Exhaust aftertreatment system for an internal combustion engine

Abstract

Exhaust aftertreatment device (24) for an internal combustion engine (12) of a motor vehicle, comprising at least one first catalyst (32) through which exhaust gas from the internal combustion engine (12) flows, comprising at least one particulate filter (30) through which exhaust gas flows and which is arranged downstream of the first catalyst (32) for retaining soot particles from the exhaust gas, and a second catalyst (28) through which exhaust gas flows, which is arranged downstream of the particulate filter (30) and is designed as an SCR catalyst, characterized in that the first catalyst (32) is a combination catalyst, with - a first catalyst part (40) which is designed as an SCR catalyst; - a second catalyst part (42) arranged downstream of the first catalyst part (40), which is designed as an ammonia slip catalyst and has a precious metal layer (44) with a first precious metal content; - a third catalyst part (46) arranged downstream of the second catalyst part (42), which is designed as an oxidation catalyst and has a precious metal layer (48) with a second precious metal content; and - an SCR layer (50) which is arranged on the precious metal layers (44, 48) of the second and third catalyst part (42, 46) and extends over the entire length (L) of the second and third catalyst part (42, 46).

Description

[0001] The invention relates to an exhaust aftertreatment device for an internal combustion engine, in particular of a motor vehicle, according to the preamble of claim 1.

[0002] Exhaust aftertreatment systems for internal combustion engines, especially those of motor vehicles, are already well known from the general state of the art and especially from series vehicle production.

[0003] The internal combustion engine has at least one combustion chamber, in particular in the form of a cylinder, into which fuel, in particular liquid fuel, and air are supplied during firing operation. This creates a fuel-air mixture in the combustion chamber, which is also referred to as the mixture and is burned. This results in exhaust gas from the internal combustion engine, which can flow out of at least one outlet of the internal combustion engine and thus out of the internal combustion engine itself.

[0004] For example, exhaust gas is routed to the exhaust aftertreatment system via exhaust piping, allowing the exhaust gas from the internal combustion engine to be treated. This system includes at least one SCR catalyst through which exhaust gas from the internal combustion engine flows, and which performs or supports selective catalytic reduction (SCR). This means that the SCR catalyst catalyzes the SCR reaction. Through selective catalytic reduction, nitrogen oxides (NOx) contained in the exhaust gas are reduced. xThe SCR process reduces nitrogen oxides, meaning they are at least partially removed from the exhaust gas. This removal of nitrogen oxides from the exhaust gas is also known as denitrification. During SCR, nitrogen oxides contained in the exhaust gas react, in particular, with components of a reducing agent introduced into the exhaust gas or with components that form from the reducing agent, to produce nitrogen and water. The reducing agent is typically an aqueous urea solution. During the SCR reaction, this aqueous urea solution produces effective ammonia (NH3) as nitrogen oxides are reduced.

[0005] Furthermore, exhaust aftertreatment systems for internal combustion engines, particularly those designed as diesel engines, include at least one particulate filter through which the exhaust gas flows and which is arranged upstream of the SCR catalyst in the direction of exhaust gas flow through the aftertreatment system, for retaining soot particles from the exhaust gas. The particulate filter filters the exhaust gas so that at least a portion of the soot particles contained in the exhaust gas is filtered out by the particulate filter. If the internal combustion engine is a diesel engine, the particulate filter is usually also referred to as a diesel particulate filter (DPF).

[0006] Furthermore, modern exhaust aftertreatment systems, especially those for diesel engines, typically feature an oxidation catalyst (DOC) in the direction of exhaust gas flow through the exhaust aftertreatment system upstream of the particulate filter.

[0007] From DE 10 2012 005 508 A1 a catalyst component of a motor vehicle exhaust gas purification system can be derived, which has a carrier body in honeycomb structure, on the channel walls of which an oxidation-catalytically effective coating with a precious metal content determined by at least one element of the platinum group and free of rhodium is applied continuously.The component has a first coating zone extending longitudinally from the inlet-side end to a first coating boundary and possessing a first precious metal content, furthermore a second coating zone extending longitudinally from the first coating boundary to a second coating boundary located behind the first coating boundary and possessing a second precious metal content that is reduced compared to the first precious metal content, and furthermore a third coating zone extending from the second coating boundary to the outlet-side end and possessing a third precious metal content that is reduced compared to the second precious metal content.

[0008] Furthermore, DE 10 2012 018 953 A1 discloses a method for operating an internal combustion engine in which, to support the regeneration of a particulate filter located in the exhaust system of the internal combustion engine and downstream of an oxidation catalyst, post-injections of fuel are carried out into at least one cylinder of the internal combustion engine by means of an injection valve. This involves advancing the closing point of an exhaust valve of a cylinder of the internal combustion engine in a first temperature range corresponding to a temperature of the oxidation catalyst. The post-injections take place in a second temperature range corresponding to the temperature of the oxidation catalyst, wherein the upper limit of the first temperature range is lower than the upper limit of the second temperature range.

[0009] Furthermore, DE 10 2006 038 291 A1 discloses an exhaust aftertreatment system for reducing nitrogen oxides and particulate matter in internal combustion engines operated with excess air, wherein nitrogen oxide reduction is achieved by means of an SCR catalyst and particulate matter reduction by means of a particulate separator or a particulate filter. An oxidation catalyst is arranged in the exhaust stream of the internal combustion engine, which converts at least some of the nitrogen monoxide contained in the exhaust stream into nitrogen dioxide. Downstream of the oxidation catalyst, a first particulate separator or particulate filter is arranged in the exhaust stream, which converts the soot particles deposited in the first particulate separator or particulate filter into carbon monoxide, carbon dioxide, nitrogen, and nitrogen monoxide using the nitrogen dioxide contained in the exhaust stream. Upstream of the first particulate separator or particulate filter, a partial exhaust stream branches off from the exhaust stream.Furthermore, storage tanks for a reducing agent and a metering device for the reducing agent are provided in the exhaust gas partial stream. This reducing agent is formed from a substance that releases ammonia downstream of the feed point through the hot exhaust gas, or from ammonia itself. Additionally, a second particulate separator or particulate filter is arranged downstream of the feed point in the exhaust gas partial stream. This filter is fed back into the exhaust gas stream downstream of the second particulate separator or particulate filter and downstream of the first particulate separator or particulate filter. Finally, an SCR catalyst is arranged downstream of the return point. This catalyst reduces the nitrogen oxides contained in the exhaust gas stream to nitrogen and water vapor using the released ammonia via selective catalytic reduction.

