Ammonia Oxidation Catalyst with Zoned 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 including a three-way catalyst (TWC) and a gasoline particulate filter (GPF), and further including a catalytic function for reducing tailpipe ammonia emissions, the catalytic function for reducing tailpipe ammonia emissions including at least a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx). The present invention also relates to methods for preparing the exhaust gas treatment system and for treating an exhaust gas stream from a gasoline engine using the exhaust gas treatment system of the present invention.

Description

[Technical Field]

[0001] The present invention relates to the field of exhaust gas treatment systems for automotive applications, particularly those suitable for gasoline engines. The present invention particularly relates to a catalyst and method for removing ammonia emissions from exhaust gas streams generated by gasoline engines. [Background technology]

[0002] The Euro 6 regulations require the removal of nitrogen oxides (NOx), unburned hydrocarbons (HC) and carbon monoxide (CO) from the exhaust gas stream of vehicle engines. They also require reductions in particulate emissions to be achieved.

[0003] These requirements have been met by the introduction of three-way conversion catalysts (TWCs), which have been effective in removing nitrogen oxides, hydrocarbons, and carbon monoxide, while three-way conversion catalysts (TWCs), optionally combined with a filtering function, e.g., four-way conversion catalysts (FWCs), have been further developed for the effective removal of particulates.

[0004] As a result, three-way catalysts (TWC) and four-way catalysts (FWC) are widely used in the treatment of 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, political efforts towards climate neutrality based on the zero-pollution ambitions of the European Green Deal will lead to further developments in emissions regulations. Even stricter EURO7 emission standards are currently being developed, which will require further developments in exhaust gas treatment systems in the automotive sector.

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

[0007] In this regard, one of the unresolved issues with currently used exhaust gas treatment systems arises from potential "ammonia slip" from SCR catalysts, where ammonia injection is used to purge NOx. Furthermore, even in exhaust gas treatment systems without an ammonia injection system, ammonia can form in gasoline engine exhaust gases via several pathways when hydrogen gas reacts with some nitrogen oxides to form ammonia. Hydrogen is generated on precious metal sites during the so-called water-gas shift reaction, which is facilitated by periodic exhaust treatment, as in gasoline applications. These pathways include when hydrocarbons react with water to form hydrogen, reactions from carbon monoxide and steam, and / or reactions via steam reforming at temperatures above 350 °C. For example, nitric oxide (NO) and nitrogen dioxide (NO2) can react in the presence of hydrogen to produce ammonia.

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

[0009] Therefore, to significantly reduce ammonia tailpipe emissions in future vehicles based on the expected future EURO7 regulations and the conventional currently used three-way catalysts (TWCs) with filtering functionality, it is necessary to complement existing exhaust gas treatment systems with an additional ammonia purge function. Summary of the Invention

[0010] A further important objective is to establish a good balance in a conventional three-way catalyst with particulate filtering functionality in the presence of additional ammonia removal functionality to achieve coordinated removal of all relevant pollutants including nitrogen oxides (NOx), unburned hydrocarbons (HC), carbon monoxide (CO), particulates and ammonia (NH3).

[0011] A further objective of the catalyst configuration is the stability of the exhaust gas treatment system over time during long-term operation at high temperatures, as typically observed in gasoline engines with alternating lean / rich cycles and relatively high engine temperatures. Therefore, aging stability during long-term operation at high engine temperatures is an important requirement for any catalyst configuration to be used in exhaust gas treatment systems for gasoline engines. A further objective is to achieve the removal of relevant pollutants with a catalyst configuration that applies all of the necessary catalytic functions in amounts less than absolutely necessary. Most catalytic functions involve expensive components, such as platinum group metals or zeolites, and require laborious preparation, posing the challenge of using only limited amounts of such valuable components in the relevant catalyst.

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

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

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

[0015] In another preferred embodiment, the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined in one 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 zirconia 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) is rhodium-free.

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

[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 zeolite.

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

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

[0023] In another preferred embodiment, a washcoat comprising an ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way 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, there is provided a method for preparing an exhaust gas treatment system, the method comprising: providing a three-way catalyst (TWC) and a gasoline particulate filter (GPF); - 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) comprising a metal-promoted zeolite; - blending the first slurry and the second slurry to obtain a combined slurry comprising an ammonia oxidation catalyst (AMOx) from the first slurry and a selective catalytic reduction catalyst (SCR) from the second slurry; - impregnating a support with the combined slurry to obtain a catalytic function for reducing tailpipe ammonia emissions, comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on the support; - disposing a catalytic function for reducing tailpipe ammonia emissions, including an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR), downstream of the three-way catalyst (TWC) and gasoline particulate filter (GPF).

[0025] 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 in the slurry by ion exchange to obtain a second slurry comprising a selective catalytic reduction catalyst (SCR) comprising a metal-promoted zeolite.

[0026] In a third aspect of the present invention, there is provided a method of treating an exhaust gas stream of a gasoline engine, the method comprising the steps of providing an exhaust gas stream from the gasoline engine comprising ammonia, 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. [Brief explanation of the drawings]

[0027] [Figure 1]Various configurations of catalysts in exhaust gas systems for gasoline engines are shown. The first configuration shown in FIG. 1 is a comparative control system and includes a conventional TWC function in this specification combined with an upstream gasoline particulate filter (GPF), followed downstream by another TWC catalyst in an underfloor location that is barely sufficient to purge significant amounts of ammonia. The next three configurations in FIG. 1 are in accordance with the present invention, again including a conventional TWC function in this specification combined with an upstream gasoline particulate filter (GPF), followed by three different inventive SCR / AMOx functions downstream of the TWC / GPF function. The catalysts of the four configurations were oven-aged for 15 hours at an internal oven temperature of 820°C under specific gas compositions. The second and third configurations in FIG. 1 (the first and second inventive configurations, similar to Inventive Examples 1 and 2, respectively) may have some differences. In the second configuration (the first inventive configuration), the platinum group metal and zeolite are used in one slurry to achieve a single-slurry, single-layer design for the SCR / AMOx function. In the third configuration, i.e., the second inventive configuration, the platinum group metal and zeolite can be applied in one slurry under the same preparation conditions to the same ceramic honeycomb flow-through substrate, preferably with a slightly different total washcoat amount, resulting in a single-slurry, single-layer design on the substrate. Furthermore, in contrast to the second configuration (first inventive configuration), the third configuration (second inventive configuration) can be derived from a different zeolite slurry process, resulting from a so-called "in-slurry ion exchange" approach, in which Cu exchange occurs during the slurry process. Another difference in the third configuration (second inventive configuration) of Figure 1 can be that the platinum group metal rhodium (Rh) is replaced by titanium (Ti) and manganese (Mn).The fourth configuration of FIG. 1 (the third configuration of the present invention, similar to Example 3 of the present invention) differs from all other configurations by having a conventional TWC / GPF function located upstream followed by an SCR / AMOx function for ammonia removal arranged in a zone configuration, with the SCR and TWC / AMOx catalytic functions presented in separate locations on the ceramic honeycomb flow-through substrate downstream of the TWC / GPF function. [Figure 2] Figure 2 shows the carbon monoxide (CO) tailpipe emissions over time observed for the four configurations described in Figure 1. In the diagram of Figure 2, the speeds applied in a Euro 6 GTDI vehicle with chassis dyno test cell are also shown for further comparison of the four catalyst configurations. [Figure 3] Figure 3 shows the tailpipe emissions of nitrogen oxides (NOx) over time observed for the four configurations described in Figure 1. In the diagram of Figure 3, the speeds applied in a Euro 6 GTDI vehicle with chassis dyno test cell are also shown for further comparison of the four catalyst configurations. [Figure 4] Figure 4 shows the tailpipe emissions of ammonia (NH3) over time observed for the four configurations described in Figure 1. In the diagram of Figure 4, the applied speeds in a Euro 6 GTDI vehicle with chassis dyno test cell are also shown for further comparison of the four catalyst configurations. DETAILED DESCRIPTION OF THE INVENTION

[0028] The exhaust gas treatment system of the present invention will be described in more detail below.

[0029] As used herein, terms such as "catalyst," "catalytic function," "catalytic component," "catalytic material," and the like refer to a material that promotes a reaction or several reactions. Thus, the present invention generally features the combination of several catalytic functions in one exhaust gas treatment line for the synergistic removal of several pollutants simultaneously from the tailpipe.

[0030] The individual catalytic functions 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. The exhaust gas treatment system of the present invention includes a three-way catalyst (TWC) downstream of the gasoline engine. The three-way catalyst (TWC) is preferably located in close proximity to the gasoline engine, typically in a close-coupled position. More preferably, there are no other catalytic functions located between the gasoline engine outlet and the three-way catalyst (TWC), and the three-way catalyst (TWC) is the first catalytic function of the exhaust gas treatment system of the present invention located after the gasoline engine outlet.

[0031] 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 location of a catalytic function or component as compared to the relative location of another catalytic function or component within the exhaust gas system (or a gasoline engine) based on the flow direction of the exhaust gas stream.

