DE102020207311B4 - Ammonia slip catalyst, exhaust aftertreatment system and exhaust aftertreatment method - Google Patents

Abstract

Ammonia blocking catalytic converter (40) for arrangement in an exhaust system (22) of an internal combustion engine (10), comprising an oxidation zone (42) for oxidizing ammonia, a mixing space (86) for mixing ammonia and an oxidation product of the ammonia and, in the direction of flow of the Oxidation zone (42) and the mixing space (86) downstream SCR catalyst (44).

Description

The invention relates to an ammonia blocking catalyst, an exhaust aftertreatment system with such an ammonia blocking catalyst and a method for exhaust aftertreatment of an internal combustion engine with such an exhaust aftertreatment system according to the preamble of the independent patent claims.

The current exhaust gas legislation and one that will become increasingly strict in the future place high demands on engine raw emissions and the exhaust gas aftertreatment of combustion engines. The demands for a further reduction in consumption and the further tightening of the exhaust gas standards with regard to the permitted nitrogen oxide emissions represent a challenge for the engine developers. Catalyst upstream and downstream further catalysts. Exhaust gas aftertreatment systems are currently used in diesel engines, which have an oxidation catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for separating soot particles and optionally further catalytic converters. Ammonia is preferably used as the reducing agent. Because handling pure ammonia is complicated, vehicles usually use a synthetic, aqueous urea solution, which is mixed with the hot exhaust gas flow in a mixing device upstream of the SCR catalytic converter. This mixing heats up the aqueous urea solution, with the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution is generally made up of 32.5% urea and 67.5% water.

Furthermore, exhaust gas aftertreatment systems are known with at least two exhaust gas aftertreatment components for the selective, catalytic reduction of nitrogen oxides, through which an exhaust gas stream of the internal combustion engine flows sequentially, the first exhaust gas aftertreatment component being arranged close to the engine and the second exhaust gas aftertreatment component being arranged under the floor of a motor vehicle, with each exhaust gas aftertreatment component having a metering element for metering in is assigned aqueous urea solution in order to be able to operate at least one exhaust gas aftertreatment component in a temperature range, depending on the operating situation of the internal combustion engine, in order to enable efficient conversion of the nitrogen oxide emissions.

Every device for catalytic exhaust gas purification requires a minimum temperature, the so-called light-off temperature, to be exceeded in order to be effective. During a cold start of a motor vehicle, the temperature level of the internal combustion engine and the components for exhaust gas aftertreatment is approximately at ambient temperature. Even with a high energy input into the exhaust system, the thermally inertial mass of the exhaust system must first be overcome and the radiation or convection losses compensated in order to achieve at least partial effectiveness of the exhaust gas aftertreatment components. During this time, the raw emissions from the internal combustion engine are emitted largely untreated. Depending on the energy input into the exhaust system, this period can be shortened, but never reduced to zero.

In diesel engines, it is known to place a NOx storage catalytic converter upstream of an SCR exhaust gas cleaning system, which already achieves good conversion performance in the range of 120 - 200°C, while the SCR catalytic converter only enables nitrogen oxide emissions to be converted from around 180°C. The exhaust gas aftertreatment components can be supported individually or as a whole during their heating phase, in particular up to the respective light-off temperature, by electrical heating elements or thermal exhaust gas burners. If more reducing agent is metered in than is reacted with the nitrogen oxides (NOx) during the reduction, undesirable ammonia slip may occur. In the prior art, the removal of the ammonia is achieved by an additional oxidation catalytic converter behind the SCR catalytic converter. This blocking catalyst oxidizes any ammonia that may occur to form molecular nitrogen (N2) and water vapor (H2O). In addition, careful application of the urea dosage is essential.

the DE 11 2015 002 186 T5 discloses an ammonia slip catalyst having a high porosity substrate containing platinum, palladium or a mixture thereof in the walls of the high porosity substrate. Further, the ammonia slip catalyst has an SCR catalyst coating on a wall of the high porosity substrate. The platinum, palladium or mixture thereof may be present in the wall of the high porosity support in the form of a metal or in the form of supported platinum, palladium or a mixture thereof. The catalytic articles are useful for selective catalytic reduction (SCR) of NOX in exhaust gases and reducing the amount of ammonia slip.

