of material disposed on the surface of a monolithic substrate or optionally on an underlying washcoat layer. Washcoats typically consist of a refractory metal oxide support having a high surface area and 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.

[0074] Preferably, the three-way conversion catalyst (TWC) is preferably in the form of one or more washcoats, with a total loading on the support of 0.5 g / in 3 Up to 5g / in 3 In the range of 1.5 g / in 3 Up to 4.5g / in 3 In the range of 2.0 g / in 3 Up to 4.0g / in 3 and most preferably 2.7 g / in 3 Up to 3.5g / in 3 within the range.

[0075] The three-way conversion catalyst of the present invention can have a single washcoat layer comprising at least one platinum group metal (PGM) on a support material. For example, palladium can be impregnated on ceria-zirconia. In addition, rhodium can also be included in a single washcoat layer comprising palladium as a platinum group metal supported on ceria-zirconia, wherein the rhodium can be additionally supported on high-porosity alumina to form a preferred single washcoat layer comprising palladium supported on ceria-zirconia and rhodium supported on alumina. Promoter compounds such as zirconium oxide and / or barium oxide can optionally be added to the preferred single-layer design of the three-way conversion catalyst (TWC).

[0076] Alternatively, the three-way conversion catalyst (TWC) may comprise two or more washcoat layers, in particular two washcoat layers comprising a bottom washcoat and a top washcoat. Each washcoat layer may have a unique chemical catalytic functional system, depending on its exact composition. The bottom washcoat (or first washcoat) is applied to the substrate, and the top washcoat (or second washcoat) is applied over the bottom washcoat.

[0077] For the bottom washcoat or first washcoat (or first coating), a combination of palladium and / or 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 may optionally be present with palladium and / or platinum. In a preferred embodiment, the bottom washcoat may comprise palladium as the sole platinum group metal (PGM), with platinum and rhodium being absent. Alternatively, platinum and palladium are combined in the bottom washcoat in the absence of any other platinum group metals (PGMs).

[0078] Optionally, palladium may be combined with other platinum group metals (PGMs) such as ruthenium, osmium, and / or iridium in the bottom washcoat layer in the absence of platinum and rhodium.

[0079] 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 alumina and ceria. Another preferred refractory metal support material of the bottom washcoat comprises alumina doped with lanthanum. The alumina used for the refractory metal oxide support material may preferably be stabilized alumina. The alumina of the refractory metal oxide support of the bottom washcoat may also preferably be gamma alumina. The refractory metal oxide support of the bottom washcoat may optionally comprise additional metal oxides such as zirconium oxide, ceria, barium oxide, and / or neodymium oxide.

[0080] Another preferred refractory metal support material for the bottom washcoat layer comprises a mixture or mixed oxide of ceria and alumina. Preferably, the weight ratio of ceria to alumina in the mixture or mixed oxide of ceria and alumina is from 10:90 to 90:10, from 25:75 to 75:25, or from 30:70 to 70:30, more preferably from 40:60 to 60:40, and even more preferably from 45:55 to 55:45.

[0081] Another preferred refractory metal support material for the bottom washcoat layer comprises alumina doped with lanthanum oxide (e.g., La2O3). Lanthanum oxide doped alumina refers to alumina containing a relatively small amount of lanthanum oxide, preferably up to 10 wt%, more preferably up to 7 wt%, even more preferably up to 5 wt%, and most preferably up to 4 wt% of lanthanum oxide, based on the total weight of the lanthanum oxide doped alumina. La-doped alumina (L-doped alumina) contains at least 0.5 wt%, more preferably at least 1 wt%, and most preferably at least 2 wt% of lanthanum oxide, based on the total weight of the lanthanum oxide doped alumina.

[0082] For the top washcoat or second washcoat (or second coating), a combination of rhodium and palladium is preferably added as a platinum group metal (PGM), preferably in the absence of platinum. Other platinum group metals such as ruthenium, osmium and / or iridium may optionally be present together with rhodium and palladium. In a preferred embodiment, the top washcoat may even comprise rhodium as the sole platinum group metal (PGM), with platinum and palladium being absent. In another preferred embodiment, the top washcoat comprises rhodium, palladium and platinum. Optionally, in the absence of platinum and palladium, rhodium may be combined in the top coat with other platinum group metals (PGMs), such as ruthenium, osmium and / or iridium.

[0083] 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 alumina and ceria. Another preferred refractory metal support material of the top washcoat comprises alumina doped with lanthanum. The alumina used for the refractory metal oxide support material may preferably be stabilized alumina. The alumina of the refractory metal oxide support of the top washcoat may also preferably be gamma alumina. The refractory metal oxide support of the top washcoat of the present invention may optionally comprise additional metal oxides, such as zirconium oxide, ceria, barium oxide and / or neodymium oxide.

[0084] A preferred refractory metal support material for the top washcoat layer comprises a mixture or mixed oxide of ceria and alumina. Preferably, the weight ratio of ceria to alumina in the mixture or mixed oxide of ceria and alumina is from 10:90 to 90:10, from 30:70 to 70:30, more preferably from 40:60 to 60:40, and even more preferably from 45:55 to 55:45.

[0085] Another preferred refractory metal support material for the top washcoat layer comprises alumina doped with lanthanum, such as lanthanum oxide (e.g., La2O3). Lanthanum oxide-doped alumina refers to alumina containing a relatively small amount of lanthanum oxide, preferably at most 10 wt%, more preferably at most 7 wt%, even more preferably at most 5 wt%, and most preferably at most 4 wt% lanthanum oxide, based on the weight of the lanthanum oxide-doped alumina. La-doped alumina contains at least 0.5 wt%, more preferably at least 1 wt%, and most preferably at least 2 wt% lanthanum oxide, based on the weight of the lanthanum oxide-doped alumina.

[0086] The universal exhaust treatment system according to the present invention comprises a three-way conversion catalyst (TWC) and a gasoline particulate filter functional system. In a preferred embodiment, the exhaust treatment system of the present invention comprises a first three-way conversion catalyst (TWC) followed by a gasoline particulate filter (GPF) coated with a second three-way conversion catalyst (TWC). For example, the first three-way conversion catalyst (TWC) is positioned closely coupled to the engine, followed downstream by a gasoline particulate filter (GPF) coated with a second three-way conversion catalyst (TWC), preferably in a position closely coupled to the first three-way conversion catalyst (TWC).

[0087] The gasoline particulate filter (GPF) of the exhaust gas treatment system of the present invention can be a coated filter or a bare (exposed) filter. When the gasoline particulate filter (GPF) is not a coated filter, that is, a bare filter or exposed filter, there is no catalytically active coating on the filter medium. That is, particles from the exhaust gas flow are retained in a size-dependent manner in the pores of the filter medium and removed, while no chemical catalytic conversion occurs in the filter medium of the bare filter based on interaction with the catalytically active coating. The term "coated filter" (CF) generally refers to a device capable of removing particulate matter, which is generated by a gasoline engine and is carried into the exhaust gas flow to be removed by the exhaust gas treatment system of the present invention. The coated filter (CF) has as its basic feature a filter that is suitable for capturing particles from the exhaust gas flow based on the presence of a porous medium through which the exhaust gas flow can flow while the particulate matter is retained in the pores. In order to limit the back pressure of the exhaust gas flow, a coated filter is preferably used. That is, the porous medium having the filter function system can be coated with a catalytically active material, which catalytically active material optionally contributes to the conversion of pollutants in the exhaust gas flow flowing through the filter medium. The particles captured at the filter pores are burned into carbon dioxide at high temperatures and / or with the additional assistance of a catalytic coating. In this regard, it is preferred that the catalytically active coating on the coated filter (CF) helps prevent pore clogging and backpressure accumulation, which are typically caused by particle accumulation at the pores of the coated filter. The preferred catalytic coating on the coated filter of the gasoline particulate filter (GPF) is a three-way conversion catalyst (TWC), as described elsewhere herein. Therefore, the coated filter (CF) preferably provides a second three-way conversion catalyst (TWC) function for the exhaust gas treatment system of the present invention. A possible coated filter (CF) is a four-way conversion catalyst (FWC), which is more preferably located adjacent to the three-way conversion catalyst (TWC), for example, in a position closely coupled to the first three-way conversion catalyst (TWC). As will be understood by those skilled in the art, a coated filter (CF) comprising a second three-way conversion catalyst (TWC) (such as a four-way conversion catalyst (FWC)) integrates the typical three-way conversion catalyst (TWC) function and the additional particle removal function. Therefore, the exhaust gas treatment system of the present invention can preferably combine two three-way conversion catalyst (TWC) functional systems, wherein, more preferably, the second TWC located downstream, for example due to the presence of a filter, preferably a gasoline particulate filter (GPF), also includes a catalytic functional system for removing particulate matter.