[0032] The term "close coupled" refers to a location that is in fluid communication with and immediately downstream of an engine outlet, preferably a gasoline engine outlet, and is preferably located 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 as commonly understood in the art, e.g., substantially closer to the engine than a conventional "underfloor" location (under the floor of the vehicle). Generally, but not exclusively, such a "close coupled" location is preferably in the engine compartment adjacent to the exhaust manifold, usually under the hood of the vehicle.

[0033] Thus, a three-way catalyst (TWC) located in a "close coupled" position is generally exposed to the hot exhaust gases that are immediately emitted from the engine after it has warmed up, and therefore often acts to reduce hydrocarbon emissions during a cold start (which is typically the period immediately after starting the engine from ambient conditions).

[0034] The three-way catalyst of the present invention will be described in more detail below.

[0035] In its most general embodiment, the TWC catalyst should provide the common essential components of a TWC catalyst suitable for removing the three major pollutants generated by a gasoline engine, including, but not limited to, unburned hydrocarbons (HC), nitrogen oxides (NOx), and carbon monoxide (CO).

[0036] Therefore, the composition of the three-way conversion catalyst coating is selected to include a hydrocarbon (HC) oxidizing component, a carbon monoxide (CO) oxidizing component, and a nitrogen oxide (NOx) reducing component that enables purging of NOx, HC, and CO from the exhaust gas stream of the gasoline stream.

[0037] The three-way 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 in the catalyst with a suitable support material, typically a refractory metal oxide support. The combination of at least one platinum group metal (PGM) with a refractory metal oxide support can be important for achieving high catalytic performance and excellent stability in terms of extended aging at high temperatures.

[0038] The entire TWC catalyst is disposed on a suitable support material, which is defined in more detail below, that allows the TWC catalyst to be disposed in the most suitable manner in the exhaust gas treatment line of the vehicle.

[0039] Thus, a preferred three-way catalyst (TWC) of the present invention for the treatment of exhaust gas streams 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 support, wherein the platinum group metal (PGM) preferably comprises at least one platinum group metal selected from platinum, palladium and rhodium. One preferred combination of the at least one platinum group metal is palladium and rhodium, or platinum and rhodium, or a combination of three platinum group metals, platinum, palladium and rhodium, or platinum and palladium alone.

[0040] Furthermore, additional platinum group metals (PGMs) other than platinum, palladium, and rhodium may optionally be present. For example, additional platinum group metals (PGMs) such as ruthenium, osmium, and / or iridium may optionally be present in the three-way catalysts (TWCs) of the present invention.

[0041] When the at least one platinum group metal in the three-way catalyst comprises platinum and palladium, the weight ratio of platinum to palladium in the three-way catalyst (TWC), based on the total weight of the platinum group metals (PGMs), is preferably 5:95 to 45:55, the refractory metal oxide support is preferably selected from a mixture or mixed oxide of ceria and alumina, or a lanthana-doped alumina containing lanthana in an amount of up to 10 wt. % based on the weight of the lanthana-doped alumina, and more preferably such a three-way catalyst (TWC) is in a close-coupled position relative to the engine outlet.

[0042] Even more preferably, the TWC is in fluid communication with and immediately downstream of the engine outlet, preferably the gasoline engine outlet. Most preferably, the TWC of the present invention is located within 50 cm, more preferably within 30 cm, and most preferably within 20 cm after the engine outlet. It is also particularly preferred that the TWC is not in an underfloor location, i.e., not under the floor of the vehicle.

[0043] In other words, the TWC is located in a close-coupled position within the engine compartment, preferably under the hood of the vehicle adjacent to the exhaust manifold. Thus, a TWC located in a "close-coupled" position is generally exposed to the hot exhaust gases that are immediately exhausted from the engine after the engine has warmed up, and therefore often acts to reduce hydrocarbon emissions during a cold start (which is typically the period immediately after starting the engine from ambient conditions).

[0044] The total loading of platinum group metal (PGM) components supported on a refractory metal oxide support in the three-way catalyst (TWC) of the present invention is preferably from 1 to 200 g / ft 3 More preferably, in the range of 20 to 180 g / ft 3 and even more preferably in the range of 50 to 150 g / ft 3 in the range of 70 to 125 g / ft 3 Generally, those skilled in the art will be familiar with determining the loading of platinum group metals (PGMs) on a catalyst coating. For example, X-ray fluorescence (XRF) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) can be used to measure the catalyst loading of platinum group metals (PGMs).

[0045] The three-way catalyst (TWC) of the present invention comprises a refractory metal oxide support. The refractory metal oxide support is essential to the present invention and is combined with the platinum group metal (PGM) component in the catalyst of the present invention. Preferably, the refractory metal oxide support is non-zeolitic.

[0046] One preferred refractory metal support material comprises a mixture or mixed oxide of cerium oxide and aluminum oxide, preferably having a weight ratio of ceria to alumina of 10:90 to 90:10, or 25:75 to 75:25, or 30:70 to 70:30, more preferably 40:60 to 60:40, and even more preferably 45:55 to 55:45.

[0047] Another preferred refractory metal support material is alumina, particularly highly porous alumina. Particularly preferred is aluminum oxide doped with lanthana (such as La2O3). Lantana-doped alumina refers to alumina containing a significant amount of lanthana, preferably at most 10% by weight, more preferably at most 7% by weight, even more preferably at most 5% by weight, and most preferably at most 4% by weight, based on the weight of the lanthana-doped alumina. La-doped alumina (L-doped alumina) contains at least 0.5% by weight, more preferably at least 1% by weight, and most preferably at least 2% by weight, based on the weight of the lanthana-doped alumina.

[0048] The aluminum oxide used in the refractory metal oxide support material of the present invention may preferably be stabilized aluminum oxide. The aluminum oxide of the refractory metal oxide support may preferably be gamma aluminum oxide. The refractory metal oxide support of the three-way catalyst (TWC) of the present invention may optionally contain additional metal oxides such as zirconia, ceria, baria, and / or neodymia.

[0049] The total loading of the refractory metal oxide support in the three-way catalyst (TWC) of the present invention is preferably 0.2 to 6.0 g / in 3 in the range of 0.5 to 5.0 g / in 3 in the range of 1.0 to 4.0 g / in 3 and even more preferably in the range of 2.5 to 3.5 g / in 3 The range is.

[0050] The ceria content in the three-way catalyst (TWC) of the present invention is preferably 0.4 to 4.0 g / in 3 in the range of 0.7 to 3.0 g / in 3 and even more preferably in the range of 0.9 to 2.0 g / in 3 or most preferably in the range of 1.0 to 1.5 g / in 3 The range is.

[0051] More preferably, the refractory metal oxide support has a porosity in the range of 0.05 to 1.5 mL / g, more preferably in the range of 0.1 to 1.0 mL / g, more preferably in the range of 0.15 to 0.8 mL / g. The porosity of the refractory metal oxide support is determined by N2 physisorption and analysis of the physisorption isotherm by BJH (Barett, Joyner, Halenda) analysis according to DIN 66134.

[0052] The three-way catalyst (TWC) preferably includes an additional oxygen storage component (OSC) and / or promoter component. Those skilled in the art will understand the technical role that the additional oxygen storage component (OSC) and / or promoter component typically plays in a three-way catalyst.

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

[0054] More preferably, the oxygen storage compound contains cerium, and even more preferably, it contains one or more of cerium oxide, a mixture of oxides containing cerium oxide, and a mixed oxide containing cerium, where the mixed oxide containing cerium preferably further contains one or more of zirconium, yttrium, neodymium, lanthanum, and praseodymium, more preferably one or more of zirconium, yttrium, neodymium, and lanthanum, more preferably zirconium, yttrium, neodymium, and lanthanum. Furthermore, the cerium-containing oxygen storage compound may be composed of two or more different mixed oxides, each of which may contain 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.

[0055] The oxygen storage compound has a preferred porosity in the range of 0.05 to 1.5 mL / g, more preferably in the range of 0.1 to 1.0 mL / g, and more preferably in the range of 0.15 to 0.8 mL / g. The porosity of the oxygen storage compound is determined by N2 physical adsorption and analysis of the physical adsorption isotherm by BJH (Barett, Joyner, Halenda) analysis according to DIN 66134.

[0056] The three-way catalyst (TWC) preferably comprises an additional promoter component. The term "promoter" as used in the context of the present invention relates to a compound that enhances the overall catalytic activity and / or contributes to the stability of the three-way catalyst.

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

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

[0059] As used herein, a washcoat layer comprises layers of compositionally distinct materials disposed on the surface of a monolithic substrate or, optionally, an underlying washcoat layer, as described in Heck, Ronald and Farrauto, Robert, Catalytic Air Pollution Control, New York: Wiley-Interscience, 2002, pp. 18-19. Washcoats are typically composed 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.

[0060] Preferably, the three-way catalyst (TWC) is in the form of one or several washcoats, preferably in the form of 0.5 to 5 g / in 3 in the range of 1.5 to 4.5 g / in 3 in the range of 2.0 to 4.0 g / in 3 in the range of 2.7 to 3.5 g / in 3 The carrier is present at a total loading in the range of 0.1 to 1.0 wt.