[0010] Furthermore, US patent 2011 / 0271664A1 describes a catalyst for treating an exhaust gas stream containing particulate matter, hydrocarbons, carbon monoxide, and ammonia. The catalyst has an inlet and an outlet end, which define an axial length, and a first catalytic coating containing a platinum group metal that extends over less than the entire axial length of the ends. It also has a second catalytic coating for selective catalytic reduction (SCR) of nitrogen oxides, which likewise extends over less than the entire axial length and overlaps the first coating in a portion.

[0011] The object of the present invention is to further develop an exhaust aftertreatment device of the type mentioned above in such a way that particularly emission-friendly operation can be achieved.

[0012] This problem is solved by an exhaust aftertreatment device with the features of claim 1. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0013] To further develop an exhaust aftertreatment device of the type specified in the preamble of claim 1 in such a way as to enable particularly low-emission operation, the invention provides that the exhaust aftertreatment device has a combination catalyst through which the exhaust gas flows and which is arranged upstream of the particulate filter. The combination catalyst comprises a first catalyst part, which is designed as an SCR catalyst or SCR catalyst part. This means that the first catalyst part effects or supports selective catalytic reduction (SCR), whereby nitrogen oxides (NOx) contained in the exhaust gas are reduced during the SCR reaction. xThe SCR process reduces nitrogen oxides, meaning they are at least partially removed from the exhaust gas. During the SCR reaction, nitrogen oxides contained in the exhaust gas react, in particular, with components of a reducing agent introduced into the exhaust gas or with components formed from the reducing agent, to produce nitrogen and water. The first catalyst component catalyzes the SCR reaction and thus exhibits an SCR effect, enabling the conversion of nitrogen monoxide (NO) and / or nitrogen dioxide (NO2) to nitrogen (N2).

[0014] The combination catalyst further comprises a second catalyst section, which is arranged downstream of the first catalyst section in the direction of exhaust gas flow through the exhaust aftertreatment system. This means that the exhaust gas flowing through the aftertreatment system first passes through the first catalyst section and then through the second. The second catalyst section is designed as an ammonia slip catalyst (ASC) and features a precious metal layer with a high initial precious metal content. In the ammonia slip catalyst, ammonia slip from the reducing agent is oxidized to nitrogen and water. The ASC effect refers to the catalytic action of the ammonia slip catalyst on the oxidation of ammonia (NH3).

[0015] The combination catalyst further comprises a third catalyst section, which is arranged downstream of the second catalyst section. Thus, the exhaust gas flowing through the exhaust aftertreatment system first passes through the first catalyst section, then through the second, and then through the third catalyst section, so that the exhaust gas flows through the first, second, and third catalyst sections sequentially. The third catalyst section is designed as an oxidation catalyst and has a precious metal layer containing a second precious metal. The oxidation catalyst, and thus the third catalyst section, has the function of oxidizing any carbon monoxide (CO) and any hydrocarbons (HC) that may be present in the exhaust gas.Thus, the third catalyst component catalyzes, that is, causes or supports, the oxidation of unburned hydrocarbons and carbon monoxide, so that the third catalyst component exhibits an OC effect, in particular a DOC effect. Furthermore, the combination catalyst has an SCR layer arranged on the noble metal layers of the second and third catalyst components, in particular an upper layer, which is formed, for example, as a copper-zeolite layer (Cu-Z layer) and extends over the entire length L of the second and third catalyst components.

[0016] The SCR layer is, for example, a fourth part of the combination catalyst, wherein the SCR layer is arranged or applied to the noble metal layers extending into deeper wall layers, so that the exhaust gas exiting the first catalyst part and flowing into the second catalyst part first encounters the SCR layer and then diffuses to the deeper noble metal layer of the second catalyst part. The SCR layer is understood to have an SCR effect, in which reduction reactions of nitrogen oxides with ammonia to nitrogen and water vapor are catalyzed. In the second and third catalyst parts of the combination catalyst according to the invention, the SCR layer is designed to reduce NH3 slip from the first catalyst part by means of SCR reactions.The SCR layer is advantageously arranged directly on the precious metal layers and thus comes into contact with them. The combination catalyst is particularly advantageous in such a way that the precious metal layers and the SCR layer of the second and third catalyst sections are applied to common catalyst base elements, and the second and third catalyst sections are directly adjacent to each other in the direction of exhaust gas flow and may even be in contact with each other. This allows the second and third catalyst sections to be designed to be particularly compact and manufactured at a particularly low cost.

[0017] By means of the exhaust gas aftertreatment device according to the invention, excessive nitrogen oxide emissions (NOx) can be reduced. x-Emissions), especially after a start, particularly a cold start, of the internal combustion engine and after the internal combustion engine has been operating in a low load range.The invention is based in particular on the realization that after a start, especially after a cold start, of the internal combustion engine, as well as after vehicle operation in the low-load range, especially after idling operation, i.e. also after coasting operation in which the internal combustion engine is in its idling mode, as well as after waiting times at traffic lights during which the internal combustion engine is running and in its idling mode, high nitrogen oxide emissions can typically occur, since in these vehicle operating conditions the catalysts and filters of the exhaust aftertreatment system cool down and are so cold after these vehicle operating conditions that in the subsequent starting or acceleration processes, in which very high exhaust emissions can occur, the catalysts and filters must first be brought back up to operating temperature.The exhaust aftertreatment device according to the invention is particularly advantageous for diesel motor vehicles and especially for diesel trucks, whose emissions, in particular nitrogen oxide emissions, can be kept particularly low by means of the exhaust aftertreatment device according to the invention.

[0018] The invention is further based, in particular, on the understanding that future emission requirements for internal combustion engines, especially diesel engines, increasingly focus on considering various secondary emissions such as NO2 and N2O, as well as the functionality of the exhaust aftertreatment system under real driving conditions. Conventional exhaust aftertreatment systems, which include an oxidation catalyst, a particulate filter located downstream of the oxidation catalyst, an SCR catalyst located downstream of the particulate filter, and an ASC (ammonia slip catalyst) located downstream of the SCR catalyst, prevent rapid heating of the SCR catalyst, especially after a cold start, and thus hinder high SCR catalyst efficiency.Advantageously, the first catalyst section of the combined catalyst of the exhaust aftertreatment system according to the invention, designed as an SCR catalyst, is the first exhaust aftertreatment device in the direction of flow after the exhaust gas exits the internal combustion engine, so that the exhaust gas temperatures in the first catalyst section of the exhaust aftertreatment system according to the invention are comparatively high. This allows the first catalyst section, designed as an SCR catalyst, to heat up relatively quickly after a start or low-load operation of the internal combustion engine, so that a higher NOx reduction efficiency can be achieved relatively quickly in the first catalyst section designed as an SCR catalyst. Hereinafter, the SCR catalyst of the first catalyst section of the exhaust aftertreatment system according to the invention will be referred to as the first SCR catalyst.