From the DE 10 2010 050 312 A 1, an ammonia oxidation catalyst with low nitrous oxide (N2O) by-product formation is known. The aim of ammonia oxidation in the slip catalyst is to oxidize the ammonia to form molecular nitrogen. The reaction of the over-oxidized components NOx and N2O with the SCR catalytic converter is then slower and not uniform for NOx and N2O. It is therefore difficult to keep both the NOx replica in this catalyst and the N2O emissions low. This is achieved by an ammonia slip catalyst catalytic composition comprising a noble metal on an acidic tungsten-containing mixed oxide.

the DE 10 2016 111 148 A1 discloses an ammonia slip catalyst having an ammonia oxidation catalyst comprising a platinum group metal and a first SCR catalyst comprising a metal exchange molecular sieve, vanadium, a base metal, an oxide of a base metal, or a mixed oxide. The ammonia oxidation catalyst and the SCR catalyst can be in one of four configurations: three types of bilayer configurations and a mixture. In the first bi-layer configuration, the ammonia oxidation catalyst is in a lower layer and an SCR catalyst is in the upper layer. In the second bilayer configuration, the SCR catalyst is in a layer in front of a layer comprising the ammonia oxidation catalyst. In the third bilayer configuration, the SCR catalyst is in a layer in front of a layer comprising the ammonia oxidation catalyst and a portion of the SCR catalyst is also present in an upper layer above the ammonia oxidation catalyst.

From the DE 10 2008 025 761 A1 a metallic carrier for a catalytic converter or a particle filter and the use of a metallic carrier for cleaning exhaust gas from diesel engines is known. The metal carrier essentially consists of an aluminum alloy with an aluminum content of 75 to 100 percent by mass. With the aid of the metallic carrier according to the invention, an advantageous reduction in carrier mass and heat capacity is achieved, as a result of which the light-off temperature (“light-off”) is reached more quickly. The reduction in mass and heat capacity is not at the expense of a reduction in the catalytic support surface area.

the DE 10 2016 111 147 A1 discloses an exhaust aftertreatment system for an internal combustion engine with an SCR catalyst and an ammonia slip catalyst. The exhaust aftertreatment system has a first zone with a first SCR catalytic converter and a second zone with an ammonia slip catalytic converter (ASC). The ammonia slip catalyst includes a second SCR catalyst and an oxidation catalyst, and has an oxidation function for unburned hydrocarbons (HC) and carbon monoxide (CO). The first zone of the ammonia barrier catalyst is arranged on the inlet side of the substrate and the second zone is arranged on the outlet side of the substrate. The exhaust aftertreatment system includes a catalyst for selective catalytic reduction (SCR) of nitrogen oxides, to reduce the amount of ammonia slip and to oxidize organic residues (HC, CO) in the exhaust stream of the internal combustion engine.

Furthermore, from the DE 10 2008 055 890 A1 a particulate filter with a porous carrier body, an SCR-active component and an oxidation catalyst is known, the SCR-active component being present as a coating on the exhaust gas inlet surface and the inner surface of the porous carrier body and the oxidation catalyst as a coating on the exhaust gas outlet surface of the porous carrier body.

the DE 10 2014 221 322 A1 discloses an exhaust gas treatment device for an exhaust system of an internal combustion engine for a motor vehicle. The exhaust gas treatment device comprises a dosing element for introducing a reducing agent for nitrogen oxides into the exhaust system, an SCR catalytic converter arranged downstream of the dosing element in the exhaust system for the selective catalytic reduction of nitrogen oxides, a passive mixing element which is arranged in direct fluidic connection upstream of the SCR catalytic converter, and a particle filter with an oxidation-catalytically active coating arranged in direct fluidic connection downstream of the SCR catalytic converter in the exhaust system.

From the EP 3 636 890 A1 an exhaust aftertreatment system for an internal combustion engine is known. The exhaust aftertreatment system comprises an exhaust system in which a diesel particulate filter, an SCR catalytic converter downstream of the diesel particulate filter and an ammonia blocking catalytic converter downstream of the SCR catalytic converter are arranged. The diesel particulate filter is free of platinum or palladium, but coated with rhodium and the ammonia slip catalytic converter is coated with platinum.

A disadvantage of the solutions known from the prior art, however, is that at high exhaust gas temperatures above approximately 380° C., ammonia stored in the SCR catalytic converter can be released. At this temperature it is not or not sufficiently possible to stick the released ammonia into molecular to convert substance and water vapor so that nitrogen oxides and/or nitrous oxide are formed from the ammonia during a chemical reaction on the blocking catalyst. As a result, the tailpipe emissions from limited exhaust gas components can increase, meaning that the increasingly strict exhaust gas legislation can no longer be complied with.

The object of the invention is now to reduce the formation of secondary emissions by the ammonia blocking catalytic converter and thus to minimize the tailpipe emissions of a motor vehicle with an internal combustion engine.