[0061] The three-way catalyst of the present invention can have a single washcoat layer containing at least one platinum group metal (PGM) on a support material. For example, palladium can be impregnated on ceria-zirconia. In addition, rhodium can be further included in a single washcoat layer containing palladium as a platinum group metal supported on ceria-zirconia, and rhodium can be further supported on highly porous alumina to form a preferred single washcoat layer containing palladium supported on ceria-zirconia and rhodium supported on alumina. Promoter compounds such as zirconia and / or barrier can optionally be added to the preferred single-layer design of the three-way catalyst (TWC).

[0062] Alternatively, a three-way catalyst (TWC) can include two or more washcoat layers, particularly two washcoat layers including a bottom washcoat and a top washcoat. Each washcoat layer can have a unique chemical catalytic function depending on its exact composition. The bottom washcoat (or first coating) is applied onto the substrate, and the top washcoat (or second coating) is applied onto the bottom washcoat.

[0063] As far as the bottom washcoat or first washcoat (or first coating) is concerned, 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 along with palladium and / or platinum. In one preferred embodiment, the bottom washcoat may include palladium as the only platinum group metal (PGM), in the absence of platinum and rhodium. Alternatively, platinum and palladium are combined in the bottom washcoat in the absence of other platinum group metals (PGMs).

[0064] Optionally, in the absence of platinum and rhodium, palladium can be combined with other platinum group metals (PGMs) such as ruthenium, osmium and / or iridium in the bottom washcoat.

[0065] The platinum group metal (PGM) component of the bottom washcoat is supported on a refractory metal oxide support. Preferably, the refractory metal oxide support of the bottom washcoat is non-zeolitic. The refractory metal oxide support of the bottom washcoat preferably comprises a mixture of aluminum oxide and cerium oxide. Another preferred refractory metal support material for the bottom washcoat comprises lanthanum-doped aluminum oxide. The aluminum oxide used in the refractory metal oxide support material may preferably be stabilized aluminum oxide. The aluminum oxide of the refractory metal oxide support of the bottom washcoat may also preferably be gamma aluminum oxide. The refractory metal oxide support of the bottom washcoat may optionally comprise additional metal oxides such as zirconia, ceria, baria, and / or neodymia.

[0066] Another preferred refractory metal support material for the bottom washcoat comprises a mixture or mixed oxide of cerium oxide and aluminum oxide. Preferably, the mixture or mixed oxide of ceria and alumina has a weight ratio of ceria to alumina of 10:90 to 90:10, 25:75 to 75:25, or 30:70 to 70:30, more preferably 40:60 to 60:40, and even more preferably 45:55 to 55:45.

[0067] Another preferred refractory metal support material for the bottom washcoat comprises aluminum oxide doped with lanthana (such as La2O3). Lantana-doped alumina refers to alumina containing a significant amount of lanthana, 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.%, based on the total weight of the lanthana-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.%, based on the total weight of the lanthana-doped alumina.

[0068] As far as the top washcoat or second washcoat (or second coating) is concerned, a combination of rhodium and palladium is preferably added as a platinum group metal (PGM), preferably in the absence of platinum. Other platinum group metals, such as ruthenium, osmium, and / or iridium, may optionally be present along with the rhodium and palladium. In one preferred embodiment, the top washcoat may further comprise rhodium as the only platinum group metal (PGM), in the absence of platinum and palladium. 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 coating with other platinum group metals (PGM), such as ruthenium, osmium, and / or iridium.

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

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

[0071] Another preferred refractory metal support material for the top washcoat comprises aluminum oxide doped with lanthanum, such as lanthana (e.g., La2O3). Lantana-doped alumina refers to alumina containing a significant amount of lanthana, 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.%, based on the weight of the lanthana-doped alumina. La-doped alumina contains at least 0.5 wt.%, more preferably at least 1 wt.%, and most preferably at least 2 wt.%, based on the weight of the lanthana-doped alumina.

[0072] A typical exhaust gas treatment system according to the present invention includes a three-way catalyst (TWC) and a gasoline particulate filter function. In a preferred embodiment, the exhaust gas treatment system of the present invention includes a first three-way catalyst (TWC) followed by a gasoline particulate filter (GPF) coated with a second three-way catalyst (TWC). For example, the first three-way catalyst (TWC) is in a close-coupled position with respect to the engine, followed downstream by a gasoline particulate filter (GPF) coated with a second three-way catalyst (TWC), which is preferably in a close-coupled position with respect to the first three-way catalyst (TWC).

[0073] The gasoline particulate filter (GPF) of the exhaust gas treatment system of the present invention may be a coated filter or a bare filter. If the gasoline particulate filter (GPF) is not a coated filter, i.e., if it is a bare or bare filter, there is no catalytically active coating on the filter medium. That is, particles from the exhaust gas stream are retained in the pores of the filter medium depending on their size and purged, but chemical catalytic conversion does not occur in the filter medium of a 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 generated by a gasoline engine and carried over into the exhaust gas stream purged by the exhaust gas treatment system of the present invention. Coated filters (CFs) have a filter as an essential feature suitable for capturing particulate matter from the exhaust gas stream based on the presence of a porous medium through which the exhaust gas stream can flow while the particulate matter is retained in the pores. Applying a coated filter is preferable to limit backpressure on the exhaust gas stream. That is, the porous media having a filtering function can be coated with a catalytically active material that optionally contributes to the conversion of pollutants from the exhaust gas stream flowing through the filter media. Particles trapped in the filter pores are combusted into carbon dioxide at high temperatures and / or with the further assistance of a catalytic coating. In this regard, the catalytically active coating on the coated filter (CF) preferably contributes to preventing pore clogging and backpressure buildup typically caused by particulate accumulation in the pores of the coated filter. A preferred catalytic coating on the coated filter of a gasoline particulate filter (GPF) is a three-way catalyst (TWC), as described elsewhere herein. Thus, the coated filter (CF) preferably provides a second three-way catalyst (TWC) function in the exhaust gas treatment system of the present invention. One possible coated filter (CF) is a four-way catalyst (FWC), which is more preferably located in close proximity to the three-way catalyst (TWC), e.g., in a close-coupled position relative to the first three-way catalyst (TWC).As those skilled in the art will appreciate, a coated filter (CF) including a second three-way catalyst (TWC), such as a four-way catalyst (FWC), integrates a typical three-way catalyst (TWC) function with an additional particulate removal function. Thus, the exhaust gas treatment system of the present invention can preferably combine two three-way catalyst (TWC) functions, and more preferably, the downstream-located second TWC further includes a catalytic function for removing particulate matter, for example, due to the presence of a filter, preferably a gasoline particulate filter (GPF).

[0074] If the particulate filter is a coated particulate filter, it is used as a substrate on which a second three-way catalyst (TWC) can be coated on the surface or pores of the particulate filter. As already described in more detail above for three-way catalysts (TWC), the second three-way catalyst (TWC) function of the coated filter (CF), preferably a four-way catalyst (FWC), can be present in the form of one single washcoat or several washcoats, for example two different washcoats or coatings.

[0075] Capture of particulate matter in a gasoline particulate filter (GPF) can be achieved, for example, by the use of a particulate (or soot) filter, or by the use of a flow-through substrate having an internal serpentine path so that a change in direction of flow of the particulates causes them to drop out of the exhaust stream. A typical monolithic substrate has narrow, parallel gas passages extending from the inlet or outlet face of the substrate, thereby opening the passages for fluid flow therethrough (a "flow-through substrate").

[0076] The flow-through substrate may be a monolithic substrate, including a flow-through honeycomb monolithic substrate. Those skilled in the art are familiar with flow-through substrates, which generally have narrow, parallel gas flow passages extending from the inlet end to the outlet end of the substrate such that the passages are open to fluid flow. The passages are essentially linear paths from the fluid inlet to the fluid outlet and are defined by walls on which a catalytic coating may be disposed so that gas flowing through the passages contacts the catalytic material. The passages in a flow-through substrate are thin-walled channels and may be of any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, or circular. The flow-through substrate may be ceramic or metallic, as further described below. The flow-through substrate may, for example, have a volume of about 50 in 3 ~About 1200in 3 , with a cell density (inlet opening) of about 60 cells per square inch (cpsi) to about 1200 cpsi, or about 200 to about 900 cpsi, or for example about 300 to about 600 cpsi, and a wall thickness of about 50 to about 400 microns, or about 100 to about 200 microns.

[0077] Suitable substrates are preferably ceramic substrates made from any suitable refractory material, such as cordierite, cordierite-alpha alumina, aluminum titanate, silicon titanate, silicon carbide, silicon nitride, zircon mullite, spodumene, alumina-silica-magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alpha alumina, aluminosilicate, and the like.

[0078] The most preferred substrate in the present invention is wall flow filter substrate.As those skilled in the art will understand, wall flow filter substrate has a plurality of thin, substantially parallel gas flow passages extending along the longitudinal axis of the substrate, and typically each passage is blocked at one end of the substrate body, and alternate passages are blocked at the opposite end face ("wall flow filter").Suitable flow-through substrates and wall flow substrates are also taught, for example, in WO2016 / 070090, which is incorporated herein by reference in its entirety.

[0079] Preferably, the wall flow filter substrate comprises, and more preferably consists of, cordierite, silicon carbide, aluminum titanate, or a combination thereof.