[0019] Cooling of catalysts and filters after a cold start or low-load operating conditions of the internal combustion engine is particularly pronounced in commercial vehicles or trucks, resulting in correspondingly higher exhaust emissions than in passenger cars. This is because, due to space constraints, commercial vehicles and trucks have a comparatively large distance and a correspondingly longer path between the internal combustion engine and the exhaust aftertreatment system compared to passenger cars, resulting in higher thermal losses in commercial vehicles and trucks than in passenger cars.In a conventional exhaust aftertreatment system, the injection of reducing agent into the exhaust gas is deactivated under the aforementioned operating conditions, i.e., during and for the warm-up phase after a start, especially a cold start, and during and for the warm-up phase after low-load operation, because the exhaust gas temperature is very low under these conditions. The injection of the reducing agent is deactivated to prevent crystallization. The injection of the reducing agent is typically only activated when an SCR catalyst, in which the reducing agent is to be converted, reaches a temperature greater than 180 degrees Celsius. Deactivating the injection of the reducing agent during the aforementioned operating conditions results in high nitrogen oxide emissions if no appropriate countermeasures are taken.

[0020] The exhaust aftertreatment system according to the invention enables extremely good cold-start performance and advantageous behavior under real driving conditions. Particularly in urban driving, NO2 secondary emissions can be kept especially low, particularly with NO2 concentrations of 50 percent or less. It has proven particularly advantageous if the first SCR catalyst is designed as a vanadium-based SCR catalyst. With vanadium-based SCR catalysts, a comparatively low ammonia level is advantageous for good NO2 reduction efficiency.

[0021] In an advantageous embodiment of the invention, the precious metal layers are formed from platinum or from mixtures of platinum and palladium, and the second precious metal content is higher than the first. Precious metal layers made of platinum and mixtures of platinum and palladium exhibit high NO₂ formation activity and a high catalytic effect for hydrocarbon oxidation. Furthermore, this embodiment of the invention is based on the following insight: The higher the precious metal content of a catalyst, the higher the reaction rate of NH₃ formed from the reducing agent to nitrous oxide (N₂O) compared to the reaction rate of NH₃ to N₂.Due to the lower precious metal content of the precious metal layer in the second catalyst section, any NH3 slip from the first SCR catalyst is advantageously oxidized to N2 instead of N2O in the second catalyst section. This means that no ammonia, or only a very small amount, reaches the third catalyst section, which serves as the oxidation section or oxidation catalyst. In the oxidation catalyst, any ammonia entering the catalyst would be more readily converted to N2O due to the higher precious metal content of the precious metal layer there; this is prevented by the second catalyst section.With this embodiment of the invention, emissions of climate-relevant N2O can be kept particularly low, while still providing a hot first SCR catalyst close to the combustion engine with the associated necessary addition of NH3 via a reducing agent upstream of an oxidation catalyst in the exhaust aftertreatment system.

[0022] In one embodiment of the invention, the precious metal layer of the second catalyst part has a high platinum content in a mixture of platinum and palladium compared to the precious metal layer of the third catalyst part, with a platinum content of at least 80 percent of the total mixture. The precious metal layer of the second catalyst part can also consist exclusively of platinum.

[0023] In one embodiment of the invention, the precious metal layer of the third catalyst part has a platinum content of at least 50 percent in a total mixture of platinum and palladium.

[0024] Furthermore, it has proven particularly advantageous if the first precious metal content is in a range from approximately 1 / 28316.8 grams per cubic centimeter to approximately 5 / 28316 grams per cubic centimeter. This means that the first precious metal content is preferably in a range from approximately 1 gram of precious metal per cubic foot to approximately 5 grams of precious metal per cubic foot, where one cubic foot corresponds at least substantially to 28316.8 cubic centimeters. With the first precious metal content of the second catalyst part according to this embodiment of the invention, any NH3 slip from the first SCR catalyst can advantageously be oxidized substantially to N2 instead of N2O, so that no ammonia or only a very small amount of ammonia reaches the third catalyst part, which is designed as an oxidation catalyst.

[0025] Finally, it has proven particularly advantageous if the second precious metal content is in the range of 5 / 28316.8 grams per cubic centimeter up to and including 20 / 28316.8 grams per cubic centimeter. With the second precious metal content of the third catalyst section according to this embodiment of the invention, a high oxidation rate of HC and a high oxidation rate of NO to NO₂ can advantageously be achieved in the third catalyst section. A high NO₂ content at the outlet of the combined catalyst, and thus before the exhaust gas enters the particulate filter, advantageously increases passive regeneration of the particulate filter with NO₂.

[0026] In a further embodiment of the invention, a first metering device is provided in the exhaust aftertreatment system, by means of which a reducing agent, in particular an aqueous urea solution, can be introduced into the exhaust gas at at least one first location arranged upstream of the combination catalyst, and thus upstream of the first SCR catalyst, for the purpose of denitrification. This allows the exhaust gas to be denitrified particularly effectively, so that emissions, in particular nitrogen oxide emissions, can be kept particularly low.

[0027] To keep nitrogen oxide emissions particularly low, a second metering device is provided in a further embodiment of the invention. This device allows a reducing agent, in particular an aqueous urea solution, to be introduced into the exhaust gas at at least one location downstream of the first SCR catalyst and upstream of the second catalyst for the purpose of denitrification. The second metering device is advantageously used to supply the reducing agent to the exhaust gas before it enters the second catalyst, which is designed as an SCR catalyst. This is necessary because, for the third catalyst section, which acts as an oxidation catalyst, the NH3 slip in the second catalyst section is oxidized, so that essentially no NH3 is present in the exhaust gas downstream of the second catalyst section of the combined catalyst, and thus also in the second catalyst, which is located downstream of the combined catalyst.In the following, the second catalyst of the exhaust aftertreatment device according to the invention, which is designed as an SCR catalyst, will be referred to as the second SCR catalyst.

[0028] By using the combination catalyst and arranging the metering devices according to this embodiment of the invention, NO2-based passive regeneration of the particulate filter can take place over particularly long periods or almost continuously, since during NO2-based regeneration of the particulate filter, when the metering of the reducing agent via the first metering device is switched off, the second metering device can be switched on or activated, and nitrogen oxide reduction can then occur with the second catalyst using the reducing agent introduced by the second metering device. Advantageously, this embodiment of the invention thus eliminates the time limit for nitrogen oxide reduction during NO2-based regeneration of the particulate filter that would be imposed by the NH3 storage capacity of the second SCR catalyst.