This object is achieved by an ammonia slip catalyst for arrangement in an exhaust system of an internal combustion engine, which comprises an oxidation zone for oxidizing ammonia, a mixing chamber for mixing ammonia and an oxidation product of the ammonia, and an SCR catalyst downstream of the oxidation zone and the mixing chamber in the direction of flow . As a result, ammonia released in the exhaust aftertreatment, in particular ammonia thermally discharged from an SCR catalytic converter, can be partially oxidized and converted into molecular nitrogen and water vapor with the remaining ammonia by a downstream SCR catalytic converter. In this case, ammonia discharged from an SCR catalytic converter does not result in this ammonia being converted into nitrogen oxides by the ammonia barrier catalytic converter at high temperatures, which leads to an increase in nitrogen oxide tailpipe emissions. Thus, even at high loads and the associated high exhaust gas temperatures, it can be ensured that the ammonia blocking catalytic converter keeps both the ammonia and the nitrogen oxide tailpipe emissions below the applicable limit values.

The features listed in the dependent claims allow advantageous further developments and improvements of the ammonia blocking catalyst listed in the independent claim.

In a preferred embodiment of the invention, it is provided that the oxidation zone, the mixing space and the downstream SCR catalytic converter are arranged in a common housing. The installation of the exhaust system can be simplified by arranging the oxidation stage, the mixing chamber and the SCR catalytic converter in a common housing.

In an advantageous embodiment of the ammonia barrier catalytic converter, it is provided that the SCR catalytic converter is designed as an SCR disk. An SCR disc can be easily and inexpensively manufactured and integrated into an ammonia slip catalyst.

In a preferred embodiment of the ammonia slip catalyst, it is provided that the oxidation zone has a plurality of first channels and a plurality of second channels, the first channels being provided with a precious metal coating and the second channels being uncoated or the second channels having a precious metal coating are provided and the first channels are uncoated. As a result, a portion of the ammonia released upstream of the ammonia slip catalyst is converted into nitrogen oxides, which can be converted into water vapor and molecular nitrogen in the downstream SCR catalyst with the ammonia remaining in the exhaust gas flow. Thus, the exhaust emissions of a motor vehicle can be minimized even under unfavorable load conditions.

It is preferred if the first channels and the second channels run essentially parallel to one another. As a result, approximately the same volume of exhaust gas flows through the first channels and the second channels, so that a favorable ratio of nitrogen oxides and ammonia is established upstream, in order to convert the nitrogen oxides and ammonia into unlimited exhaust gas components as part of a selective, catalytic reduction convert.

In an advantageous improvement of the ammonia blocking catalytic converter, it is provided that the ammonia blocking catalytic converter is designed as a double wrapped film at least in the region of the oxidation zone, with the two wrapped films forming the first channels and the second channels. A particularly simple and cost-effective production of an ammonia blocking catalytic converter is possible by means of a double wrapping film. Coating the foils on one side can ensure that approximately half the exhaust gas volume flows through a duct in the oxidation zone coated with a precious metal coating and the other half of the exhaust gas volume flows through an uncoated duct. The ratio of the uncoated and coated channels can be adjusted accordingly in order to achieve the most efficient possible selective, catalytic reduction of the nitrogen oxides by the remaining ammonia.

In an advantageous improvement of the invention, it is provided that the double wrapping film is designed as a perforated wrapping film, which enables gas exchange between the first channels and the second channels. A perforated wrapping film enables gas exchange between tween the channels, so that a mixing space can be formed in a simple manner. As a result, a particularly compact design of the ammonia blocking catalyst is possible.

In an advantageous embodiment of the ammonia barrier catalytic converter, it is provided that the region of the double wrapping foil lying downstream of the oxidation zone in the direction of flow is provided with an SCR coating and forms the SCR catalytic converter. As a result, the ammonia barrier catalyst can be designed with only one monolith, which means that the production costs can be reduced.

In an alternative embodiment of the ammonia barrier catalytic converter, it is advantageously provided that the first channels and the second channels open into the mixing chamber, with the mixing chamber promoting mixing of the oxidation product with the ammonia. This enables particularly efficient mixing of ammonia and nitrogen oxides before they enter the SCR catalytic converter of the ammonia blocking catalytic converter, as a result of which particularly high efficiency in the selective, catalytic reduction and thus minimal tailpipe emissions are achieved.

It is particularly preferred if an exhaust gas mixer is arranged in the mixing space. The mixing of ammonia and nitrogen oxides in the mixing space can be further improved by an exhaust gas mixer in the mixing space, which increases the efficiency of the ammonia blocking catalytic converter.