[0080] Preferably, in a gasoline particulate filter (GPF) optionally including a second three-way conversion (TWC) function, more preferably a four-way conversion catalyst, the three-way conversion function is present on the particulate filter by permeating through the wall of the particulate filter function. In this preferred embodiment, there is no layer of three-way conversion catalyst material on the surface of the wall of the particulate filter function of the gasoline particulate filter (GPF). More preferably, in this preferred configuration, the resulting four-way conversion catalyst including the particulate filter function has a coated porosity that is smaller than that of the bare particulate filter. More preferably, the coated porosity may be 75-98% of the uncoated porosity, or the coated porosity may be 80-95% of the uncoated porosity, or the coated porosity may be less than 80-93% of the uncoated porosity.

[0081] The gasoline particulate filter (GPF) may preferably include a catalytically active coating that includes a three-way catalyst (TWC) function. The three-way catalyst (TWC) coating, preferably a four-way catalyst (FWC), of the coated filter (CF) may preferably be formed from a single washcoat composition that permeates the inlet side, the outlet side, or both the inlet and outlet sides of the particulate filter.

[0082] Alternatively, several three-way catalyst (TWC) coatings, preferably two coatings, of a coated filter (CF), preferably a four-way catalyst (FWC), can be formed from several, preferably two, washcoat compositions. Different washcoat compositions can be applied to penetrate the inlet and outlet sides. Alternatively, one single washcoat composition or several washcoat compositions can be applied to the inlet and outlet sides of the particulate filter.

[0083] The catalytically active coating of three-way catalyst (TWC) material on the coated filter (CF) is about 1 to about 5 g / in 3 (about 60 to about 300 g / L). The uncoated porosity may be in the range of 55 to 70%. More preferably, the coated filter (CF) has a porosity of 120 to 244 g / L (about 1.0 to about 4.0 g / in). 3 ), and a porosity in the range of 55-70%, with the particulate filter functioning having a wall thickness in the range of about 152 μm (6 mils) to about 356 μm (14 mils). In this embodiment, the three-way catalyst (TWC) permeates the walls of the particulate filter, while no layer of catalyst material is present on the surface of the particulate filter walls. Preferably, no three-way catalyst material is present outside the pores of the particulate filter walls.

[0084] Certain coated filters (CFs), preferably four-way conversion catalysts, and their preparation are described in WO 2019 / 149929(A1), WO 2019 / 149930(A1) and WO 2020 / 043885(A1), all of which are incorporated herein by reference in their entireties.

[0085] A coated particulate filter (CF), preferably a four-way catalyst (FWC), can be prepared by applying a three-way catalyst (TWC) coating onto a particulate filter as follows: The method involves providing a suitable particulate filter substrate, forming a slurry of three-way conversion (TWC) catalyst material having a pH in the range of 2 to 7, and infiltrating the TWC catalyst material into the walls of the particulate filter to form a coated filter (CF), preferably a four-way conversion catalyst (FWC), having particulate filtering capabilities, such that the coated filter (CF) has a coated porosity that is less than the uncoated porosity of the particulate filter. The slurry may have a dynamic viscosity in the range of about 5 to less than 40 mPas at 20°C and a solids content of 0 to 25% by weight solids. The pH may be in the range of 3 to 5. Preferably, there is no layer of catalyst material on the surface of the particulate filter walls, except optionally in the area of ​​the overlapping washcoat. In a preferred embodiment, there is no catalyst material outside the pores of the particulate filter walls. The coated porosity may be linearly proportional to the washcoat loading of the TWC catalyst material. The coated porosity may be 75-98% of the uncoated porosity, or even 80-95%, or even 80-93% of the uncoated porosity. Preferably, the particulate filter may have 200-300 cells per square inch (OPSI) and a wall thickness in the range of 6-14 mils.

[0086] To address the objective of further reducing ammonia emissions from gasoline engines, the three-way catalyst (TWC) and coated filter (CF), preferably the four-way catalyst (FWC), of the exhaust gas treatment system of the present invention is combined with an appropriate catalytic function to reduce tailpipe emissions of ammonia. The present invention achieves such objective by including at least a combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx).

[0087] 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 one first alternative, the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined together in one 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 function in which the selective catalytic reduction catalyst (SCR) containing a metal-promoted zeolite and the ammonia oxidation catalyst (AMOx), preferably containing an additional three-way conversion (TWC) catalyst, are disposed in separate locations on a suitable carrier or support. Preferably, the selective catalytic reduction catalyst (SCR) containing a metal-promoted zeolite is washcoated in the inlet zone of the catalytic function for reducing ammonia tailpipe emissions, and the ammonia oxidation catalyst (AMOx), preferably containing an additional three-way conversion (TWC) catalyst, is washcoated in the outlet zone of the catalytic function for reducing ammonia tailpipe emissions.

[0088] The SCR catalyst used in the present invention can include, for example, one or more metal oxides (eg, mixed oxides), molecular sieves (preferably metal-promoted molecular sieves), or combinations thereof.

[0089] The SCR catalyst preferably comprises one or more molecular sieve materials. More preferably, the SCR catalyst material comprises an 8-ring small pore molecular sieve containing a metal promoter. As used herein, "small pore" refers to a pore opening smaller than about 5 angstroms (e.g., about 2-5 Å, about 2-4 Å, about 3-5 Å, or about 3-4 Å, e.g., on the order of about 3.8 Å). One particularly preferred 8-ring small pore molecular sieve is an 8-ring small pore zeolite.

[0090] The SCR catalyst material preferably comprises a zeolite, preferably a zeolite containing d6r units. Thus, the SCR catalyst material can comprise a zeolite having a structure type selected from 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 catalyst materials comprise zeolites having a structure type selected from the group consisting of CHA, AEI, AFX, ERI, KFL, LEV, and combinations thereof. Particularly preferred SCR catalyst materials comprise zeolites having a structure type selected from CHA and AEI. Most preferred SCR catalyst materials comprise zeolites having a CHA structure type.

[0091] The zeolitic chabazite-containing SCR catalyst material preferably has the approximate formula (Ca, Na, K, Mg)AlSiO 126H2O (e.g., hydrated calcium aluminum silicate), is a naturally occurring tectosilicate mineral of the zeolite group. Three synthetic forms of zeolitic chabazite suitable for use in the SCR catalyst of the present invention are described in "Zeolite Molecular Sieves" by D.W. 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); Zeolite D of Barrer et al., described in British Patent No. 868,846 (1961); and Zeolite R, described in U.S. Pat. No. 3,030 to Milton, all of which are incorporated herein by reference. The synthesis of another synthetic form of zeolitic chabazite, SSZ-13, is described in U.S. Pat. No. 4,544,538 to Zornes, which is incorporated herein by reference. A method for making yet another synthetic molecular sieve having the chabazite structure, SAPO-44, is described in US Pat. No. 6,162,415 to Liu et al., which is incorporated herein by reference.

[0092] The silica-to-alumina ratio in molecular sieves useful as SCR catalyst materials in the present invention can vary over a wide range. Preferred molecular sieves useful as SCR catalyst materials have a silica-to-alumina molar ratio (SAR) in the range of 2 to 300, including 5 to 250, 5 to 200, 5 to 100, and 5 to 50. More preferably, the molecular sieves have a silica-to-alumina molar ratio (SAR) in the range 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 immediately preceding SAR ranges, the spherical particles of the molecular sieve have a particle size d in the range of about 1.0 to about 5 microns, more specifically about 1.0 to about 3.5 microns. 50The individual crystals of the molecular sieve component have a crystal size in the range of about 100 to about 250 nm.

[0093] Metal-promoted zeolite catalysts, particularly iron- and copper-promoted zeolite catalysts, are preferred for the selective catalytic reduction of nitrogen oxides, e.g., with ammonia. The promoter metal can be selected from Cu, Fe, Co, Ni, La, Ce, Mn, V, Ag, and combinations thereof. Preferred promoter metals are Cu, Fe, or combinations thereof. Thus, the preferred metal-promoted zeolites included in the selective catalytic reduction (SCR) catalyst of the present invention are either copper-promoted zeolites or iron-promoted zeolites, particularly copper-promoted chabazite zeolites or iron-promoted chabazite zeolites, or both.

[0094] Preferred SCR catalysts contain no 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 interest as catalysts for the selective catalytic reduction of nitrogen oxides in lean-burn engines using a nitrogenous reductant. The promoter metal content in such preferred catalysts, calculated as the 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 up to about 10 wt. %, or more preferably in the ranges of 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 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, can range from about 1 to about 4 wt. %.

[0095] One exemplary molecular sieve that may be useful as an SCR catalyst material is an aluminophosphate. Types of aluminophosphates include silicoaluminophosphate (SAPO), metalloaluminophosphate (MeAPO), and metallosilicoaluminophosphate (MeSAPO). The preparation of a synthetic form of an exemplary aluminophosphate molecular sieve, silicoaluminophosphate 34 (SAPO-34), is described in U.S. Patent No. 4,440,871 to Lok et al. and U.S. Patent No. 7,264,789 to Van Den et al., both of which are incorporated herein by reference. A method for making 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.