[0029] It has also proven particularly advantageous if the second point at which reducing agent can be introduced into the exhaust gas by means of the second metering device is located downstream of the particulate filter.

[0030] In a further embodiment of the invention, the particulate filter is provided with a coating that is free of heavy metals and precious metals and catalyzes the oxidation of the soot particles retained in the particulate filter. The heavy metal- and precious metal-free coating of the particulate filter provided in the exhaust aftertreatment device according to this embodiment of the invention advantageously contains no environmentally harmful heavy metals and no other toxic or environmentally damaging substances.

[0031] In a further embodiment of the invention, the heavy metal- and precious metal-free coating of the particulate filter comprises alkali and / or alkaline earth compounds. The heavy metal- and precious metal-free coating of the particulate filter can particularly advantageously contain alkali metal-containing silicates. Particulate filters with such a coating, which in particular contains alkali metal-containing silicates, can advantageously catalyze solid reactions with soot particles. The coating of the particulate filter has, for example, a silicate structure in which finely dispersed alkali metals, in particular potassium, are incorporated as the active component of the catalytic coating. The coating of the particulate filter can be applied to various substrates such as SiC or cordierite.

[0032] The coating of the particulate filter enables passive regeneration of the particulate filter based on nitrogen dioxide (NO2) even at very low levels of nitrogen dioxide and / or at lower temperatures, since the reaction of soot with nitrogen dioxide catalyzed by the coating with alkali and / or alkaline earth compounds, or the reaction of the soot particles contained in the particulate filter with nitrogen dioxide, is a solid-state reaction that is catalyzed, i.e., supported or brought about, by this coating. This reaction can occur at a particularly high rate.Under identical temperature conditions, in a particulate filter coated with alkali and / or alkaline earth compounds, the reaction of soot with nitrogen dioxide can occur at lower nitrogen dioxide concentrations and with higher reaction rates than in a particulate filter with a precious metal coating. Active, oxygen- (O2)-based soot oxidation or regeneration is also catalyzed more effectively by the alkali and / or alkaline earth compound coating and occurs at significantly lower temperatures in particulate filters with such a coating than in particulate filters with precious metal coatings. Therefore, even in the absence of NO2, particularly during the dosing of aqueous urea solution via the first dosing unit, soot is already oxidized to carbon dioxide (CO2) and water vapor (H2O) via O2 in the particulate filter.

[0033] Regeneration of the particulate filter means that at least some of the soot particles trapped in the filter are removed. With increasing operating time and thus with increasing soot particle retention from the exhaust gas, the particulate filter becomes increasingly clogged with soot particles. This clogging is also referred to as filter loading. During regeneration, the filter loading is reduced by oxidizing the soot particles. This means that the particulate filter is either oxidized with NO2 or burned clean with O2 during regeneration. Particulate filter coatings catalyze the oxidation of the soot particles.The coating of the particle filter with alkali and / or alkaline earth metal compounds enables NO2-based regeneration of the particle filter with significantly smaller amounts of NO2 and a higher reaction rate compared to particle filters with a precious metal-containing catalytic coating.

[0034] It was surprisingly found that coating the particulate filter with alkali metal-containing silicates particularly well catalyzes the regeneration of the particulate filter using NO2, so that such regeneration based on NO2, which is also referred to as passive regeneration, leads to a sufficient soot combustion rate even at low NO2 input concentrations, such as the raw NO2 emission of the internal combustion engine, and that it is advantageously not necessary to carry out NO2-based regeneration continuously in particulate filters with such a coating, but that intermittent regeneration is sufficient.

[0035] Since particulate filters with alkali and / or alkaline earth metal coatings undergo O2-based regeneration at significantly lower temperatures than particulate filters with precious metal coatings, O2-based regeneration in these filters will support NO2-based regeneration at temperatures of approximately 300 to 350 degrees Celsius. Within a temperature range of approximately 300 to 350 degrees Celsius, O2-based soot regeneration can also partially replace NO2-based regeneration if the latter is limited or completely ineffective due to low NO2 concentrations. This occurs when the total amount of NO2 present in the exhaust gas is consumed in the SCR reaction at the upstream first SCR catalyst formed by the first catalyst stage.Because O2-based regeneration in particulate filters with coatings containing alkali and / or alkaline earth metal compounds can already take place in a temperature range of approximately 300°C to 350°C, O2-based regeneration of the particulate filter can be used without the disadvantage of undesirable temperature-related damage to exhaust aftertreatment elements, which can occur at the high temperatures of O2-based regenerations of conventional precious metal-containing particulate filters. This is a crucial advantage for the exhaust aftertreatment device according to the invention, since SCR catalysts are particularly temperature-sensitive, and high temperatures during O2-based regeneration can thus be avoided in the first catalyst section of the exhaust aftertreatment device according to the invention.

[0036] As already indicated, it has proven particularly advantageous if the combination catalyst, especially the first catalyst part of the combination catalyst, is the first exhaust aftertreatment element downstream of the internal combustion engine through which the exhaust gas flows. In other words, the first catalyst part, especially the combination catalyst, is arranged as the first exhaust aftertreatment element through which the exhaust gas of the internal combustion engine flows after the exhaust gas exits the internal combustion engine, so that, with respect to the exhaust gas flow direction from the internal combustion engine to the first SCR catalyst, no exhaust aftertreatment element through which the exhaust gas flows is arranged between the combination catalyst, especially the first catalyst part, and the internal combustion engine for the purpose of treating the exhaust gas of the internal combustion engine.This prevents excessive cooling of the combination catalyst.

[0037] In one embodiment of the invention, the second and third catalyst parts form a hybrid catalyst, wherein the volume through which the exhaust gas flows in the second catalyst part is approximately twice the volume of the third catalyst part. It has surprisingly been found that the volume ratio of the second and third catalyst parts according to this embodiment of the invention is necessary so that, in particular, the exhaust aftertreatment system according to the invention can keep the concentration of newly formed N₂O so low that future emission requirements for secondary emissions can be met under real driving conditions.

[0038] The invention also includes a method for operating an exhaust aftertreatment device according to the invention. Advantageous embodiments of the exhaust aftertreatment device according to the invention are to be regarded as advantageous embodiments of the method according to the invention, and vice versa.