[0088] When the particle filter is a coated particle filter, the particle filter serves as a substrate on which a second three-way conversion catalyst (TWC) can be applied to the surface or pores of the particle filter. As described in more detail above, the second three-way conversion catalyst (TWC) functional system of the coated filter (CF), preferably a four-way conversion catalyst (FWC), can be present in the form of a single washcoat or several washcoats (e.g., two different washcoats or coatings) for the three-way conversion catalyst (TWC).

[0089] The capture of particulate matter in a gasoline particulate filter (GPF) can be accomplished, for example, by using a particle (or soot) filter, by using a flow-through substrate with an internal tortuous path, such that the flow direction of the particles is changed so that they fall out of the exhaust gas stream. A typical monolithic substrate has thin, parallel gas flow channels extending therethrough from either the inlet or outlet face of the substrate, such that the channels are open to fluid flow therethrough (a "flow-through substrate").

[0090] The flow-through substrate can be a monolithic substrate, including a flow-through honeycomb monolithic substrate. Flow-through substrates are familiar to those skilled in the art and typically have thin, parallel gas flow channels extending from an inlet end to an outlet end of the substrate such that the channels are open to fluid flow. The channels, which are essentially straight paths from their fluid inlet to their fluid outlet, are defined by walls on which a catalytic coating can be disposed so that the gas flowing through the channels contacts the catalytic material. The flow channels of the flow-through substrate are thin-walled channels that can have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, and the like. As further described below, the flow-through substrate can be ceramic or metallic. For example, the flow-through substrate can have a cross-sectional shape of about 50 in. 3 to about 1200in 3 volume, a pore density (inlet opening) of about 60 pores per square inch (cpsi) to about 1200 cpsi or about 200 cpsi to about 900 cpsi or, for example, about 300 cpsi to about 600 cpsi, and a wall thickness of about 50 microns to about 400 microns or about 100 microns to about 200 microns.

[0091] Suitable substrates are preferably ceramic substrates made of any suitable refractory material, for example, cordierite, cordierite-α-alumina, aluminum titanate, silicon titanate, silicon carbide, silicon nitride, zircon mullite, spodumene, alumina-silica-magnesium, zirconium silicate, sillimanite, magnesium silicate, zircon, petalite, α-alumina, aluminosilicates, and the like.

[0092] The most preferred substrate in the present invention is a wall-flow filter substrate. As will be appreciated by those skilled in the art, a wall-flow filter substrate has a plurality of thin, substantially parallel gas flow channels extending along the longitudinal axis of the substrate, wherein typically each channel is blocked at one end of the substrate body, while alternate channels are blocked at the opposite end face ("wall-flow filter"). Suitable flow-through and wall-flow substrates are also taught, for example, in International Application Publication No. WO 2016 / 070090, which is incorporated herein by reference in its entirety.

[0093] Preferably, the wall flow filter substrate comprises, more preferably consists of, cordierite, silicon carbide, aluminum titanate, or a combination thereof.

[0094] Preferably, in a gasoline particulate filter (GPF) optionally comprising a second three-way conversion (TWC) function, more preferably a four-way conversion catalyst, the three-way conversion functional system is presented on the particle filter by penetrating the wall of the particle filter function. In this preferred embodiment, there is no layering of three-way conversion catalytic material on the surface of the wall of the particle filter function system of the gasoline particulate filter (GPF). More preferably, in this preferred arrangement, the resulting four-way conversion catalyst comprising the particle filter function system has a coated porosity less than that of a bare particle filter. More preferably, the coated porosity may be between 75% and 98% of the uncoated porosity, or the coated porosity may be between 80% and 95% of the uncoated porosity, or the coated porosity may be between 80% and less than 93% of the uncoated porosity.

[0095] The gasoline particulate filter (GPF) may preferably include a catalytically active coating that includes a three-way conversion catalyst (TWC) function. The three-way conversion catalyst (TWC) coating of the coated filter (CF), preferably a four-way conversion catalyst (FWC), may preferably be formed from a single washcoat composition that penetrates the inlet side, the outlet side, or both the inlet and outlet sides of the particulate filter.

[0096] Alternatively, several, preferably two, three-way conversion catalyst (TWC) coatings of a coated filter (CF), preferably a four-way conversion catalyst (FWC), may be formed from several, preferably two, washcoat compositions. Different washcoat compositions may be applied to penetrate the inlet and outlet sides. Alternatively, a single washcoat composition or several washcoat compositions may be applied to both the inlet and outlet sides of the particle filter.

[0097] The catalytically active coating of the three-way conversion catalyst (TWC) material on the coated filter (CF) may be approximately 1 g / in 3 to about 5g / in 3(about 60 g / L to about 300 g / L). The uncoated porosity may be in the range of 55% to 70%. More preferably, the coated filter (CF) contains 120 g / L to 244 g / L (about 1.0 g / in 3 to about 4.0g / in 3 ) and having a porosity in the range of 55% to 70%, wherein the particulate filter functional system has a wall thickness of about 152 μm (6 mils) to about 356 μm (14 mils). In this embodiment, the three-way conversion catalyst (TWC) penetrates the wall of the particulate filter without layering of catalytic material on the surface of the particulate filter wall. Preferably, no three-way conversion catalytic material is present outside the pores of the particulate filter wall.

[0098] Specific coated filters (CF), preferably four-way conversion catalysts and their preparation are described in WO 2019 / 149929A1, WO 2019 / 149930A1 and WO 2020 / 043885A1, which are incorporated herein by reference in their entirety.

[0099] As a coated particle filter, a coated filter (CF), preferably a four-way conversion catalyst (FWC), can be prepared by applying a three-way conversion catalyst (TWC) coating on a particle filter as follows:

[0100] A suitable particle filter substrate is provided, a slurry of a three-way conversion (TWC) catalytic material is formed at a pH in the range of 2 to 7; and the three-way conversion catalytic (TWC) material is infiltrated into the wall of the particle filter to form a coated filter (CF), preferably a four-way conversion catalyst (FWC), having a particle filter functional system, such that the coated porosity of the coated filter (CF) is less than the uncoated porosity of the particle filter. The dynamic viscosity of the slurry at 20°C may be in the range of about 5 mPas to less than 40 mPas, and the solids content is 0 wt% to 25 wt% solids. The pH may be in the range of 3 to 5. Preferably, there is no layering of catalytic material on the surface of the wall of the particle filter, except optionally in the area of overlapping washcoats. In a preferred embodiment, there is no catalytic material outside the pores of the wall of the particle filter. The coated porosity may be linearly proportional to the washcoat loading of the three-way conversion catalytic (TWC) material. The coated porosity may be between 75% and 98% of the uncoated porosity, or even between 80% and 95% of the uncoated porosity, or even between 80% and less than 93%. Preferably, the particulate filter may have 200 to 300 pores per square inch (OPSI) and a wall thickness in the range of 6 mils to 14 mils.

[0101] To further reduce ammonia emissions from gasoline engines, the exhaust gas treatment system of the present invention combines a three-way conversion catalyst (TWC) and a coated filter (CF), preferably a four-way conversion catalyst (FWC), with a suitable catalytic function system for reducing tailpipe ammonia emissions. The present invention achieves this objective through a combination comprising at least a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx).