[0096] The SCR catalyst of the present invention preferably comprises a metal oxide, e.g., a mixed oxide. As used herein, the term "mixed oxide" refers to an oxide containing cations of two or more chemical elements or cations of a single element in several oxidation states. Mixed oxides suitable as SCR catalysts include Fe / titania (e.g., FeTiO), Fe / alumina (e.g., FeAlO), Mg / titania (e.g., MgTiO), Mg / alumina (e.g., MgAlO), Mn / alumina, Mn / titania (e.g., MnO), and the like. x / TiO2) (e.g., MnO x Examples of mixed oxides as SCR catalysts include Cu / Al2O3), Cu / titania (e.g., CuITiO3), Ce / Zr (e.g., CeZrO2), Ti / Zr (e.g., TiZrO2), and mixtures thereof. Further examples of mixed oxides as SCR catalysts are described in U.S. Patent Application Publication No. 2001 / 0049339 to Schafer-Sindelindger et al., U.S. Patent No. 4,518,710 to Brennan et al., U.S. Patent No. 5,137,855 to Hegedus et al., U.S. Patent No. 5,476,828 to Kapteijn et al., U.S. Patent No. 8,685,882 to Hong et al., and U.S. Patent No. 9,101,908 to Jurng et al., all of which are incorporated herein by reference in their entireties.

[0097] The SCR catalyst may include one or more vanadium-containing components. Such compositions are generally referred to herein as "vanadia-based compositions." In such embodiments, the vanadium may be in various forms, including, but not limited to, free vanadium, vanadium ions, or vanadium oxides (vanadia), such as vanadium pentoxide (VO). As used herein, "vanadia" or "vanadium oxide" is intended to encompass all oxides of vanadium, including vanadium pentoxide. The vanadia-based composition preferably comprises a mixed oxide containing vanadia. The amount of vanadia in the mixed oxide may vary and preferably ranges from about 1 to about 10 weight percent, based on the total weight of the mixed oxide. For example, the amount of vanadia can be at least 1 percent, at least 2 percent, at least 3 percent, at least 4 percent, at least 5 percent, or at least 6 percent, with an upper limit of about 10 percent by weight, or 10 percent or less, 9 percent or less, 8 percent or less, 7 percent or less, 6 percent or less, 5 percent or less, or 4 percent or less, and a lower limit of about 1 percent by weight.

[0098] Preferred SCR compositions comprise vanadium supported on a refractory solid oxide such as alumina, silica, zirconia, titania, ceria, and combinations thereof, and are described in U.S. Pat. No. 4,010,238 to Shiraishi et al., U.S. Pat. No. 4,085,193 to Nakajima et al., and U.S. Patent Application Publication No. 2017 / 0341026 to Chen et al., which are incorporated herein by reference in their entireties. In another preferred embodiment, the SCR catalyst comprises a mixed oxide comprising vanadia / titania (VO / TiO), e.g., in the form of titania with dispersed vanadia. The vanadia / titania may optionally be activated or stabilized with tungsten (e.g., WO) to provide VO / TiO / WO, e.g., in the form of titania with dispersed VO and WO. Vanadia is not always in the form of a true mixed metal oxide; rather, the metal oxide components (e.g., titania and vanadia) may be present as discrete particles. The amount of tungsten in such embodiments may vary, for example, from about 0.5 to about 10 weight percent, based on the total weight of the mixed oxide. For example, the amount of tungsten may be at least 0.5 percent, at least 1 percent, at least 2 percent, at least 3 percent, at least 4 percent, at least 5 percent, or at least 6 percent, with an upper limit of about 10 weight percent, or 10 percent or less, 9 percent or less, 8 percent or less, 7 percent or less, 6 percent or less, 5 percent or less, or 4 percent or less, and a lower limit of about 0.5 weight percent.

[0099] Exemplary vanadia-based SCR compositions can include components including, but 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. Pat. No. 4,782,039 to Lindsey, U.S. Pat. No. 8,975,206 to Schermanz et al., and WO 2010 / 121280 to Schermanz et al., which are incorporated herein by reference in their entireties.

[0100] Certain vanadia-based SCR catalyst compositions may contain other active components (e.g., other metal oxides). For example, in some embodiments, vanadia-based SCR compositions suitable for use in the disclosed systems contain vanadia and antimony. Such vanadia-based SCR compositions, in certain embodiments, include a composite oxide containing vanadium and antimony that may be supported on a refractory metal oxide (e.g., TiO, SiO, WO, AlO, ZrO, or a combination thereof). Exemplary vanadia-based SCR compositions containing vanadia and antimony are disclosed in U.S. Pat. No. 4,221,768 to Inoue et al., WO 2017 / 101449 to Zhao et al., and International Application Nos. PCT / CN2016 / 113637, filed December 30, 2016, PCT / CN2015 / 076895, filed April 17, 2015, and PCT / CN2015 / 097704, filed December 17, 2015, all of which are incorporated herein by reference in their entireties. In certain embodiments, the SCR catalyst can include a mixture of a vanadium-based SCR composition and a molecular sieve.

[0101] 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, suitable for converting excess ammonia in an exhaust system to nitrogen.

[0102] Ammonia oxidation (AMOx) generally refers to the process of reacting ammonia with oxygen to produce N. Ammonia oxidation catalysts AMOx are preferably capable of converting excess ammonia primarily to N while minimizing nitrogen oxide by-products, such as nitrogen oxides (NOx), over a wide range of temperatures where ammonia slip would otherwise escape during a vehicle's driving cycle. Thus, AMOx catalysts also produce minimal NO, an undesirable and potent greenhouse gas.

[0103] The composition of the AMOx catalyst is not particularly limited, and various compositions known to be suitable for this purpose can be used in the context of the disclosed exhaust gas treatment system. The ammonia oxidation catalyst component is generally preferably a composition, preferably a physical mixture, comprising one or more platinum group metals supported on a refractory metal oxide.

[0104] The AMOx catalyst preferably comprises at least one supported platinum group metal, which is effective for removing ammonia from exhaust gas streams. Preferred platinum group metals include ruthenium, rhodium, iridium, palladium, platinum, silver, or gold. The platinum group metal component can comprise physical mixtures and / or chemically and / or atomically doped combinations of ruthenium, rhodium, iridium, palladium, platinum, silver, and gold. In a highly preferred embodiment, the AMOx catalyst comprises a noble metal or platinum group metal (PGM), such as platinum, palladium, rhodium, or a combination thereof. It is particularly preferred that the AMOx catalyst comprise platinum. It is highly preferred that the at least one platinum group metal, most preferably platinum, and optionally platinum and rhodium, is present in an amount ranging from about 0.008 wt. % to about 2 wt. % (metal), based on the loading of the Pt-group metal support.

[0105] The AMOx catalyst function according to the present invention is about 0.1 g / ft, calculated as the total weight of precious metals or platinum group metals relative to the volume of the AMOx catalyst. 3 ~about 10g / ft 3 , preferably about 0.3 g / ft 3 ~about 5g / ft 3 , more preferably about 0.5 g / ft 3 ~About 3g / ft 3 , and even more preferably about 0.8 g / ft 3 ~about 2g / ft 3Alternatively or additionally, the AMOx compositions disclosed herein comprise a total precious metal or platinum group metal loading of about 0.01 wt. % to about 2 wt. %, preferably about 0.05 wt. % to about 1 wt. %, and more preferably about 0.08 wt. % to about 0.5 wt. %, based on the weight of the dry AMOx catalyst component.

[0106] Preferably, the precious metal or platinum group metal component of the ammonia oxidation catalyst component comprises, and preferably consists of, platinum (Pt). The ammonia oxidation catalyst has a metal content of about 0.5 g / ft 3 ~about 10g / ft 3 %, more preferably in the range of about 0.01 wt. % to about 2 wt. %, or at total platinum loadings and / or platinum amounts as defined above for common noble metals or platinum group metals.

[0107] Alternatively, the precious metal component or platinum group metal of the ammonia oxidation catalyst component comprises, and preferably consists of, palladium (Pd). The ammonia oxidation catalyst has a concentration of about 0.5 g / ft 3 ~about 10g / ft 3 %, more preferably in the range of about 0.01% to about 2% by weight, or the total palladium loading and / or palladium amount defined above for common noble metals or platinum group metals.

[0108] Alternatively, the precious metal component or platinum group metal of the ammonia oxidation catalyst component comprises, and preferably consists of, rhodium (Rh). The ammonia oxidation catalyst has a concentration of about 0.5 g / ft 3 ~about 10g / ft 3 % to about 2 wt. %, more preferably in the range of about 0.01 wt. % to about 2 wt. %, or at total rhodium loadings and / or rhodium amounts defined above for common noble metals or platinum group metals.

[0109] Those skilled in the art are familiar with determining the loading of precious metals or platinum group metals on catalytic coatings. For example, XRF (X-ray fluorescence) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) can be used to measure catalyst loading.

[0110] The noble metal or platinum group metal of the AMOX catalyst of the present invention is preferably supported on a high surface area refractory metal oxide support, for example. 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. Refractory metal oxides may include mixed oxides such as silica-alumina, amorphous or crystalline aluminosilicates, alumina-zirconia, alumina-lanthana, alumina-chromia, alumina-barria, and alumina-ceria. Exemplary refractory metal oxides have a high surface area, preferably from about 50 to about 300 m. 2 It contains γ-alumina with a specific surface area of ​​1 / g.