[0039] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0040] The drawing shows in: Fig. 1 a schematic side view of an exhaust aftertreatment device according to a first embodiment for an internal combustion engine of a motor vehicle, comprising at least one combination catalyst through which exhaust gas of the internal combustion engine flows, with at least one particulate filter through which exhaust gas flows and which is arranged downstream of the combination catalyst for retaining soot particles from the exhaust gas, and with an SCR catalyst through which exhaust gas flows and which is arranged downstream of the particulate filter; Fig. 2 a schematic side view of the exhaust aftertreatment device according to a second embodiment; Fig. 3. Partial schematic longitudinal section view of the combination catalyst; and Fig. 4 a diagram illustrating a method for operating the exhaust aftertreatment device;

[0041] In the figures, identical or functionally equivalent elements are provided with the same reference numerals.

[0042] Fig. Figure 1 shows a drive unit, designated as 10, for a commercial vehicle. The drive unit 10 comprises an internal combustion engine 12, which in this case is a reciprocating piston engine. The commercial vehicle can be driven by means of the internal combustion engine 12. The internal combustion engine 12 is designed as a diesel engine. The internal combustion engine 12 comprises a cylinder housing 14, through which a plurality of combustion chambers in the form of cylinders 16 of the internal combustion engine 12 are formed. During firing operation of the internal combustion engine 12, air and fuel, in particular liquid fuel, are supplied to the cylinders 16, so that a fuel-air mixture is formed in each cylinder 16. This fuel-air mixture is combusted, resulting in exhaust gas from the internal combustion engine.The exhaust gas from the cylinders 16 is guided in an exhaust manifold 18 and then discharged from the internal combustion engine 12.

[0043] The drive unit 10 further comprises an exhaust system 20, which is also referred to as the exhaust tract. The exhaust system 20 is permeable to the exhaust gases from the cylinders 16. The exhaust gases from the internal combustion engine 12 are conveyed by means of the exhaust system 20. The internal combustion engine 12 has a so-called outlet 22, through which the exhaust gas flows out of the internal combustion engine 12 and into the exhaust system 20. The outlet 22 is also referred to as the engine outlet or exhaust port and is located on an exhaust side of the internal combustion engine 12.

[0044] The exhaust system 20 comprises an exhaust aftertreatment device designated as a whole by 24, which is located in Fig. 1 according to a first embodiment. The exhaust gas from the internal combustion engine 12 is treated by means of the exhaust aftertreatment device 24. The exhaust system 20 and the exhaust aftertreatment device 24 are permeable to the exhaust gas, the flow of the exhaust gas through the exhaust system 20 and thus through the exhaust aftertreatment device 24 being Fig. Figure 1 is illustrated by arrows 26. With respect to the direction of exhaust gas flow through the exhaust system 20 and thus through the exhaust aftertreatment device 24, the exhaust aftertreatment device 24 is located downstream of the outlet 22. Since the exhaust gas upstream of the exhaust aftertreatment device 24 and downstream of the outlet 22 has not yet been treated by the exhaust aftertreatment device 24, the emissions from the internal combustion engine 12 in the area between the outlet 22 and upstream of the exhaust aftertreatment device 24 are referred to as raw emissions.

[0045] The exhaust aftertreatment system 24 comprises at least one first catalyst 32, designed as a combination catalyst, through which the exhaust gas from the internal combustion engine 12 flows, with at least one particulate filter 30, also through which the exhaust gas flows and which is arranged downstream of the first catalyst 32 for retaining soot particles from the exhaust gas, and a second catalyst 28, also through which the exhaust gas flows, which is arranged downstream of the particulate filter 30 and is designed as an SCR catalyst. The combination catalyst 32 is the first exhaust aftertreatment element through which the exhaust gas flows after the outlet 22 and thus after the exhaust gas exits the internal combustion engine 12.This means that the combination catalyst 32 is the first exhaust aftertreatment element downstream of the internal combustion engine 12, through which the exhaust gas flows, so that between the combination catalyst 32 and the internal combustion engine 12, in particular the outlet 22, no exhaust aftertreatment element through which the exhaust gas is treated is arranged.

[0046] The drive unit 10 further comprises a Fig. 1 exhaust gas turbocharger, also referred to as a turbocharger, which is not shown in its entirety. Furthermore, the drive unit 10 includes, for example, a Fig. 1. Intake tract (not shown), through which the aforementioned air or a mixture of recirculated exhaust gas and air supplied to cylinders 16 can flow. The exhaust gas turbocharger comprises a compressor arranged in the intake tract, by means of which the air flowing through the intake tract and supplied to cylinders 16, or the mixture of recirculated exhaust gas and air, is to be compressed, or is compressed.

[0047] Furthermore, the exhaust gas turbocharger comprises a turbine 34, which is arranged in the exhaust system 20 and is therefore permeable to the exhaust gas flowing through the exhaust system 20. With respect to the direction of exhaust gas flow through the exhaust system 20, the turbine 34 is arranged upstream of the combination catalyst 32. The turbine 34 comprises, for example, a turbine housing 36 and a turbine wheel 38 arranged in the turbine housing 36 and driven by the exhaust gas flowing through the turbine 34, which is rotatable about an axis of rotation relative to the turbine housing 36. The compressor comprises, for example, a compressor wheel by means of which the air flowing through the intake tract can be compressed. The compressor wheel is, for example, arranged coaxially to the turbine wheel 38 and is thus rotatable about the aforementioned axis of rotation. The exhaust gas turbocharger further comprises a Fig. 1. A shaft (not shown) is connected in a rotationally fixed manner to both the turbine wheel 38 and the compressor wheel. This allows the compressor wheel to be driven by the turbine wheel 38 via the shaft. Since the turbine wheel 38 can be driven by the exhaust gas, and since driving the compressor wheel compresses the air flowing through the intake tract, energy contained in the exhaust gas can be used to compress the air, thus enabling particularly efficient operation of the drive unit 10.

[0048] The retention of soot particles from the exhaust gas by means of the particulate filter 30 means that the particulate filter 30 filters out and thus retains soot particles contained in the exhaust gas. After the exhaust gas exits the internal combustion engine 12, it contains soot particles, which are at least partially filtered out by the particulate filter 30. The soot particles adhere to the particulate filter 30, particularly inside it, and are deposited there, so that the particulate filter 30 becomes increasingly clogged with soot particles over time. This clogging is also referred to as the loading or clogging of the particulate filter 30. If the internal combustion engine 12 is, for example, a diesel engine, the particulate filter 30 is also referred to as a diesel particulate filter (DPF).

[0049] To achieve particularly low-emission operation, the combination catalyst 32 comprises – as is particularly well seen in combination with Fig. 3 is recognizable - a first catalyst part 40, which is designed as the first SCR catalyst.