[0102] There are two basic options for including a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx) in the exhaust gas treatment system of the present invention. In a first alternative, the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined in a single layer on a substrate. In a second alternative, the combination of the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) is a zoned catalytic functional system, in which the selective catalytic reduction catalyst (SCR) comprising a metal-promoted zeolite and the ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion (TWC) catalyst, are positioned in separate locations on a suitable support or carrier. Preferably, the selective catalytic reduction catalyst (SCR) comprising a metal-promoted zeolite is support-coated at the inlet zone of the catalytic functional system for reducing tailpipe ammonia emissions, and the ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion (TWC) catalyst, is support-coated at the outlet zone of the catalytic functional system for reducing tailpipe ammonia emissions.

[0103] The SCR catalyst used in the present invention may comprise, for example, one or more metal oxides (eg, mixed oxides), molecular sieves (preferably metal-promoted molecular sieves), or combinations thereof.

[0104] The SCR catalyst preferably comprises one or more molecular sieve materials. More preferably, the SCR catalyst material comprises an 8-membered ring small pore molecular sieve containing a metal promoter. As used herein, "small pore" refers to a pore size of less than about 5 angstroms (e.g., about to about to about to or about to For example, a pore opening of about 3.8 angstroms. A particularly preferred 8-membered ring small pore molecular sieve is an 8-membered ring small pore zeolite.

[0105] The SCR catalytic material preferably comprises a zeolite, preferably a zeolite comprising d6r units. Thus, the SCR catalytic material may comprise a zeolite having a structure type selected from the group consisting of AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, WEN, and combinations thereof. Preferred SCR catalytic materials comprise a zeolite having a structure type selected from the group consisting of CHA, AEI, AFX, ERI, KFL, LEV, and combinations thereof. Particularly preferred SCR catalytic materials comprise a zeolite having a structure type selected from the group consisting of CHA and AEI. The most preferred SCR catalytic material comprises a zeolite having a CHA structure type.

[0106] The SCR catalytic material containing chabazite is preferably a zeolite having a composition of (Ca, Na2, K2, Mg)Al2Si4O 12 ·A naturally occurring framework silicate mineral of the zeolite class (e.g., hydrated calcium aluminum silicate) having an approximate formula represented by 6H2O. Three synthetic forms of chabazite that may be advantageously used in the SCR catalyst of the present invention are described in "Zeolite Molecular Sieves" by DW Breck, published by John Wiley & Sons in 1973, which is incorporated herein by reference. The three synthetic forms reported by Breck are Zeolite KG, described in J. Chem. Soc., p. 2822 (1956), Barrer et al.; Zeolite D, described in British Patent No. 868,846 (1961); and Zeolite R, described in U.S. Patent No. 3,030 to Milton, all of which are incorporated herein by reference. The synthesis of another synthetic form of chabazite, SSZ-13, is described in U.S. Patent No. 4,544,538 to Zornes, which is incorporated herein by reference. A method for preparing yet another synthetic molecular sieve, SAPO-44, having a chabazite structure, is described in US Patent No. 6,162,415 to Liu et al., which is incorporated herein by reference.

[0107] The ratio of silica to alumina in the molecular sieve used as the SCR catalytic material in the present invention can vary over a wide range. Preferred molecular sieves that can be used as SCR catalytic materials have a silica to alumina molar ratio (SAR) of 2 to 300, including 5 to 250, 5 to 200, 5 to 100, and 5 to 50. More preferably, the molecular sieve has a silica to alumina molar ratio (SAR) of 10 to 200, 10 to 100, 10 to 75, 10 to 60, 10 to 50, 15 to 100, 15 to 75, 15 to 60, 15 to 50, 20 to 100, 20 to 75, 20 to 60, and 20 to 50. Even more preferably, for molecular sieves having any of the above SAR ranges, the spherical particles of the molecular sieve have a particle size d in the range of about 1.0 micron to about 5 microns and more specifically about 1.0 micron to about 3.5 microns. 50 , and the individual crystals of the molecular sieve component have a crystal size in the range of about 100 nm to about 250 nm.

[0108] Preferred metal-promoted zeolite catalysts, including iron-promoted and copper-promoted zeolite catalysts, are used for the selective catalytic reduction of nitrogen oxides with, for example, ammonia. The promoter metal may be selected from Cu, Fe, Co, Ni, La, Ce, Mn, V, Ag, and combinations thereof. Preferred promoter metals are Cu, Fe, or combinations thereof. Therefore, preferred metal-promoted zeolites included in the selective catalytic reduction (SCR) catalyst of the present invention are copper-promoted zeolites or iron-promoted zeolites, particularly copper-promoted chabazite or iron-promoted chabazite, or both.

[0109] Preferred SCR catalysts do not contain any precious metals or platinum group metals, such as rhodium, palladium, and / or platinum. Metal-promoted, particularly copper-promoted, aluminosilicate zeolites having a CHA structure type and a silica to alumina molar ratio greater than 1 have recently attracted significant attention as catalysts for the selective catalytic reduction of nitrogen oxides using nitrogen-containing reductants in lean-burn engines. In such preferred catalysts, the promoter metal content, calculated as oxide, is preferably at least about 0.1 wt %, reported on a volatile-free basis. Preferably, the promoter metal comprises Cu, and the Cu content, calculated as CuO, is in the range of up to about 10 wt %, or more preferably 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt %, 0.5 wt %, and 0.1 wt %, in each case based on the total weight of the calcined zeolite component, reported on a volatile-free basis. The Cu content, calculated as CuO, may range from about 1 wt % to about 4 wt %.

[0110] An exemplary molecular sieve that can be used as an SCR catalytic material is an aluminophosphate. Types of aluminophosphates include silicoaluminophosphates (SAPOs), metalloaluminophosphates (MeAPOs), and metalloaluminophosphates (MeSAPOs). The preparation of a synthetic form of an exemplary aluminophosphate molecular sieve, silicoaluminophosphate 34 (SAPO-34), is described in U.S. Patent Nos. 4,440,871 to Van et al. and 7,264,789 to VanDen et al., which are incorporated herein by reference. A method for preparing yet another synthetic molecular sieve, SAPO-44, is described in U.S. Patent No. 6,162,415 to Liu et al., which is incorporated herein by reference.

[0111] The SCR catalyst of the present invention preferably comprises a metal oxide, such as a mixed oxide. As used herein, the term "mixed oxide" refers to an oxide containing cations of more than one chemical element or cations of a single element in several oxidation states. Mixed oxides suitable as SCR catalysts may include Fe / titania (e.g., FeTiO3), Fe / alumina (e.g., FeAl2O3), Mg / titania (e.g., MgTiO3), Mg / alumina (e.g., MgAl2O3), Mn / alumina, Mn / titania (e.g., MnO x / TiO2)(e.g. MnO x

[0014] Examples of mixed oxides used as SCR catalysts include Cu / Al2O3), Cu / titanium dioxide (e.g., Cu1TiO3), Ce / Zr (e.g., CeZrO2), Ti / Zr (e.g., TiZrO2), and mixtures thereof. Additional examples of mixed oxides used as SCR catalysts can be found in U.S. Patent Application Publication No. 2001 / 0049339 to Schafer-Sindelindger et al. and U.S. Patent Nos. 4,518,710 to Brennan et al., 5,137,855 to Hegedus et al., 5,476,828 to Kapteijn et al., 8,685,882 to Hong et al., and 9,101,908 to Jurng et al., all of which are incorporated herein by reference in their entirety.

[0112] The SCR catalyst may include one or more vanadium-containing components. Such compositions are generally referred to as "vanadium oxide-based compositions" in this article. In such embodiments, vanadium can be in various forms, for example, including but not limited to free vanadium, vanadium ions or vanadium oxides (vanadium oxide / vanadia), such as vanadium pentoxide (V2O5). As used herein, "vanadium oxide (vanadia / vanadium oxide)" is intended to encompass any oxide of vanadium, including vanadium pentoxide. Compositions based on vanadium oxide preferably include mixed oxides comprising vanadium oxide. The amount of vanadium oxide in the mixed oxide can vary, and preferably, based on the total weight of the mixed oxide, in the range of about 1 wt% to about 10 wt%. For example, the amount of vanadium oxide can be at least 1 wt%, at least 2 wt%, at least 3 wt%, at least 4 wt%, at least 5 wt% or at least 6 wt%, with an upper limit of about 10 wt% or not more than 10 wt%, not more than 9 wt%, not more than 8 wt%, not more than 7 wt%, not more than 6 wt%, not more than 5 wt% or not more than 4 wt%, and a lower limit of about 1 wt%.