In an advantageous embodiment of the ammonia barrier catalytic converter, it is provided that a coolant connection for a cooling circuit of the internal combustion engine is formed on the housing and the coolant of the internal combustion engine flows through the housing. A coolant connection can reduce the exhaust gas temperature when flowing through the oxidation zone of the ammonia blocking catalytic converter, so that the tendency to form nitrogen oxides from the ammonia released upstream of the ammonia blocking catalytic converter is reduced.

A further aspect of the invention relates to an exhaust gas aftertreatment system for an internal combustion engine, comprising an exhaust system with an exhaust gas duct, in which a first catalytic converter close to the engine, a particle filter and at least one exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides are arranged in the flow direction of an exhaust gas stream of the internal combustion engine through the exhaust gas duct . In this case, such an ammonia blocking catalytic converter is arranged downstream of the last exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides SCR catalytic converter. With such an exhaust gas aftertreatment system, the risk of an increase in nitrogen oxide tailpipe emissions is reduced by ammonia released in the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides due to high-load operation or regeneration of the particle filter and a new formation of nitrogen oxides by the ammonia slip catalyst.

In a further preferred embodiment of the invention, it is provided that the ammonia barrier catalyst is at least 20 cm, preferably at least 30 cm, particularly preferably at least 40 cm, away from the last exhaust gas aftertreatment component in the direction of flow through the exhaust system for selective, catalytic reduction. By arranging the ammonia blocking catalyst downstream of the last exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides, the exhaust gas temperature in the ammonia blocking catalyst can be lowered compared to the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides, so that the tendency for the formation of new nitrogen oxides by the ammonia Slip catalyst is reduced.

In a preferred embodiment of the exhaust aftertreatment system, it is provided that in the exhaust system, downstream of the first catalytic converter, a particulate filter with a coating for the selective, catalytic reduction of nitrogen oxides and downstream of the particulate filter an SCR catalytic converter are arranged, with downstream of the first catalytic converter and upstream of the particulate filter being a first metering element for metering in reducing agent and downstream of the particle filter and upstream of the SCR catalytic converter a second metering element for metering in reducing agent is arranged, with downstream of the particle filter and upstream of the second metering element an exhaust gas recirculation line of a low-pressure exhaust gas recirculation branching off from the exhaust gas duct of the exhaust system. Such an exhaust gas aftertreatment system enables a particularly efficient exhaust gas aftertreatment of the exhaust gas stream of the internal combustion engine. The nitrogen oxide emissions can be minimized by the two exhaust gas aftertreatment components for selective, catalytic reduction at all operating points of the internal combustion engine. Furthermore, the risk of ammonia being expelled thermally from one of the exhaust gas aftertreatment components can be minimized by a corresponding loading strategy, as a result of which the risk of nitrogen oxide formation from the ammonia is reduced by the ammonia blocking catalytic converter.

• - Durchleiten eines Abgasstroms des Verbrennungsmotors durch den Ammoniak-Sperrkatalysator, wobei
• - das in einem ersten Abgasteilstrom enthaltene Ammoniak (NH3) in einer Oxidationszone des Ammoniak-Sperrkatalysators zu Stickoxiden (NOx) oxidiert wird, wobei
• - das in einem zweiten Abgasteilstrom enthaltene Ammoniak (NH3) die Oxidationszone unverändert durchdringt, wobei
• - sich der erste Abgasteilstrom und der zweite Abgasteilstrom in einem Mischraum miteinander vermischen, und wobei
• - die im Abgasstrom enthaltenen Stickoxiden (NOx) mit dem Ammoniak (NH3) auf dem SCR-Katalysator des Ammoniak-Sperrkatalysators konvertiert werden.

A further partial aspect of the invention relates to a method for the aftertreatment of exhaust gas from an internal combustion engine with at least one combustion chamber, with the internal combustion engine being connected to an exhaust system at its outlet, with a first catalytic converter close to the engine, a Particulate filter and at least one exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides are arranged, wherein downstream of the last exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides, an inventive ammonia blocking catalyst is arranged, comprising the following steps:

• - Passing an exhaust gas flow of the internal combustion engine through the ammonia slip catalyst, wherein
• - The ammonia (NH3) contained in a first partial exhaust gas stream is oxidized in an oxidation zone of the ammonia blocking catalyst to nitrogen oxides (NOx), wherein
• - The ammonia (NH3) contained in a second partial flow of exhaust gas penetrates the oxidation zone unchanged, wherein
• - The first partial flow of exhaust gas and the second partial flow of exhaust gas mix together in a mixing space, and wherein
• - the nitrogen oxides (NOx) contained in the exhaust gas flow are converted with the ammonia (NH3) on the SCR catalytic converter of the ammonia slip catalytic converter.