[0050] The first SCR catalyst is designed as a vanadium-based SCR catalyst, with vanadium also being denoted by Va. Therefore, and because an SCR catalyst is generally simply referred to as SCR, the first catalyst part is 40 in Fig. 3 also referred to as Va-SCR.

[0051] The combination catalyst 32 further comprises a second catalyst part 42, arranged downstream of the first catalyst part 40 in the direction of exhaust gas flow through the combination catalyst 32. This second catalyst part 42 is designed as an ammonia slip catalyst (ASC) and has a precious metal layer 44 formed exclusively with platinum and containing a certain amount of platinum. The precious metal layer 44 of the second catalyst part 42 can also be formed with a precious metal mixture of platinum and palladium, wherein the platinum content in the platinum-palladium mixture is at least 80 percent.Furthermore, the combination catalyst 32 comprises a third catalyst part 46, arranged downstream of the second catalyst part 42 in the direction of exhaust gas flow through the combination catalyst 32. This third catalyst part 46 is designed as an oxidation catalyst and has a precious metal layer 48, which is also composed exclusively of the precious metal platinum and contains a second platinum component. The precious metal layer 48 of the third catalyst part 42 can also be composed of a precious metal mixture of platinum and palladium instead of pure platinum, with the platinum content in the platinum-palladium mixture being at least 50 percent. Since the internal combustion engine 12 is, for example, a diesel engine, the oxidation catalyst is also referred to as a diesel oxidation catalyst (DOC).Furthermore, the combination catalyst 32 comprises an SCR layer 50 arranged on the respective platinum layers 44 and 48, which comprises copper (Cu) and zeolite (Z) and is therefore also referred to as the Cu-Z layer.

[0052] The respective platinum layers 44 and 48 are layers that comprise platinum (Pt). The first platinum content is located in the Fig. 3 combination catalyst 32 shown in a range of including 1 gram per cubic foot (g / ft³) 3 ) up to and including 5 grams per cubic foot, with the second platinum content ranging from 5 grams per cubic foot up to and including 20 grams per cubic foot. One cubic foot (ft³) corresponds to 3 ) at least substantially 28316.8 cubic centimeters (cm³) 3 ) and denotes the volume of the respective platinum layer 44 or 48. It has proven particularly advantageous if the second platinum content is higher than the first platinum content.

[0053] Out of Fig. 3 It can be seen that the second catalyst part 42 and the third catalyst part 46, as well as the SCR layer 50, form a hybrid catalyst designated as a whole 52, which exhibits both an ammonia slip effect (ASC effect) and an oxidation effect (DOC effect), so that the combination catalyst can also be called hybrid-ASC-DOC in Fig. The hybrid catalyst 52 is designated as 3. The hybrid catalyst 52 has a total length L extending in the direction of exhaust gas flow. The second catalyst part 42 has a first partial length l1 extending in the direction of exhaust gas flow, and the third catalyst part 46 has a second partial length l2 extending in the direction of exhaust gas flow. The partial lengths l1 and l2 add up to the total length L. The SCR layer 50 extends over the entire length L of the hybrid catalyst 52, and thus over the partial length l1 of the second catalyst part 42 and the partial length l2 of the third catalyst part 46. In this case, the first partial length l1 is two-thirds of the total length L, and the partial length l2 is one-third of the total length L. The combination catalyst 32 as a whole has a length G extending in the direction of exhaust gas flow, and the first catalyst part 40 has a partial length t extending in the direction of exhaust gas flow.

[0054] The partial length t and the total length L sum to the length G of the combination catalyst 32. It is provided, for example, that the partial length t lies in a range from 50 percent to 90 percent of the length G, and that the total length L lies, for example, in a range from 10 percent to 50 percent of the length G.

[0055] The SCR layer 50, located on platinum layers 44 and 48, is designated as such and is, for example, a copper-zeolite layer (Cu-Z layer). The term SCR layer 50 refers to the fact that it performs SCR action. This means that SCR layer 50 catalyzes, or facilitates, a selective catalytic reduction (SCR) process in which nitrogen oxides in the exhaust gas are converted into nitrogen and water.

[0056] Out of Fig. Figure 3 shows that the SCR layer 50 is an upper layer or coating arranged on, or applied to, the platinum layers 44 and 48. The SCR layer 50 is applied directly to the platinum layers 44 and 48, so that it is in contact with them. The lower platinum layer 44 of the second catalyst part 42 serves to oxidize excess ammonia (NH3), so that the second catalyst part 42 functions as an ammonia slip catalyst. The rear platinum layer 48 serves to oxidize NO and unburned hydrocarbons (HC), so that NO2, for example, is formed by means of the platinum layer 48 to achieve passive soot combustion, i.e., passive regeneration of the particulate filter 30, and to provide a sufficient temperature for active regeneration of the particulate filter 30.Passive regeneration is an NO2-based regeneration process that at least reduces the loading of the particulate filter 30. The aforementioned active regeneration is an oxygen-based (O2-based) regeneration process that also at least reduces the loading of the particulate filter 30. The respective platinum layers 44 and 48 are lower platinum layers located beneath the SCR layer 50. The goal for both platinum layers 44 and 48 is low N2O selectivity.

[0057] In particular, it is conceivable that the partial length l1 lies within a range of 0 percent to 80 percent of the total length L, inclusive. Furthermore, it is conceivable that the partial length l2 lies within a range of 20 percent to 100 percent of the total length L, inclusive.

[0058] The drive unit 10, in particular the exhaust aftertreatment unit 24, comprises a first metering unit 54 by means of which a reducing agent for denitrification of the exhaust gas can be introduced into the exhaust gas at at least one first location S1 arranged upstream of the combination catalyst 32. The reducing agent is, for example, an aqueous urea solution from which ammonia is produced, which can react with nitrogen oxides contained in the exhaust gas to form water and nitrogen within the framework of the aforementioned SCR. Fig. Figure 1 shows that the first position S1, or the metering device 54, is arranged upstream of the turbine wheel 38 or the turbine 34. However, it is preferred that the first position S1, or the first metering device 54, is arranged upstream of the combination catalyst 32 and downstream of the turbine wheel 38 or the turbine 34.