[0111] 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, 1-10% SiO-AlO), titania or doped titania materials, such as Si-doped titania materials (including, but not limited to, 1-15% SiO-TiO), or zirconia or doped zirconia materials, such as Si-doped ZrO (including, but not limited to, 5-30% SiO-ZrO).

[0112] High surface area metal oxide supports, such as alumina or titania support materials, typically have a surface area of ​​about 50 m 2 / g~about 400m 2 / g, preferably about 60m 2 / g ~ approx. 350m 2 / g, for example, about 90m 2 / g ~ approx. 250m 2 The total surface area (BET) is shown in g / g.

[0113] The refractory metal oxide support material is preferably from about 0.3 to about 1.5 cm 3 / g。 Activated alumina has a total pore volume BET in the range of about 2 to about 50 nm.

[0114] In one or more embodiments, the ammonia oxidation catalyst (AMOx) has a particle size distribution D 50 and / or the ammonia oxidation catalyst has a particle size distribution d 90 It has.

[0115] In one or more embodiments, the ammonia oxidation catalyst (AMOx) is present in an amount of from about 50 to about 700 m 2 In one or more embodiments, the ammonia oxidation catalyst has a surface area (BET) in the range of about 0.3 to about 1.5 cm / g. 3 In one or more embodiments, the ammonia oxidation catalyst has an average pore volume (BET) in the range of about 2 to about 50 nm. In one or more embodiments, the ammonia oxidation catalyst has an average pore size (BET) in the range of about 0.3 to about 3.0 g / in 3 The coating is then coated onto the substrate with a drying increase of 100%.

[0116] In a preferred embodiment, the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention includes an additional three-way catalyst (TWC). Those skilled in the art will be familiar with the general characteristics of three-way catalysts (TWCs) as described in the art. Also, three-way catalysts (TWCs) have been previously described with respect to TWCs in close-coupled positions at the outlet of a gasoline engine. Accordingly, these descriptions also apply to three-way catalysts (TWCs) added to the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention.

[0117] The most significant difference between the three-way catalyst (TWC) preferably included in the ammonia oxidation catalyst (AMOx) and the ammonia oxidation catalyst (AMOx) itself is that the three-way catalyst (TWC) includes an oxygen storage component (OSC). It is common knowledge that the presence of an oxygen storage component (OSC) in a three-way catalyst (TWC) is important for the coordinated removal of nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) from the exhaust gas stream of a gasoline engine. Therefore, a preferred three-way 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 previously described elsewhere herein, the preferred oxygen storage component (OSC) is a ceria-based material, i.e., a cerium oxide-based material that can be preferably used as a support material for at least one platinum group metal in the three-way catalyst (TWC) of the ammonia oxidation catalyst (AMOx) of the exhaust gas treatment system of the present invention. As already described in more detail herein, materials comprising ceria with one or more oxides of cerium or other oxides are particularly preferred. Highly preferred are mixed oxides (or mixtures) of ceria and zirconia.

[0118] In some embodiments, the ammonia oxidation catalyst (AMOx) of the inventive exhaust gas treatment system of the present invention may not include an additional oxygen storage component (OSC), thereby effectively not including a three-way catalyst (TWC), particularly in situations where the ammonia oxidation catalyst (AMOx) defined herein is combined with an additional selective catalytic reduction catalyst (SCR) in a single catalyst layer. Alternatively, the ammonia oxidation catalyst (AMOx) of the inventive exhaust gas treatment system may preferably include catalytic functions that constitute a three-way catalyst (TWC), particularly due to the presence of an oxygen storage component (OSC). The latter configuration is particularly preferred when the catalytic function for reducing ammonia tailpipe emissions includes a combination of at least a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx), and a zoned presentation of the latter two catalytic functions is selected. In this preferred configuration, the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx), along with the optional three-way catalyst (TWC), are separately disposed, preferably at the inlet and outlet, respectively, of the flow-through support material.

[0119] One advantage of a zoned configuration of the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx), preferably with an additional three-way conversion catalyst (TWC), is that the amount of selective catalytic reduction catalyst (SCR) and / or ammonia oxidation catalyst (AMOx), preferably with a three-way conversion catalyst (TWC), used 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 one single catalyst washcoat layer. Without being bound by theory, the inventors believe that the zoned presentation of the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) has the technical advantage that the latter two catalytic functions do not come into direct contact with each other, even over long-term operation of the corresponding exhaust gas treatment system during difficult real-life conditions, including long-term degradation of the entire system under high temperatures and harsh environmental conditions. Thus, by permanently separating the catalytic functions at different locations, the inventors believe that the selective catalytic reduction catalyst (SCR) and ammonia oxidation catalyst (AMOx) with the preferred three-way conversion catalyst (TWC) cannot directly interact with each other and / or potentially adversely affect the mutual stability of each catalytic function, thereby enabling better long-term stability and effectiveness of the overall catalytic function for reducing ammonia emissions at the tailpipe. Clearly, the additional option of limiting, or even substantially reducing, catalyst loading in more efficient, or at least equally efficient, exhaust gas treatment systems capable of meeting future emission regulations offers a high technical advantage.

[0120] When the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) are combined into a single layer on a substrate, it is preferred to prepare the single layer from a single combined slurry containing the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) containing a metal-promoted zeolite. However, the single combined slurry used to prepare the single layer containing the catalytic functionality for reducing ammonia tailpipe emissions is preferably obtained by blending a first slurry and a second slurry prepared separately. The first slurry is used to prepare the ammonia oxidation catalyst (AMOx) containing at least one catalytically active metal on an alumina support. The second slurry is used to prepare the selective catalytic reduction catalyst (SCR) containing a metal-promoted zeolite. The first and second slurries are blended into a single combined slurry containing at least the selective catalytic reduction catalyst (SCR) and the ammonia oxidation catalyst (AMOx) to obtain the single-slurry, single-layer design of the present invention according to this first alternative form of catalytic functionality for reducing ammonia tailpipe emissions in the exhaust gas treatment system of the present invention.

[0121] Thus, in one preferred alternative, a method of preparing an exhaust gas treatment system of the present invention includes the steps of providing a three-way catalyst (TWC) and a gasoline particulate filter (GPF), preferably a four-way 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) comprising a metal-promoted zeolite; blending the first and second slurries to remove the ammonia oxidation catalyst (AMOx) from the first slurry and the selective catalytic reduction catalyst (SCR) from the second slurry; obtaining a single combined slurry comprising the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR); impregnating a carrier with the single combined slurry to obtain a catalytic function for reducing tailpipe emissions of ammonia comprising the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR) combined in a single layer on the carrier; and disposing the catalytic function for reducing tailpipe emissions of ammonia comprising the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR) downstream of a three-way catalyst (TWC) and a gasoline particulate filter (GPF), preferably a four-way catalyst (FWC).

[0122] At least one catalytically active metal, preferably platinum and / or rhodium, or palladium and / or rhodium, or a combination of platinum, palladium, and rhodium impregnated on an alumina support, preferably zirconia-doped alumina, is preferably thermally set to obtain a first slurry. The solids content of the first slurry is preferably in the range of 50 to 85 wt. %, more preferably 60 to 80 wt. %, and even more preferably 70 to 75 wt. Alternatively, the at least one catalytically active metal on the alumina support may contain no rhodium at all, or may contain platinum and / or palladium in combination with at least one non-platinum group metal, such as titanium and / or manganese, to replace the rhodium, and may typically be impregnated onto the alumina support by thermal setting. The solids content of the first slurry is preferably in the range of 50 to 85 wt. %, more preferably 55 to 75 wt. %, and even more preferably 60 to 70 wt. %.

[0123] Particle size distribution D of a first slurry containing an ammonia oxidation catalyst (AMOx) comprising at least one catalytically active metal on an alumina support 90 is preferably 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.

[0124] In this method, the particle size distribution D of the single combined slurry used to obtain catalytic functionality for reducing tailpipe emissions of ammonia, comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support, is 90 It is further preferable that the thickness is in the range of 2 to 50 microns, preferably 5 to 30 microns, more preferably 8 to 25 microns, and most preferably 10 to 17 microns.

[0125] In a preferred embodiment, the second slurry containing the selective catalytic reduction catalyst (SCR) can already contain a metal-promoted zeolite containing catalytic functionality. That is, the metal-promoted zeolite is formed separately, for example, by metal exchange or metal promotion of a metal-free zeolite, and then the second slurry is formed by providing the metal-promoted zeolite in the second slurry. In this preferred embodiment, the metal-promoted zeolite, such as a copper- or iron-promoted zeolite, more preferably a copper- or iron-promoted chabazite zeolite, is added to the second slurry before the second slurry is blended with the first slurry containing an ammonia oxidation catalyst (AMOx) containing at least one catalytically active metal on an alumina support. The particle size distribution D of the second slurry containing the selective catalytic reduction catalyst (SCR) can be calculated as follows: 90Preferably, the particle size is in the range of 0.5 to 25 microns, preferably 1 to 20 microns, more preferably 2 to 15 microns, and most preferably 3 to 8 microns. Optionally, zirconia can be added to the second slurry, preferably at a solids content of 25 to 60 wt %, more preferably 30 to 50 wt %, or most preferably 35 to 45 wt %. The combined slurry used to prepare a catalytic function for reducing ammonia tailpipe emissions, including an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in one single layer, is then formed by impregnating the combined slurry onto a support.