[0113] Preferred SCR compositions include vanadium supported on refractory pure oxides such as alumina, silica, zirconia, titania, ceria, and combinations thereof, as described in U.S. Patent Nos. 4,010,238 to Shiraishi et al. and 4,085,193 to Nakajima et al., and U.S. Patent Application Publication No. 2017 / 0341026 to Chen et al., all of which are incorporated herein by reference in their entirety. In other preferred embodiments, the SCR catalyst comprises a mixed oxide comprising vanadium oxide / titanium dioxide (VO / TiO), for example, in the form of titania with vanadium oxide dispersed thereon. The vanadium oxide / titania may optionally be activated or stabilized with tungsten (e.g., WO) to provide VO / TiO / WO, for example, in the form of titania with VO and WO dispersed thereon. The vanadium oxide is not always present as a true mixed metal oxide; instead, the metal oxide components (e.g., titania and vanadium oxide) may be present as discrete particles. In such embodiments, the amount of tungsten can vary and can be, for example, in the range of about 0.5 wt % to about 10 wt %, based on the total weight of the mixed oxide. For example, the amount of tungsten can be at least 0.5 wt %, at least 1 wt %, at least 2 wt %, at least 3 wt %, at least 4 wt %, at least 5 wt %, or at least 6 wt %, with an upper limit of about 10 wt %, or no more than 10 wt %, no more than 9 wt %, no more than 8 wt %, no more than 7 wt %, no more than 6 wt %, no more than 5 wt %, or no more than 4 wt %, and a lower limit of about 0.5 wt %.

[0114] Exemplary vanadium oxide-based SCR compositions may include, but are not limited to, V2O5 / TiO2, V2O5 / WO3 / TiO2 / SiO2, or combinations thereof. Additional vanadium-containing SCR catalyst compositions are described, for example, in U.S. Patent Nos. 4,782,039 to Lindsey and 8,975,206 to Schermanz et al., and International Application Publication No. WO 2010 / 121280 to Schermanz et al., all of which are incorporated herein by reference in their entirety.

[0115] Certain vanadium oxide-based SCR compositions may include other active components (e.g., other metal oxides). For example, in some embodiments, vanadium oxide-based SCR compositions suitable for use in the disclosed systems include vanadium oxide and antimony. In certain embodiments, such vanadium oxide-based SCR compositions include a composite oxide containing vanadium and antimony that may be supported on a refractory metal oxide (e.g., TiO2, SiO2, WO3, Al2O3, ZrO2, or a combination thereof). Exemplary vanadium oxide-based SCR compositions comprising vanadium oxide and antimony are disclosed in U.S. Patent No. 4,221,768 to Inoue et al., International Application Publication No. WO 2017 / 101449 to Zhao et al., and International Application Nos. PCT / CN2016 / 113637, filed on December 30, 2016; PCT / CN2015 / 076895, filed on April 17, 2015, and PCT / CN2015 / 097704, filed on December 17, 2015, all of which are incorporated herein by reference in their entireties. In certain embodiments, the SCR catalyst may comprise a mixture of the vanadium-based SCR composition and a molecular sieve.

[0116] As used herein, the term "ammonia oxidation catalyst" (AMOx) refers to a catalyst containing one or more catalytic metals on a substrate or support, preferably an alumina support, which is suitable for converting excess ammonia in the exhaust system to nitrogen.

[0117] Ammonia oxidation (AMOx) generally refers to a process in which ammonia preferentially reacts with oxygen to produce N2. Ammonia oxidation catalysts (AMOx) are able to convert excess ammonia primarily into N2, preferably over a wide temperature range, with minimal nitrogen oxide byproducts, such as NOx, which might otherwise escape during the vehicle's driving cycle. Consequently, AMOx catalysts also minimize the production of N2O, an undesirable and potent greenhouse gas.

[0118] The composition of the AMOx catalyst is not particularly limited, and in the context of the disclosed exhaust gas treatment system, various compositions known to be suitable for this purpose may be used. Preferably, the ammonia oxidation catalytic component is generally a composition comprising one or more platinum group metals supported on a refractory metal oxide, preferably a physical mixture.

[0119] The AMOx catalyst may preferably include at least one supported platinum group metal that effectively removes ammonia from the exhaust gas stream. Preferred platinum group metals include ruthenium, rhodium, iridium, palladium, platinum, silver, or gold. The platinum group metal component may include physical mixtures and / or chemically and / or atomically doped combinations of ruthenium, rhodium, iridium, palladium, platinum, silver, and gold. In highly preferred embodiments, the AMOx catalyst comprises a precious metal or platinum group metal (PGM), such as platinum, palladium, rhodium, or a combination thereof. It is particularly preferred that the AMOx catalyst comprises platinum. It is highly preferred that the at least one platinum group metal, most preferably platinum, and optionally platinum and rhodium, be present in an amount of from about 0.008 wt % to about 2 wt % (metal), based on the Pt group metal support loading.

[0120] The AMOx catalytic functional system according to the present invention comprises about 0.1 g / ft 3 to about 10g / ft 3 , preferably about 0.3 g / ft 3 to about 5g / ft 3 , more preferably about 0.5 g / ft 3 About 3g / ft 3 , even more preferably about 0.8 g / ft 3 About 2g / ft 3 % to about 1 wt %, more preferably about 0.08 to about 0.5 wt %, based on the weight of the dry AMOx catalyst component.

[0121] Preferably, the precious metal component or platinum group metal of the ammonia oxidation catalytic component comprises platinum (Pt), preferably consists of it. The ammonia oxidation catalyst comprises or consists of a platinum (Pt) component in an amount of about 0.5 g / ft 3 to about 10g / ft 3 %, more preferably in the range of about 0.01 wt. % to about 2 wt. %, or alternatively, the total platinum loading and / or the amount of platinum is as defined above for common noble metals or platinum group metals.

[0122] Alternatively, the precious metal component or platinum group metal of the ammonia oxidation catalytic component comprises palladium (Pd), preferably consists of palladium (Pd). The ammonia oxidation catalyst comprises or consists of a palladium (Pd) component in an amount of about 0.5 g / ft 3 to about 10g / ft 3 %, more preferably in the range of about 0.01 wt. % to about 2 wt. %, or alternatively, the total loading of palladium and / or the amount of palladium is as defined above for common noble metals or platinum group metals.

[0123] Alternatively, the noble metal component or platinum group metal of the ammonia oxidation catalytic component comprises rhodium (Rh), preferably consists of it. The ammonia oxidation catalyst comprises or consists of a rhodium (Rh) component in an amount of about 0.5 g / ft 3 to about 10g / ft 3 %, more preferably in the range of about 0.01 wt. % to about 2 wt. %, or alternatively, the total loading of rhodium and / or the amount of rhodium is as defined above for common noble metals or platinum group metals.

[0124] Those skilled in the art will be familiar with determining the loading of the noble metal or platinum group metal on the catalytic coating. For example, XRF (X-ray fluorescence) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) can be used to measure the catalytic loading.

[0125] The noble metal or platinum group metal of the AMOx catalyst of the present invention is preferably supported on, for example, a high surface area refractory metal oxide support. Examples of suitable high surface area refractory metal oxides include, but are not limited to, alumina, silica, titania, ceria, and zirconia, as well as physical mixtures, chemical combinations, and / or atomically doped combinations thereof. The refractory metal oxide may contain mixed oxides such as silica-alumina, amorphous or crystalline aluminosilicates, alumina-zirconia, alumina-lanthanum oxide, alumina-chromium oxide, alumina-barium oxide, alumina-ceria, and the like. Exemplary refractory metal oxides include high surface area gamma-alumina, preferably having a surface area of about 50 m 2 / g to about 300m 2 / g specific surface area.