[0059] Furthermore, a second metering device 56 is provided, by means of which reducing agent for denitrification of the exhaust gas can be introduced into the exhaust gas at at least one second location S2 arranged downstream of the combination catalyst 32 and upstream of the SCR catalyst 28. By converting the nitrogen oxides contained in the exhaust gas into water and nitrogen as described above, the nitrogen oxides are at least partially removed from the exhaust gas. This removal of the nitrogen oxides is also referred to as denitrification of the exhaust gas, which – as described – is carried out with the help of the reducing agent. In the Fig. In the first embodiment shown in Figure 1, the second position S2 or the second metering device 56 is arranged upstream of the SCR catalyst 28 and upstream of the particle filter 30.

[0060] Downstream of the second point S2, or the second metering device 56, and upstream of the SCR catalyst 28, a mixing device 58 is arranged by means of which the metered reducing agent is mixed with the exhaust gas. In the first embodiment, the mixing device 58 is arranged upstream of the particulate filter 30. Furthermore, the exhaust aftertreatment device 24 comprises a catalyst 60, which is arranged downstream of the SCR catalyst 28 and is configured as an SCR catalyst and / or as an ammonia slip catalyst.

[0061] To achieve particularly low-emission operation, the particulate filter 30 is equipped with a heavy-metal- and precious-metal-free coating based on alkali metal silicate structures. This coating catalyzes the oxidation of the soot particles retained within the particulate filter 30. The coating is therefore composed of silicates containing alkali metals. This coating catalyzes soot oxidation, i.e., the oxidation of the soot particles retained by the particulate filter 30, with exceptional efficiency and effectiveness. This oxidation process removes the soot particles from the particulate filter 30, thereby reducing the soot load. This reduction of the particulate filter 30's load is also referred to as regeneration.

[0062] Fig. Figure 2 shows a second embodiment of the drive device 10. Fig. For clarity, the internal combustion engine 12 is not shown in Figure 2. The second embodiment differs from the first embodiment in particular in that the second position S2, or the second metering device 56, is arranged upstream of the SCR catalyst 28, but downstream of the particulate filter 30. The mixing device 58 is arranged downstream of the second position S2, or the second metering device 56, and upstream of the SCR catalyst 28.

[0063] Furthermore, an HC doser (not shown in the figure) can be provided, by means of which unburned hydrocarbons can be introduced into the exhaust gas at a dosing point D. Fig. 1 and Fig. As can be seen from Figure 2, the metering point D, or the HC metering device, is arranged upstream of the combination catalyst 32 and, for example, preferably downstream of the turbine wheel 38 or the turbine 34. Alternatively, it is conceivable that the HC metering device, or the metering point D, at which the unburned hydrocarbons (HC) can be introduced or metered into the exhaust gas by means of the HC metering device, is arranged upstream of the combination catalyst 32 and, in particular, upstream of the turbine wheel 38 or the turbine 34. Alternatively or additionally to the use of the HC metering device, in-engine measures for introducing unburned hydrocarbons into the exhaust gas are conceivable. One such in-engine measure is, for example, a particularly late injection of fuel into at least one of the cylinders 16.

[0064] The catalyst volumes of the combination catalyst 32, as well as the volumes of catalyst parts 40, 42 and 46, and those of catalysts 28 and 60, are determined by the displacement of the internal combustion engine 12. The first catalyst part 40, made of Fig. 1 or Fig. 2 has a volume through which the exhaust gas can flow, which for commercial vehicle internal combustion engines is in the range of approximately 44 to 105 percent of the displacement volume of the internal combustion engine 12. The sum of the volumes of the SCR catalyst 28 and the catalyst 60 is in the range of approximately 78 to 179 percent of the displacement volume of the internal combustion engine 12 for commercial vehicle internal combustion engines. The ratio of the volume of the first catalyst part 40 to the sum of the volumes of the SCR catalyst 28 and the catalyst 60, for example, is in the range of 0.25 inclusive to 1.34 inclusive.

[0065] The following describes, for example, a start condition for the passive, NO2-based regeneration of the particulate filter 30: If, for example, the SCR catalyst 28 has a sufficient temperature, for example in the range of 200 degrees Celsius to 250 degrees Celsius, the first metering device 54 is switched off, so that NO2 formed in the engine is not converted at the first SCR, and additional NO2 formation takes place via the hybrid catalyst 52. The following describes stop conditions for passive regeneration: If, for example, the temperature of the SCR catalyst 28 falls below a predefinable threshold value, for example in the range of 180 degrees Celsius to 220 degrees Celsius, the first metering device 54 is activated, so that nitrogen oxide conversion takes place at low exhaust gas temperatures via the first catalyst section 40, which functions as an SCR catalyst.Alternatively or additionally, the stop condition includes that the space velocity of the SCR catalyst 28 exceeds a predefinable threshold, for example in a range of 40,000 to 60,000 and / or that a storage rate exceeds a threshold and / or that the nitrogen oxide content exceeds a predefinable threshold.

[0066] The regeneration duration of active regeneration, for example, ranges from 15 minutes to 60 minutes and is carried out, for example, after an interval of more than 100 hours. The size fraction of the first catalyst section 40 in relation to the total SCR volume of the exhaust aftertreatment system 24, for example, ranges from 20 percent to 50 percent. The following describes parameters that trigger passive, NO2-based regeneration. For example, the condition of the first metering unit 54 is the parameter that triggers passive regeneration.

[0067] The following parameters describe what triggers active, O2-based regeneration: - Model-based soot loading limit (soot quantity trigger) - Maximum duration without regeneration approximately 100 hours (time trigger) - Back pressure > factor 2 compared to an empty filter (back pressure trigger) - favorable temperatures > 300 degrees Celsius + minimum soot quantity (5 grams per liter) (temperature trigger).

[0068] The following parameters explain which interrupt or terminate a regeneration: - Soot quantity < 1 gram per liter - Back pressure < 1.1 against empty filter.

[0069] Fig. Figure 4 shows a diagram illustrating a method for operating the drive unit 10, in particular the exhaust aftertreatment unit 24. The diagram in Fig. Diagram 4 shown has an abscissa 62 on which time, in particular in seconds, is plotted. Furthermore, the diagram has an ordinate 64 on which temperature, in particular in degrees Celsius, is plotted. A curve 66 is shown in the diagram, illustrating the temperature of the first catalyst part 40, which is also referred to as ccSCR. In other words, curve 66 is a time course of the temperature of the first catalyst part 40, which functions as an SCR catalyst. A line 68 illustrates a state of the first metering device 54. When blocks 70 and 72 are shown in line 68, the first metering device 54 is activated, so that blocks 70 and 72 illustrate respective time intervals during which the reducing agent is introduced, in particular injected, into the exhaust gas by means of the activated first metering device 54.