[0126] In another preferred alternative embodiment of the method for preparing an exhaust gas treatment system of the present invention, a combined slurry containing the ammonia oxidation catalyst (AMOx) from the first slurry and the selective catalytic reduction catalyst (SCR) from the second slurry is obtained by using the second slurry, and the metal-promoted zeolite of the selective catalytic reduction catalyst (SCR) is prepared by a slurry-metal ion exchange process in the second slurry, the process comprising the steps of providing a slurry containing 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 containing the selective catalytic reduction catalyst (SCR) containing the metal-promoted zeolite. The particle size distribution D in the second slurry containing the selective catalytic reduction catalyst (SCR) containing the metal-promoted zeolite is 90 is preferably in the range of 0.5 to 25 microns, preferably 1 to 20 microns, more preferably 2 to 15 microns, and most preferably 3 to 8 microns. Optionally, zirconia can be added to the second slurry, preferably at a solids content of 25 to 60 wt %, more preferably 30 to 50 wt %, or most preferably 35 to 45 wt %. In this preferred alternative, the particle size distribution D of the single combined slurry used to provide catalytic functionality for reducing ammonia tailpipe emissions, comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support, is 90It is further preferable that the thickness is in the range of 2 to 50 microns, preferably 5 to 30 microns, more preferably 8 to 25 microns, and most preferably 10 to 17 microns.

[0127] The final single layer washcoat resulting from impregnation of the combined slurry, after optional coating, drying (e.g., at 120-180°C) and calcination (e.g., at 400-600°C) to obtain catalytic functionality for reducing tailpipe ammonia emissions, preferably has a coating weight of 0.2-35 g / in. 3 , more preferably 0.5 to 15 g / in 3 , and even more preferably 0.8 to 5 g / in 3 , e.g., 1.0 to 3.5 g / in 3 , or most preferably 1.5 to 2.5 g / in 3 The total amount is

[0128] The loading of platinum group metal on the support in the single layer approach is generally between 0.2 and 28 g / ft of the volume of the AMOx catalyst. 3 , more preferably 0.5 to 17 g / ft 3 , and even more preferably 1 to 8 g / ft 3 , most preferably 2 to 5 g / ft 3 is.

[0129] The catalytic function for reducing ammonia tailpipe emissions, including an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a carrier, is coated on a suitable substrate, preferably a typical flow-through substrate. The substrate may typically be a monolith. The substrate preferably has a honeycomb structure. Particularly preferred is a ceramic honeycomb substrate.

[0130] According to a second alternative, the combination of a selective catalytic reduction catalyst (SCR) and an ammonia oxidation catalyst (AMOx) can be presented as a zoned catalytic function, where 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 arranged in separate locations on a suitable carrier or support, with the different zones for the various catalytic functions being arranged axially along the catalyst and substrate and / or the exhaust gas flow from the gasoline engine.

[0131] Preferably, a selective catalytic reduction catalyst (SCR) comprising a metal-promoted zeolite is washcoated in the inlet zone of the catalytic function for reducing ammonia emissions from the tailpipe, and an ammonia oxidation catalyst (AMOx), preferably comprising an additional three-way conversion (TWC) catalytic function, is washcoated in the outlet zone of the catalytic function for reducing ammonia emissions from the tailpipe.

[0132] For the inlet zone, i.e., the first zone, the 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 selective catalytic reduction catalyst (SCR) and ammonia oxidation catalyst (AMOx).

[0133] However, it is preferred to use a selective catalytic reduction catalyst (SCR) comprising a metal-supported zeolite in a lesser amount in a zoned approach when compared to the alternative single layer approach.

[0134] The inlet zone of the substrate in the zoned approach can be coated with the SCR catalyst comprising the metal-supported zeolite according to established washcoating procedures familiar to those skilled in the art. One preferred option is to prepare a catalyst washcoat comprising the SCR catalyst comprising the metal-supported zeolite according to the descriptions provided elsewhere herein for the composition and preparation of the SCR catalyst comprising the metal-supported zeolite present in the single layer approach.

[0135] For the outlet zone, i.e., the second zone, a three-way catalyst (TWC) preferably comprising at least one platinum group metal, an oxygen storage component (OSC) preferably comprising ceria-zirconia, and optionally an ammonia oxidation catalyst (AMOx) comprising a promoter preferably comprising a barrier are coated to form a catalytic function for reducing tailpipe emissions of ammonia.

[0136] The exit zone of the substrate in a zoned approach can be coated with an ammonia oxidation catalyst (AMOx), preferably containing an additional three-way catalyst (TWC), according to established washcoating procedures familiar to those skilled in the art.

[0137] One preferred option is to prepare a catalyst washcoat comprising an ammonia oxidation catalyst (AMOx) with an additional three-way catalyst (TWC), preferably in accordance with the description given elsewhere herein for the composition and preparation of an ammonia oxidation catalyst (AMOx) with an additional three-way catalyst (TWC), in a single layer approach.

[0138] For example, an ammonia oxidation catalyst (AMOx), preferably containing an additional three-way catalyst (TWC), can contain at least one catalytically active metal, preferably platinum and / or rhodium, or palladium and / or rhodium, or even a combination of platinum and palladium with 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 used to prepare an AMOx containing at least one catalytically active metal and a support material may not thermally fix at least one platinum group metal on the support. The resulting washcoat containing the slurry and AMOx preferably also contains a typical promoter, preferably a barrier, for better stability. The particle size distribution D in a slurry containing an ammonia oxidation catalyst (AMOx) containing an additional three-way catalyst (TWC) is: 90is preferably 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.

[0139] In the present invention, the particle size distribution D of the single combined slurry used to obtain catalytic function for reducing tailpipe emissions of ammonia, comprising an ammonia oxidation catalyst (AMOx) and a selective catalytic reduction catalyst (SCR) combined in a single layer on a support, is 90 It is further preferable that the thickness is in the range of 2 to 50 microns, preferably 5 to 30 microns, more preferably 8 to 25 microns, and most preferably 10 to 17 microns.

[0140] The loading of platinum group metal on the support in the zoned approach is generally between 0.2 and 28 g / ft of the volume of the AMOx catalyst. 3 , more preferably 0.5 to 17 g / ft 3 , and even more preferably 1 to 8 g / ft 3 , most preferably 2 to 5 g / ft 3 is.

[0141] In a zoned configuration, the total amount of washcoat is preferably 0.2 to 35 g / in 3 , more preferably 0.5 to 15 g / in 3 , and even more preferably 0.8 to 5 g / in 3 , e.g., 1.0 to 3.5 g / in 3 , or most preferably 1.5 to 2.5 g / in 3 is the amount.

[0142] The present invention is also directed to a method of treating an exhaust gas stream from a gasoline engine, the method comprising the steps of providing an exhaust gas stream from the gasoline engine containing ammonia, and contacting the exhaust gas stream containing ammonia with an exhaust gas treatment system according to the present invention to reduce ammonia emissions in the exhaust gas stream at a tailpipe. [Example]

[0143] Catalyst preparation test description Three-way catalyst (TWC): 80g / ft 3 PtPdRh 0 / 72 / 8 This technology involves Pd impregnated onto highly porous alumina in a single layer design. The main components of the slurry are highly porous alumina and ceria-zirconia, the latter of which is impregnated with Pd, while the former is loaded with Rh using aqueous solutions of palladium nitrate and rhodium nitrate, respectively. The final dry Pd content is 72 g / ft 3 The Rh content after drying is 8g / ft 3 In both cases (Pd or Rh), the process involves Pd or Rh impregnation on a selected support, followed by heat setting of the PGM-containing frit (60-75% solids) at 400-600°C for 2-4 hours.

[0144] Slurries were prepared from the calcined PGM-containing frits using distilled water and surfactants such as n-octanol under constant stirring. Zirconia and / or barrier were added during slurry preparation using appropriate precursors, ranging from 1 to 4 wt% for zirconia and 1 to 10 wt% for barrier, based on the total solids. The solids content of the slurry was adjusted (35 to 45%) for pH and viscosity measurements and to enhance wet milling. After milling, the pH was adjusted (3.5 to 4.5) with nitric acid. The particle size distribution (Deo) of the slurry was also measured after milling and ranged from 13 to 19 μm.

[0145] Ceramic honeycomb flow-through substrates (4.66 x 4.5", 600 / 4) were coated, dried (120-180°C), and fired in air (400-600°C). The total washcoat loading was 2.8-3.5 g / in 3 is.