[0126] Preferred refractory metal oxide supports useful in the AMOx compositions of the present invention are alumina or doped alumina materials, such as Si-doped alumina materials (including but not limited to 1% to 10% SiO2-Al2O3), titania or doped titania materials, such as Si-doped titania materials (including but not limited to 1% to 15% SiO2-TiO2), or zirconia or doped zirconia materials, such as Si-doped ZrO2 (including but not limited to 5% to 30% SiO2-ZrO2).

[0127] High surface area metal oxide supports, such as alumina or titania support materials, typically exhibit a surface area of about 50 m 2 / g to about 400m 2 / g and preferably about 60m 2 / g to about 350m 2 / g, for example, about 90m 2 / g to about 250m 2 / g total surface area (BET).

[0128] The refractory metal oxide support material preferably has a thickness of about 0.3 cm 3 / g to about 1.5cm 3 The total pore volume (BET) of the activated alumina is in the range of 2 nm to 50 nm.

[0129] In one or more embodiments, the ammonia oxidation catalyst (AMOx) has a particle size distribution D of about 1 micron to about 10 microns. 50 , and / or the ammonia oxidation catalyst has a particle size distribution of about 2 microns to about 30 microns 90 .

[0130] In one or more embodiments, the ammonia oxidation catalyst (AMOx) has a 2 / g to about 700m 2 In one or more embodiments, the ammonia oxidation catalyst has a surface area of about 0.3 cm 3 / g to about 1.5cm 3 In one or more embodiments, the ammonia oxidation catalyst has an average pore volume (BET) in the range of about 2 nm to about 50 nm. In one or more embodiments, the ammonia oxidation catalyst has an average pore volume (BET) in the range of about 0.3 g / in 3 to about 3.0g / in 3 The dry extender is applied to the substrate.

[0131] In a preferred embodiment, the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention includes an additional three-way conversion catalyst (TWC). Those skilled in the art will be familiar with the common features of three-way conversion catalysts (TWCs) as described in the art. In addition, the three-way conversion catalyst (TWC) has been described above with respect to a TWC to be positioned in a close-coupled position at the outlet of a gasoline engine. Therefore, these descriptions also apply to the three-way conversion catalyst (TWC) added to the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention.

[0132] The most important difference between the three-way conversion catalyst (TWC) preferably included in the ammonia oxidation catalyst (AMOx) and the ammonia oxidation catalyst (AMOx) itself is that the three-way conversion catalyst (TWC) includes an oxygen storage component (OSC). It is well known that the presence of an oxygen storage component (OSC) in the three-way conversion catalyst (TWC) is crucial for the synergistic removal of nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) from the exhaust gas stream of a gasoline engine. Therefore, the preferred three-way conversion catalyst (TWC) included in the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention includes an additional oxygen storage component (OSC). As described elsewhere herein, the preferred oxygen storage component (OSC) is a ceria-based material, i.e., a cerium oxide-based material, which can preferably be used as a support material for at least one platinum group metal of the three-way conversion catalyst (TWC) of the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention. As described in more detail herein, particularly preferred are materials comprising one or more cerium oxides or ceria with other oxides. Very preferred are mixed oxides (or even mixtures) of ceria and zirconia.

[0133] In some embodiments, the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention may be free of an additional oxygen storage component (OSC), and thus effectively free of a three-way conversion catalyst (TWC), particularly when the ammonia oxidation catalyst (AMOx) as defined herein is combined with an additional selective catalytic reduction catalyst (SCR) in a single catalytic layer. Alternatively, the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention may preferably comprise a catalytic functional system that, due to the presence of the oxygen storage component (OSC), constitutes a three-way conversion catalyst (TWC). This latter configuration is particularly preferred when the catalytic functional system for reducing tailpipe ammonia emissions comprises a combination of at least a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx), wherein the latter two catalytic functional systems are selected for zoned presentation. In this preferred configuration, the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are positioned separately from the optional three-way conversion catalyst (TWC), preferably at the inlet and outlet of the flow-through support material, respectively.

[0134] One advantage of a zoned configuration of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx), preferably including an additional three-way conversion catalyst (TWC), is that the amount of the selective catalytic reduction catalyst (SCR) and / or the ammonia oxidation catalyst (AMOx), preferably including a three-way conversion catalyst (TWC), can be significantly reduced compared to a configuration in which the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined in a single catalytic washcoat layer. Without being bound by a particular theory, the inventors believe that the zoned configuration of the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) presents the following technical advantages: the latter two catalytic functional systems are not in direct contact with each other, even when the corresponding exhaust gas treatment system is operated for a long time under challenging real-world conditions, including long-term aging of the entire system at high temperatures and in harsh environmental conditions. Thus, due to the permanent separation of the catalytic functional systems at different locations, the inventors believe that the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx), preferably with a three-way conversion catalyst (TWC), cannot directly interact with each other and / or adversely affect the mutual stability of the respective catalytic functional systems, thereby allowing the overall catalytic functional system to have better long-term stability and effectiveness in reducing ammonia emissions at the tailpipe. Clearly, the additional option of limiting or even significantly reducing the amount of catalysis in more efficient or at least comparable exhaust gas treatment systems that can meet future emission regulations could provide significant technical benefits.

[0135] When the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined in a single layer on a substrate, it is preferred that the single layer is prepared from a combined slurry comprising a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx), the selective catalytic reduction catalyst comprising a metal-promoted zeolite. However, the single combined slurry used to prepare a single layer comprising a catalytic functional system for reducing tail pipe ammonia emissions is preferably obtained by blending a first slurry and a second slurry prepared separately. The first slurry is used to prepare an ammonia oxidation catalyst (AMOx), which comprises at least one catalytically active metal on an alumina support. The second slurry is used to prepare a selective catalytic reduction catalyst (SCR), which comprises a metal-promoted zeolite. The first slurry and the second slurry are blended into a single combined slurry comprising at least a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx) to obtain a single slurry, single layer design of the present invention according to this first alternative of the catalytic functional system, which is used to reduce tail pipe ammonia emissions of the exhaust gas treatment system of the present invention.

[0136] Therefore, in a preferred alternative, a method for preparing an exhaust gas treatment system of the present invention comprises the following steps: providing a three-way conversion catalyst (TWC) and a gasoline particulate filter (GPF), preferably a four-way conversion catalyst (FWC); preparing a first slurry comprising an ammonia oxidation catalyst (AMOx) by impregnating at least one catalytically active metal on an alumina support; preparing a second slurry comprising a selective catalytic reduction catalyst (SCR), the selective catalytic reduction catalyst comprising a metal-promoted zeolite; blending the first slurry and the second slurry to obtain a slurry comprising the ammonia oxidation catalyst (AMOx) from the first slurry and the SCR catalyst (SCR). A single combined slurry of a selective catalytic reduction catalyst (SCR) from the second slurry; impregnating a carrier with the single combined slurry to obtain a catalytic functional system for reducing tailpipe ammonia emissions, the catalytic functional system comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on the carrier; and positioning the catalytic functional system for reducing tailpipe ammonia emissions comprising the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR) downstream of a three-way conversion catalyst (TWC) and a gasoline particulate filter (GPF), preferably a four-way conversion catalyst (FWC).

[0137] Preferably, at least one catalytically active metal on an alumina support (impregnated on alumina, preferably zirconium oxide-doped alumina), preferably platinum and / or rhodium, or alternatively palladium and / or rhodium, or even a combination of platinum and palladium with rhodium, is thermally fixed to obtain a first slurry. The solids content of the first slurry is preferably in the range of 50% to 85% by weight, more preferably 60% to 80% by weight, or even more preferably 70% to 75% by weight. Alternatively, the at least one catalytically active metal on the alumina support may be free of any rhodium and comprise a combination of platinum and / or palladium with at least one non-platinum group metal (such as titanium and / or manganese in place of rhodium), which is typically impregnated on an alumina support, in particular by thermal fixing. The solids content of the first slurry is preferably in the range of 50% to 85% by weight, more preferably 55% to 75% by weight, or even more preferably 60% to 70% by weight.

[0138] Preferably, the particle size distribution D of the first slurry containing the ammonia oxidation catalyst (AMOx) is 90 The ammonia oxidation catalyst comprises at least one catalytically active metal on an alumina support in the range of 1 to 38 microns, preferably 5 to 30 microns, more preferably 8 to 27 microns and most preferably 12 to 22 microns.