[0070] Line 74 illustrates a state of the second metering device 56, wherein blocks 76 and 78 entered in line 74 indicate that the second metering device 56 is activated. Thus, blocks 76 and 78 illustrate respective time intervals during which the reducing agent is introduced, in particular injected, into the exhaust gas by means of the activated second metering device 56. Line 80 illustrates a state of the HC doser or the activation of in-engine measures to increase the exhaust gas temperature. Block 82 entered in line 80 illustrates a time interval during which the HC doser is activated, such that during the time interval illustrated by block 82, unburned hydrocarbons (HC) are introduced, in particular injected, into the exhaust gas at metering point D by means of the activated HC doser. Furthermore, line 84 of the diagram illustrates the raw nitrogen oxide emissions of the internal combustion engine 12.Blocks 86, 88, and 90, entered in line 84, illustrate internal combustion engine measures for nitrogen oxide reduction. Since the internal combustion engine 12 is also referred to as an internal combustion engine, these internal combustion engine measures are also called internal combustion engine measures or VM measures.

[0071] Thus, blocks 86, 88, and 90 illustrate the respective time periods during which internal combustion engine measures are implemented to reduce nitrogen oxides (NOx), i.e., to eliminate NOx. One such measure is, for example, retarding the injection timing. Another measure could be a particularly high exhaust gas recirculation rate. A further measure is, for example, reducing the mass airflow supplied to cylinder 16, which is achieved, for instance, by throttling. This is done, for example, by means of a throttle valve located in the intake manifold. A further measure could be operating the engine at higher loads.

[0072] Block 92, shown in the diagram, illustrates a start, in particular a cold start, of the internal combustion engine 12. During this cold start, at least one internal combustion engine operation is performed, as illustrated by block 86. Block 94, shown in the diagram, illustrates a heating phase, during which – as can be seen from block 70 – the first metering device 54 is activated. This is followed by a fuel-efficiency phase, illustrated by block 96. Block 98 illustrates operation of the internal combustion engine 12 at low loads, during which at least one internal combustion engine operation, illustrated by block 88, is performed.

[0073] Furthermore, the metering device 54 is activated (block 72), or in-engine measures are triggered. This is followed by a fuel-efficiency-optimized phase, illustrated by block 100, during which, for example, the HC doser is activated (block 82). Furthermore, as illustrated by block 90, at least one combustion engine measure is carried out. It is preferably provided that the HC doser is only activated when the first metering device 54 is deactivated, i.e., when the introduction of reducing agent into the exhaust gas by the metering device 54 is prevented. If the respective metering device 54 or 56 is deactivated, the introduction of reducing agent into the exhaust gas by the respective metering device 54 or 56 is prevented. If the HC doser is activated, unburned hydrocarbons (HC) are introduced into the exhaust gas by means of the HC doser.If the HC doser is deactivated, no HC is introduced into the exhaust gas by the HC doser.

[0074] Furthermore, illustrated in Fig. 4 a double arrow 102 the passive regeneration or a regeneration duration of the passive regeneration, where a double arrow 104 illustrates the active regeneration or the regeneration duration of the active regeneration.

Claims

[1] Exhaust aftertreatment device (24) for an internal combustion engine (12) of a motor vehicle, comprising at least one first catalyst (32) through which exhaust gas from the internal combustion engine (12) flows, comprising at least one particulate filter (30) through which exhaust gas flows and which is arranged downstream of the first catalyst (32) for retaining soot particles from the exhaust gas, and a second catalyst (28) through which at least the exhaust gas flows, which is arranged downstream of the particulate filter (30) and is designed as an SCR catalyst, characterized by , that the first catalyst (32) is a combination catalyst, with - a first catalyst part (40) which is designed as an SCR catalyst; - a second catalyst part (42) arranged downstream of the first catalyst part (40), which is designed as an ammonia slip catalyst and has a precious metal layer (44) with a first precious metal content; - a third catalyst part (46) arranged downstream of the second catalyst part (42), which is designed as an oxidation catalyst and has a precious metal layer (48) with a second precious metal content; and - an SCR layer (50) which is arranged on the precious metal layers (44, 48) of the second and third catalyst part (42, 46) and extends over the entire length (L) of the second and third catalyst part (42, 46). [2] Exhaust aftertreatment device (24) according to claim 1, characterized by , that the precious metal layers (44, 48) of the second and third catalyst part (42, 46) are formed from platinum or from mixtures of platinum and palladium and that the second precious metal content is higher than the first precious metal content. [3] Exhaust aftertreatment device (24) according to claim 2, characterized by, that the precious metal layer (48) of the third catalyst part (46) has a platinum content of at least 50 percent in the mixture of platinum and palladium. [4] Exhaust aftertreatment device (24) according to one of the preceding claims, characterized by , that the first precious metal content is in a range from inclusive of 1 gram of precious metal per cubic foot to inclusive of 5 grams of precious metal per cubic foot. [5] Exhaust aftertreatment device (24) according to one of the preceding claims, characterized by , that the second precious metal content is in a range from inclusive of 5 grams of precious metal per cubic foot to inclusive of 20 grams of precious metal per cubic foot. [6] Exhaust aftertreatment device (24) according to one of the preceding claims, characterized by , that the particle filter (30) is provided with a coating free of heavy metals and precious metals and which catalyzes the oxidation of the soot particles retained in the particle filter (30), [7] Exhaust aftertreatment device (24) according to claim 6, characterized by , that the heavy metal and precious metal-free coating of the particle filter (30) contains all-kali and / or alkaline earth metal compounds. [8] Exhaust aftertreatment device (24) according to one of the preceding claims, characterized by , that a first metering device (54) is provided by means of which a reducing agent for denitrification of the exhaust gas can be introduced into the combination catalyst (32) at at least one first location (S1) arranged upstream of the combination catalyst (32). [9] Exhaust aftertreatment device (24) according to claim 8, characterized by , that a second metering device is provided, by means of which a reducing agent for denitrification of the exhaust gas can be introduced into it at at least one second location (S2) arranged downstream of the combination catalyst (32) and upstream of the second catalyst (28). [10] Exhaust aftertreatment device (24) according to one of the preceding claims, characterized by , that the combination catalyst (32), in particular the first catalyst part (40) of the combination catalyst (32) designed as an SCR catalyst, is the first exhaust aftertreatment element downstream of the internal combustion engine (12) through which the exhaust gas can flow. [11] Exhaust aftertreatment device (24) according to one of the preceding claims, characterized by , that the second catalyst part (42) and the third catalyst part (46) form a hybrid catalyst (52), wherein the volume through which the exhaust gas can flow in the second catalyst part (42) is approximately twice the volume of the third catalyst part (46).

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