[0146] Four-way conversion catalyst (FWC): 10g / ft 3 PtPdRh 0 / 8 / 2 This formulation contains Pd impregnated onto high-porosity alumina using a single slurry with a washcoat loading of 1.5 g / in. The main components of the slurry are high-porosity alumina and ceria-zirconia, the latter impregnated with Pd, while the former is supported with Rh using aqueous solutions of palladium nitrate and rhodium nitrate, respectively. The final dried Pd content is 8 g / ft®, and the dried Rh content is 2 g / ft®. In both cases (Pd or Rh), the process involves Pd or Rh impregnation on the selected support, followed by heat setting of the PGM-containing frit (60-75% solids) at 400-600°C for 2-4 hours.

[0147] The calcined PGM-containing frit was slurried with distilled water and a surfactant, such as n-octanol, under constant stirring. Zirconia and / or barrier were added during slurry preparation using appropriate precursors, ranging from 1 to 4 wt% for zirconia and 1 to 5 wt% for barrier, respectively. The solids content of the slurry was adjusted (35-42%) to enhance pH and viscosity measurements and wet milling. After milling, the pH was adjusted (3.2-4.0) with nitric acid. The particle size distribution (D90) of the slurry was also measured before and after slurry milling (10-15 μm) at the required solids content.

[0148] A ceramic honeycomb wall flow substrate (4.66 x 4", 300 / 8) was coated, dried (120-180°C), and fired in air (400-600°C).

[0149] Reference system (TWCUF): 4g / ft 3 0 / 3 / 1 Pt / Pd / Rh This technology contains Pd and Rh on highly porous alumina and ceria-zirconia supports and barriers. This technology is a low-washcoat three-way catalyst for underfloor applications for HC, CO, and NOx purification. The main components of the slurry are highly porous alumina and ceria-zirconia, the latter impregnated with Pd, while the former is supported with Rh using aqueous solutions of palladium nitrate and rhodium nitrate, respectively. The final dry Pd content is 3 g / ft³, and the dry Rh content is 1 g / ft³. This slurry preparation involves wet impregnation of the precious metals onto the selected support, followed by wet milling after appropriate pH adjustment. The solids content of the slurry was adjusted (35-45%) to enhance pH and viscosity measurement and wet milling. After milling, the pH was adjusted (3.5-5.0) with nitric acid. The slurry particle size distribution (D90) was also measured after milling and was in the range of 12-22 μm.

[0150] Ceramic honeycomb flow-through substrates (5.66 x 3", 400 / 3) were coated, dried (120-180°C), and fired in air (400-600°C). The total washcoat amount ranged from 1.5 to 2.5 g / in3.

[0151] Example 1 of the present invention (SCR / AMOx): 4 g / ft 3 3 / 0 / 2 Pt / Pd / Rh This catalyst is a single-slurry, single-layer design that combines PGM and zeolite in one slurry. Pt and Rh are sequentially impregnated into zirconia-doped, high-porosity alumina at high solids, followed by heat setting. The slurry solids are in the 70-75% range. The first slurry preparation step is completed by wet-milling to a D90 range of 12-22 microns. The next step involves a separate slurry preparation with Cu-chabazite zeolite by stirring the zeolite in distilled water and adding zirconia at a solids range of 35-45%. The zeolite slurry is dispersed to a D90 range of 3-8 microns by low-energy mixing. The final slurry process involves blending the PGM-containing slurry with the zeolite slurry, followed by thorough mixing. The particle size distribution (D90) of the final slurry is in the 10-17 micron range.

[0152] Ceramic honeycomb flow-through substrates (5.66 x 3", 400 / 3) were coated, dried (120-180°C), and fired in air (400-600°C). The total washcoat amount ranged from 2.5 to 3.5 g / in3.

[0153] Example 2 of the present invention (SCR / AMOx): 4 g / ft 3 4 / 0 / 0 Pt / Pd / Rh This catalyst is also a single slurry monolayer design combining PGM and zeolite in one slurry. The difference from Inventive Example 1 is that Rh is now replaced by Ti and Mn, which are sequentially impregnated after Pt on high porosity alumina from their respective precursors at high solids content of 60-70%, followed by heat setting. The calcined powder is stirred in distilled water at the appropriate pH and then quenched. 90The zeolite is slurried by wet milling to a PSD in the range of 12-22 microns, completing the first slurry preparation step. The next step involves a separate slurry preparation with Cu-chabazite zeolite by stirring the zeolite in distilled water and adding zirconia at a solids content in the range of 35-45%. The zeolite slurry process differs from that of Example 1 in that Cu exchange is performed during a slurry process called ISIE (In Slurry Ion Exchange). The zeolite slurry is then mixed with low-energy mixing to produce a D in the range of 3-8 microns. 90 The final slurry process involves blending the PGM-containing slurry with the zeolite slurry, followed by thorough mixing. The particle size distribution (D 90 ) ranges from 10 to 17 microns.

[0154] Ceramic honeycomb flow-through substrates (5.66 x 3", 400 / 3) were coated, dried (120-180°C), and fired in air (400-600°C). Total washcoat mass is 1.0 to 1.5 g / in3.

[0155] Example 3 of the present invention (SCR / TWC-AMOx): 3 g / ft 3 2 / 0 / 1 Pt / Pd / Rh This formulation was designed using a washcoat zoning concept, where the axial length of the catalyst is divided into two zones (inlet / outlet) to accommodate washcoats with different compositions and functions in specific zones along the axial length. The inlet zone contains Cu-chabazite zeolite prepared similarly to the zeolite slurry of Inventive Example 1. However, the amount of zeolite used is less than Inventive Example 1 (half of the total zeolite in Inventive Example 1).

[0156] Cu-chabazite slurry preparation (inlet SCR zone) is carried out by stirring Cu-chabazite in distilled water with added zirconia at solids content ranging from 35 to 45%, followed by dispersive mixing.

[0157] The outlet zone contains Pt and Rh on high-porosity alumina and ceria-zirconia supports. The latter component provides oxygen storage capacity and enhances the functionality of the three-way catalyst. The slurry also contains barium oxide from a preferred precursor. Pt (50%) is impregnated into ceria-zirconia, and PtRh is impregnated into lanthanum-doped high-porosity alumina. This slurry does not involve thermal fixation of the PGMs and is primarily enhanced by a zoned washcoat concept, which mitigates negative zeolite / PGM interactions. Separate PGM frits are blended and diluted in distilled water at the appropriate pH and solids content, followed by a 15-25 micron D. 90 Wet milling into a range of PSD.

[0158] Ceramic honeycomb flow-through substrates (4.66 x 3", 400 / 3) were coated using Cu-zeolite slurry (50% inlet) and PGM-containing slurry (50% outlet), which were then dried in air (120-180°C) and calcined (400-600°C), respectively. The total washcoat amount was 2.5-3.5 g / in. 3 is.

[0159] Catalyst performance evaluation The catalysts were washcoated onto suitable substrates as described above. A close-coupled can (CC) is one in which a three-way catalyst (TWC) coated on a flow-through substrate and a four-way catalyst (FWC) coated on a wall-flow substrate are placed in the same can, with the TWC closer to the engine. The cans are used upstream for different downstream components (see system layout).

[0160] The evaluated components were aged in an oven unit equipped with gas dosing capability, as well as flow meters and thermocouples in the inlet and inner sections, respectively. The gas composition in the oven was 5% oxygen and 10% water (rest N2) for 15 hours at an inner oven temperature of 820 °C. All the different components were placed in the same oven and exposed to the same air mass flow at the same temperature.

[0161] The system and resulting component evaluation (WLTC) was carried out on a Euro 6 GTDI vehicle using a chassis dyno test cell, the latter fitted with thermal elements and FT-IR units at the engine outlet / catalyst inlet, catalyst bed and outlet positions, allowing for precise recording of temperatures and gaseous emissions along the exhaust line.

Claims

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

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

3. 3. The exhaust gas treatment system of claim 1 or 2, wherein the three-way catalyst and the gasoline particulate filter (GPF) are positioned upstream of the exhaust gas treatment system in a close coupled (CC) position relative to the gasoline engine.

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

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

7. The exhaust gas treatment system of any one of claims 1 to 5, wherein the ammonia oxidation catalyst (AMOx) is rhodium-free.

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

9. An exhaust gas treatment system according to any one of 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 zeolite.

10. 10. An exhaust gas treatment system according to any one of claims 1 to 9, wherein the catalytic function 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 catalyst (TWC) comprising at least one platinum group metal, an oxygen storage component (OSC) preferably comprising ceria-zirconia, and optionally a promoter, preferably comprising a barrier.

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

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

13. A method for preparing an exhaust gas treatment system according to any one of claims 5 to 13, comprising the steps of: - providing a three-way 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) comprising 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 catalytic functionality for reducing tailpipe ammonia emissions, comprising the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR) combined in a single layer on the support; - disposing the catalytic function for reducing the tailpipe ammonia emissions, including the ammonia oxidation catalyst (AMOx) and the selective catalytic reduction catalyst (SCR), downstream of the three-way catalyst (TWC) and the gasoline particulate filter (GPF).

14. 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) comprising the metal-promoted zeolite.

15. 14. A method of treating an exhaust gas stream from a gasoline engine, the method comprising the steps of providing an exhaust gas stream from the gasoline engine containing ammonia, and contacting the exhaust gas stream containing ammonia with an exhaust gas treatment system according to any one of claims 1 to 13 to reduce the ammonia emissions in the exhaust gas stream at the tailpipe.

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