[0139] It is also preferred in this method that the particle size distribution D of the single combined slurry used in the catalytic functional system for reducing tail pipe ammonia emissions is obtained. 90The single combined slurry comprises an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support in the range of 2 microns to 50 microns, preferably 5 microns to 30 microns, more preferably 8 microns to 25 microns, and most preferably 10 microns to 17 microns.

[0140] In a preferred embodiment, the second slurry containing the selective catalytic reduction catalyst (SCR) may already contain a metal-promoted zeolite containing a catalytic functional system. That is, before forming the second slurry by providing the metal-promoted zeolite into the second slurry, the metal-promoted zeolite is formed separately, for example, by metal exchange or metal promotion of a metal-free zeolite. In this preferred embodiment, a metal-promoted zeolite, such as a copper- or iron-promoted zeolite, more preferably a copper- or iron-promoted chabazite, is added to the second slurry, and the second slurry is then blended with a first slurry containing an ammonia oxidation catalyst (AMOx), the ammonia oxidation catalyst containing at least one catalytically active metal on an alumina support. Preferably, the particle size distribution D of the second slurry containing the selective catalytic reduction catalyst (SCR) is 90 In the range of 0.5 micron to 25 micron, preferably 1 micron to 20 micron, more preferably 2 micron to 15 micron and most preferably 3 micron to 8 micron. Optionally, zirconium oxide can be added to the second slurry, preferably at a solid content of 25 wt% to 60 wt%, more preferably 30 wt% to 50 wt% or most preferably 35 wt% to 45 wt%. Subsequently, a combined slurry for preparing a catalytic functional system for reducing tailpipe ammonia emissions is formed by impregnating the support with the combined slurry, the combined slurry comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer.

[0141] In another preferred alternative embodiment of the method for preparing the exhaust gas treatment system of the present invention, a combined slurry comprising an ammonia oxidation catalyst (AMOx) from a first slurry and a selective catalytic reduction catalyst (SCR) from a second slurry is obtained by using a second slurry, wherein the metal-promoted zeolite of the selective catalytic reduction catalyst (SCR) is prepared by an in-slurry ion metal ion exchange method in the second slurry, the method comprising the steps of providing a slurry comprising a non-metal-promoted or metal-promoted zeolite, and exchanging the metal of the zeolite by ion exchange in the slurry to obtain a second slurry comprising the selective catalytic reduction catalyst (SCR) comprising the metal-promoted zeolite. Preferably, the particle size distribution D in the second slurry comprising the selective catalytic reduction catalyst (SCR) comprising the metal-promoted zeolite is 90In the range of 0.5 micron to 25 micron, preferably 1 micron to 20 micron, more preferably 2 micron to 15 micron and most preferably 3 micron to 8 micron. Optionally, zirconium oxide may be added to the second slurry, preferably at a solids content of 25 wt% to 60 wt%, more preferably 30 wt% to 50 wt% or most preferably 35 wt% to 45 wt%. It is also preferred in this preferred alternative process to obtain a particle size distribution D of a single combined slurry for use in a catalytically functional system for reducing tailpipe ammonia emissions. 90 The single combined slurry comprises an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support in the range of 2 microns to 50 microns, preferably 5 microns to 30 microns, more preferably 8 microns to 25 microns and most preferably 10 microns to 17 microns.

[0142] The final single-layer washcoat obtained by impregnation of the combined slurry, optionally after coating, drying (e.g. at 120° C. to 180° C.) and calcination (e.g. 400° C. to 600° C.) to obtain a catalytically functional system for reducing tailpipe ammonia emissions, preferably has a viscosity of 0.2 g / in 3 Up to 35g / in 3 , more preferably 0.5 g / in 3 Up to 15g / in 3 , even more preferably 0.8 g / in 3 Up to 5g / in 3 For example, 1.0 g / in 3 Up to 3.5g / in 3 or most preferably 1.5 g / in 3 Up to 2.5g / in 3 The total amount.

[0143] In the single-layer method, the loading of PGM on the support is typically 0.2 g / ft2 relative to the volume of the AMOx catalyst. 3 Up to 28g / ft 3 , more preferably 0.5g / ft 3 Up to 17g / ft 3 , even more preferably 1g / ft 3 Up to 8g / ft 3 , most preferably 2g / ft 3 Up to 5g / ft 3 .

[0144] A catalytic functional system for reducing tailpipe ammonia emissions, comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support, is applied to a suitable substrate, preferably a typical flow-through substrate. The substrate can typically be a monolithic piece. Preferably, the substrate has a honeycomb structure. Ceramic honeycomb substrates are particularly preferred.

[0145] According to a second alternative, the combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx) can be present as a zoned catalytic functional system, wherein the selective catalytic reduction catalyst (SCR) comprising a metal-promoted zeolite and the ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion (TWC) catalyst, are positioned in separate locations on a suitable support or carrier. The different zones for each catalytic functional system are positioned along the axial direction of the catalyst and substrate and / or the exhaust gas flow from the gasoline engine.

[0146] Preferably, a selective catalytic reduction catalyst (SCR) comprising a metal-promoted zeolite is carrier-coated at the inlet zone of the catalytic functional system for reducing tailpipe ammonia emissions, and preferably an ammonia oxidation catalyst (AMOx) comprising an additional three-way conversion (TWC) catalyst is carrier-coated at the outlet zone of the catalytic functional system for reducing tailpipe ammonia emissions.

[0147] Regarding the inlet zone, i.e. the first zone, a selective catalytic reduction catalyst (SCR) comprising a metal-supported zeolite can be selected and prepared similarly to the SCR catalyst used in the first alternative based on a single layer comprising a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx).

[0148] However, it is preferred to use lower amounts of selective catalytic reduction catalyst (SCR) comprising a metal-supported zeolite in the zoned process when compared to the alternative single layer process.

[0149] The inlet zone of the substrate in the zoned process can be coated with an SCR catalyst comprising a metal-supported zeolite according to established washcoat procedures familiar to those skilled in the art. A preferred option is to prepare a catalytic washcoat comprising an SCR catalyst comprising a metal-supported zeolite according to the description of the composition and preparation of SCR catalysts comprising metal-supported zeolites in the single-layer process given elsewhere herein.

[0150] Regarding the outlet zone, i.e. the second zone, an ammonia oxidation catalyst (AMOx) is coated to form a catalytic functional system for reducing tailpipe ammonia emissions, the ammonia oxidation catalyst preferably comprising a three-way conversion catalyst (TWC), the three-way conversion catalyst comprising at least one platinum group metal, an oxygen storage component (OSC) (preferably comprising ceria-zirconia) and optionally a promoter (preferably comprising barium oxide).

[0151] The outlet zone of the substrate in the zoned process may be coated with an ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion catalyst (TWC), according to established support coating procedures familiar to those skilled in the art.

[0152] A preferred option is to prepare a catalytic support coating comprising an ammonia oxidation catalyst (AMOx) comprising an additional three-way conversion catalyst (TWC) according to the description given elsewhere herein regarding the composition and preparation of an ammonia oxidation catalyst (AMOx) preferably comprising an additional three-way conversion catalyst (TWC) in a single-layer process.

[0153] For example, an ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion catalyst (TWC), may comprise at least one catalytically active metal, preferably platinum and / or rhodium, or alternatively palladium and / or rhodium, or even a combination of platinum and palladium and rhodium, on an alumina and / or ceria / zirconia support. In a preferred embodiment, platinum is supported on ceria-zirconia and rhodium or rhodium and platinum are supported on alumina, preferably lanthanum-doped alumina or ceria-alumina. The slurry for preparing the AMOx comprising the at least one catalytically active metal and the support material may not thermally fix the at least one platinum group metal on the support. Preferably, the slurry and the resulting support coating with AMOx also comprise typical promoters for better stability, preferably barium oxide. Preferably, the particle size distribution D in the slurry comprising the ammonia oxidation catalyst (AMOx) is 0.0447 W / cm2. 90 In the range of 1 to 45 microns, preferably 4 to 35 microns, more preferably 8 to 35 microns and most preferably 15 to 25 microns, the ammonia oxidation catalyst comprises an additional three-way conversion catalyst (TWC).

[0154] It is also preferred in the present invention that the particle size distribution D of the single combined slurry used in the catalytic functional system for reducing tail pipe ammonia emissions is obtained. 90 The single combined slurry comprises an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support in the range of 2 microns to 50 microns, preferably 5 microns to 30 microns, more preferably 8 microns to 25 microns and most preferably 10 microns to 17 microns.

[0155] In the zoned approach, the PGM loading on the support is typically 0.2 g / ft2 relative to the volume of the AMOx catalyst. 3 Up to 28g / ft 3 , more preferably 0.5g / ft 3 Up to 17g / ft 3 , even more preferably 1g / ft 3 Up to 8g / ft 3 , most preferably 2g / ft 3 Up to 5g / ft 3 .

[0156] In a zoned configuration, the total washcoat amount is preferably 0.2 g / in 3 Up to 35g / in 3 , more preferably 0.5g / in 3 Up to 15g / in 3 , even more preferably 0.8 g / in 3 Up to 5g / in 3 , such as 1.0g / in 3 Up to 3.5g / in 3 , or most preferably 1.5 g / in 3 Up to 2.5g / in 3 .

[0157] The present invention also relates to a method for treating an exhaust gas stream from a gasoline engine, comprising the steps of providing an exhaust gas stream comprising ammonia from a gasoline engine, and contacting the exhaust gas stream comprising ammonia with an exhaust gas treatment system according to the present invention to reduce ammonia emissions in the exhaust gas stream at the tailpipe. Example

[0158] Catalyst preparation and test description

[0159] Three-way conversion catalyst (TWC): 80g / ft 3 PtPdRh0 / 72 / 8

[0160] The technology uses a single-layer design consisting of Pd impregnated on high-porosity alumina. The main components of the slurry are high-porosity alumina and ceria-zirconia. Pd is impregnated on the latter, while Rh is supported on the former, using aqueous solutions of palladium nitrate and rhodium nitrate, respectively. The final dry Pd content is 72g / ft 3 , and the Rh content after drying is 8g / ft 3 In both cases (Pd or Rh), the process requires Pd or Rh impregnation on the selected support, followed by heat fixing of the PGM-containing frit (60% to 75% solids) at 400°C to 600°C for 2 to 4 hours.

[0161] Slurries were prepared from calcined PGM-containing glass frits using distilled water and a surfactant such as n-octanol under constant stirring. During slurry preparation, zirconium oxide and / or barium oxide were added using appropriate precursors in the range of 1 wt% to 4 wt% for zirconium oxide and 1 wt% to 10 wt% of total solids for barium oxide. The slurry solids content was adjusted (35% to 45%) to enhance pH and viscosity measurements as well as wet milling. After milling, the pH was adjusted with nitric acid (3.5 to 4.5). The slurry particle size distribution (Deo) was also measured after milling and fell within the range of 13 to 19 μm.

[0162] A ceramic honeycomb flow-through substrate (4.66 x 4.5", 600 / 4) was coated, dried in air (120°C to 180°C) and calcined (400°C to 600°C). The total washcoat loading was 2.8 g / in 3 Up to 3.5g / in 3 .

[0163] Four-way conversion catalyst (FWC): 10g / ft 3 PtPdRh0 / 8 / 2

[0164] The formulation used a single slurry containing Pd impregnated on high porosity alumina with a washcoat loading of 1.5 g / in3. The main components of the slurry were high porosity alumina and ceria-zirconia, with Pd impregnated on the latter and Rh loaded on the former using aqueous solutions of palladium nitrate and rhodium nitrate, respectively. The final dry Pd content was The Rh content after drying is 2g / ft 3 In both cases (Pd or Rh), the process requires Pd or Rh impregnation on the selected support, followed by heat fixing of the PGM-containing frit (60% to 75% solids) at 400°C to 600°C for 2 to 4 hours.

[0165] The calcined PGM-containing glass frit is made into a slurry using distilled water and a surfactant such as n-octanol under constant stirring. Zirconium oxide and / or barium oxide are added using appropriate precursors during the slurry preparation, with zirconium oxide ranging from 1 wt % to 4 wt %, and barium oxide total solids ranging from 1 wt % to 5 wt %. The slurry solids content is adjusted (35 wt % to 42 wt %) to enhance pH and viscosity measurements as well as wet grinding. After grinding, the pH is adjusted (3.2 to 4.0) with nitric acid. The slurry particle size distribution (D90) is also measured at the desired solids content before and after the slurry grinding (10 μm to 15 μm).

[0166] A ceramic honeycomb wall-flow substrate (4.66 x 4", 300 / 8) was coated, dried in air (120°C to 180°C) and calcined (400°C to 600°C).

[0167] Reference system (TWCUF): 4g / ft 3 0 / 3 / 1Pt / Pd / Rh

[0168] This technology comprises Pd and Rh on high-porosity alumina and ceria-zirconia supports, as well as barium oxide. It is a low-carrier, coated three-way catalyst for underfloor applications for HC, CO, and NOx purification. The main components of the slurry are high-porosity alumina and ceria-zirconia, with Pd impregnated onto the latter and Rh supported on the former using aqueous solutions of palladium nitrate and rhodium nitrate, respectively. The final dry Pd content is 3 g / ft 3 , while the Rh content after drying was 1 g / ft3. The slurry preparation involved wet impregnation of the precious metal on the selected support, followed by wet grinding after appropriate pH adjustment. The slurry solids content was also adjusted (35% to 45%) to enhance pH and viscosity measurements as well as wet grinding. After grinding, the pH was adjusted with nitric acid (3.5 to 5.0). The slurry particle size distribution (D90) was also measured after grinding and fell within the range of 12 μm to 22 μm.

[0169] A ceramic honeycomb flow-through substrate (5.66 x 3", 400 / 3) was coated, dried in air (120°C to 180°C) and calcined (400°C to 600°C). The total washcoat amount ranged from 1.5 g / in3 to 2.5 g / in3.

[0170] Example 1 of the present invention (SCR / AMOx): 4 g / ft 3 3 / 0 / 2Pt / Pd / Rh

[0171] The catalyst is a single slurry single layer design that combines PGM and zeolite in one slurry. Pt and Rh are sequentially impregnated at high solids content onto zirconia doped high porosity alumina and then thermally fixed. The slurry solids are in the range of 70% to 75%. The first slurry preparation step is completed when wet milling to a D90 in the range of 12 microns to 22 microns. The next step involves preparing a separate slurry with Cu-chabazite by stirring the zeolite in distilled water and adding zirconia with a solids content in the range of 35% to 45%. The zeolite slurry is dispersed to a D90 in the range of 3 microns to 8 microns by low energy mixing. The final slurry process requires blending the PGM-containing slurry and the zeolite slurry and then mixing thoroughly. The particle size distribution (D90) of the final slurry is in the range of 10 microns to 17 microns.

[0172] A ceramic honeycomb flow-through substrate (5.66 x 3", 400 / 3) was coated, dried in air (120°C to 180°C) and calcined (400°C to 600°C). The total washcoat amount ranged from 2.5 g / in3 to 3.5 g / in3.

[0173] Example 2 of the present invention (SCR / AMOx): 4 g / ft 3 4 / 0 / 0Pt / Pd / Rh

[0174] This catalyst is also a single slurry single layer design, which combines PGM and zeolite in one slurry. The difference from Example 1 of the present invention is that Rh is now replaced by Ti and Mn, which are sequentially impregnated on high porosity alumina with their respective precursors at a high solid content of 60% to 70% after Pt, and then thermally fixed. The catalyst is prepared by stirring and wet grinding to D in distilled water of appropriate pH. 90 The calcined powder was slurried to complete the first slurry preparation step by stirring the zeolite in distilled water and adding zirconium oxide with a solids content in the range of 35% to 45%. The zeolite slurry process differed from Example 1 in that the Cu exchange was performed during a slurry process called ISIE (Slurry In Ion Exchange). The zeolite slurry was dispersed to a PSD in the range of 3 microns to 8 microns by low energy mixing. 90 The final slurry process requires blending the PGM-containing slurry and the zeolite slurry and then mixing them thoroughly. The particle size distribution of the final slurry (D 90 ) in the range of 10 μm to 17 μm.

[0175] A ceramic honeycomb flow-through substrate (5.66 x 3", 400 / 3) was coated, dried in air (120°C to 180°C) and calcined (400°C to 600°C). The total washcoat amount was 1.0 g / in3 to 1.5 g / in3.

[0176] Example 3 of the present invention (SCR / TWC-AMOx): 3 g / ft 3 2 / 0 / 1Pt / Pd / Rh

[0177] This formulation was designed using a washcoat zoning concept, where the axial length is divided into two zones (inlet / outlet) to accommodate washcoats with different compositions and functions in specific zones along the axial length of the catalyst. The inlet zone contained Cu-chabazite, prepared like the zeolite slurry of Inventive Example 1. However, the amount of zeolite used was less than that of Inventive Example 1 (half the total zeolite in Inventive Example 1).

[0178] Cu-chabazite slurry (inlet SCR zone) was prepared by stirring Cu-chabazite in distilled water and adding zirconium oxide with a solid content ranging from 35% to 45%, followed by dispersion mixing.

[0179] The outlet zone contains Pt and Rh on high porosity alumina and ceria-zirconia supports. The latter component imparts oxygen storage capacity and enhances the three-way catalyst function. The slurry also contains barium oxide from a preferred precursor. Pt (50%) is impregnated on ceria-zirconia and PtRh is impregnated on lanthanum-doped high porosity alumina. This slurry does not involve thermal fixation of the PGMs and is primarily enhanced by a zoned carrier coating concept that mitigates negative zeolite / PGM interactions. The individual PGM frits are blended and diluted in distilled water at appropriate pH and solids content and then wet milled to D 90 PSD ranges from 15 microns to 25 microns.

[0180] A ceramic honeycomb flow-through substrate (4.66 x 3", 400 / 3) was coated with the Cu-zeolite slurry (50% inlet) and the PGM-containing slurry (50% outlet), dried (120°C to 180°C) and calcined (400°C to 600°C) in air. The total washcoat amount was 2.5 g / in 3 Up to 3.5g / in 3 .

[0181] Catalyst performance evaluation

[0182] The catalyst support described above is coated on a suitable substrate as described above. A close-coupled canister (CC) allows a three-way catalyst (TWC) coated on a flow-through substrate and a four-way catalyst (FWC) coated on a wall-flow substrate to be placed in the same canister, with the TWC closer to the engine. This canister is used upstream and serves different downstream components (see system layout).

[0183] The evaluated components were aged in an oven unit equipped with gas metering capabilities and flow meters, as well as thermocouples, at the inlet and internal sections. The furnace atmosphere consisted of 5% oxygen and 10% water (the remainder being N2), at a temperature of 820°C for 15 hours. All different components were placed in the same oven and exposed to the same air mass flow at the same temperature.

[0184] The system and corresponding component evaluations (WLTC) were performed on a Euro 6 GTDI vehicle using a chassis dyno test cell equipped with thermoelectric elements and FT-IR units at the engine outlet / catalyst inlet, catalyst bed, and outlet locations, allowing accurate recording of temperatures and gas emissions along the exhaust line.

Claims

1. An exhaust gas treatment system for reducing ammonia emissions from a gasoline engine, the exhaust gas treatment system comprising a three-way conversion catalyst (TWC) and a gasoline particulate filter (GPF), and further comprising a catalytic function system for reducing tailpipe ammonia emissions, characterized in that: The catalytic function system for reducing tailpipe ammonia emissions includes at least a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx).

2. The exhaust gas treatment system of claim 1, comprising a first three-way conversion catalyst (TWC) followed by a gasoline particulate filter (GPF) coated with a second three-way conversion catalyst (TWC).

3. The exhaust gas treatment system according to claim 1 or 2, wherein the three-way conversion catalyst and the gasoline particulate filter (GPF) are positioned upstream of the exhaust gas treatment system in a close-coupled (CC) position with the gasoline engine. 4 . The exhaust gas treatment system according to claim 1 , wherein the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined in one single layer on a substrate.

5. The exhaust gas treatment system according to any one of claims 1 to 4, wherein the ammonia oxidation catalyst (AMOx) comprises at least one catalytic metal on an alumina substrate.

6. Exhaust gas treatment system according to one of the preceding claims 1 to 5, wherein the ammonia oxidation catalyst (AMOx) comprises at least rhodium on a zirconium oxide-doped alumina support, preferably rhodium in combination with platinum and / or palladium on an alumina support.

7. The exhaust gas treatment system according to one of the preceding claims 1 to 5, wherein the ammonia oxidation catalyst (AMOx) does not contain any rhodium.

8. The exhaust gas treatment system according to one of the preceding claims 1 to 7, wherein the ammonia oxidation catalyst (AMOx) comprises titanium and / or manganese on an alumina support, preferably in combination with platinum and / or palladium.

9. The exhaust gas treatment system according to one of the preceding claims 1 to 8, wherein the selective catalytic reduction catalyst (SCR) comprises a metal-promoted, preferably copper- or iron-promoted, zeolite, preferably copper- or iron-promoted chabazite.

10. The exhaust gas treatment system according to any one of claims 1 to 9, wherein the catalytic function system for reducing tailpipe ammonia emissions comprises at least a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx), wherein the ammonia oxidation catalyst (AMOx) comprises a three-way conversion catalyst (TWC), wherein the three-way conversion catalyst comprises at least one platinum group metal, an oxygen storage component (OSC) preferably comprising ceria-zirconia, and optionally a promoter preferably comprising baria.

11. The exhaust gas treatment system according to any one of claims 1 to 3 and 5 to 10, wherein the catalytic functional system for reducing tailpipe ammonia emissions, which includes at least the combination of the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx), is a zoned catalytic functional system defined by the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx), the selective catalytic reduction catalyst comprises the metal-promoted zeolite carrier-coated at the inlet zone of the catalytic functional system for reducing tailpipe ammonia emissions, and the ammonia oxidation catalyst preferably comprises a three-way conversion (TWC) catalyst carrier-coated at the outlet zone of the catalytic functional system for reducing tailpipe ammonia emissions.

12. The exhaust gas treatment system according to claim 11, wherein the washcoat comprising the ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion catalyst (TWC), is prepared from a slurry comprising the at least one platinum group metal on a support without a step of thermally fixing the platinum group metal on the support.

13. A method for preparing an exhaust gas treatment system according to any one of claims 5 to 13, the method comprising the following steps: - Provides a three-way conversion catalyst (TWC) and a gasoline particulate filter (GPF), - preparing a first slurry comprising said ammonia oxidation catalyst (AMOx) by impregnating at least one catalytically active metal on an alumina support, - preparing a second slurry comprising said selective catalytic reduction catalyst (SCR) containing a metal-promoted zeolite, - blending the first slurry and the second slurry to obtain a combined slurry comprising the ammonia oxidation catalyst (AMOx) from the first slurry and the selective catalytic reduction catalyst (SCR) from the second slurry, - impregnating a support with the combined slurry to obtain the catalytically functional system for reducing the tailpipe ammonia emissions, the catalytically functional system comprising the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR) combined in a single layer on the support, and - positioning the catalytic functional system for reducing the tailpipe ammonia emission, comprising the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR), downstream of the three-way conversion catalyst (TWC) and the gasoline particulate filter (GPF).

14. The method of claim 13, wherein the second slurry comprising the selective catalytic reduction catalyst (SCR) is prepared by providing a slurry comprising a non-metal-promoted or metal-promoted zeolite, and performing metal exchange of the zeolite by ion exchange in the slurry to obtain the second slurry comprising the selective catalytic reduction catalyst (SCR) containing the metal-promoted zeolite.

15. A method of treating an exhaust gas stream from a gasoline engine, said method comprising the steps of: An exhaust gas stream comprising ammonia from a gasoline engine is provided and brought into contact with an exhaust gas treatment system according to one of the preceding claims 1 to 13 in order to reduce ammonia emissions in the exhaust gas stream at the tailpipe.

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