For exhaust gas aftertreatment, a reducing agent, in particular an aqueous urea solution, is metered into the exhaust gas duct of the internal combustion engine and ammonia is formed from this reducing agent. This ammonia is stored in an exhaust aftertreatment component for the selective, catalytic reduction of nitrogen oxides in order to convert the nitrogen oxides into molecular nitrogen and water vapour. If the temperature of the exhaust aftertreatment component exceeds a threshold temperature of approximately 380°C, the storage capacity for ammonia decreases sharply and the ammonia is released again so that it is introduced into the part of the exhaust aftertreatment system located downstream of the exhaust aftertreatment component. In order to reduce the effects of such a discharge of ammonia from an exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides during high-load operation or regeneration of a particle filter, an ammonia blocking catalyst is provided downstream of the exhaust gas aftertreatment component. At low temperatures, the ammonia that hits the ammonia slip catalyst can be converted into molecular nitrogen and water vapor. This happens, for example, when there is an overdose of reducing agent, ie when more reducing agent is metered into the exhaust gas duct than can be stored in the subsequent exhaust gas aftertreatment components. However, high temperatures in the ammonia blocking catalytic converter cause this ammonia to be oxidized to form nitrogen oxides, so that nitrogen oxides are newly formed on the ammonia blocking catalytic converter. In order to avoid an increase in nitrogen oxide tailpipe emissions, it is provided that in this case only part of the ammonia is oxidized to form nitrogen oxides, so that these nitrogen oxides can be oxidized with the ammonia remaining in the exhaust gas flow in a further SCR catalytic converter to form molecular nitrogen and water vapor. so that this operating condition does not lead to a significant increase in tailpipe emissions.

Unless stated otherwise in the individual case, the various embodiments of the invention mentioned in this application can advantageously be combined with one another.

• 1 einen Verbrennungsmotor mit einem bevorzugten Ausführungsbeispiel für ein erfindungsgemäßes Abgasnachbehandlungssystem;
• 2 ein weiteres Ausführungsbeispiel für einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 3 ein bevorzugtes Ausführungsbeispiel für einen erfindungsgemäßen Ammoniak-Sperrkatalysator;
• 4 ein weiteres bevorzugtes Ausführungsbeispiel für einen erfindungsgemäßen Ammoniak-Sperrkatalysator;
• 5 ein weiteres bevorzugte Ausführungsbeispiel für einen erfindungsgemäßen Ammoniak-Sperrkatalysator;
• 6 ein Ablaufdiagramm zur Durchführung eines erfindungsgemäßen Verfahrens zur Abgasnachbehandlung eines Verbrennungsmotors;
• 7 ein weiteres Ausführungsbeispiel für einen erfindungsgemäßen Ammoniak-Sperrkatalysator;
• 8 ein weiteres Ausführungsbeispiel für einen erfindungsgemäßen Ammoniak-Sperrkatalysator;
• 9 einen Blick auf eine einlassseitige Stirnfläche eines erfindungsgemäßen Ammoniak-Sperrkatalysators;
• 10 ein bevorzugtes Ausführungsbeispiel eines erfindungsgemäßen Ammoniak-Sperrkatalysators, wobei der Ammoniak-Sperrkatalysator als Wickelkatalysator aus zwei metallischen Folien ausgeführt ist; und
• 11 einen Blick auf eine einlassseitige Stirnfläche eines als Wickelkatalysator ausgeführten Ammoniak-Sperrkatalysators.

The invention is explained below in exemplary embodiments with reference to the associated drawings. Show it:

• 1 an internal combustion engine with a preferred embodiment of an exhaust aftertreatment system according to the invention;
• 2 a further exemplary embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention;
• 3 a preferred embodiment of an ammonia slip catalyst according to the invention;
• 4 a further preferred exemplary embodiment of an ammonia slip catalyst according to the invention;
• 5 a further preferred exemplary embodiment of an ammonia barrier catalyst according to the invention;
• 6 a flowchart for carrying out a method according to the invention for the exhaust gas aftertreatment of an internal combustion engine;
• 7 a further exemplary embodiment of an ammonia slip catalyst according to the invention;
• 8th a further exemplary embodiment of an ammonia slip catalyst according to the invention;
• 9 a view of an inlet-side end face of an ammonia slip catalyst according to the invention;
• 10 a preferred embodiment of an ammonia barrier catalyst according to the invention, wherein the ammonia barrier catalyst is designed as a wound catalyst made of two metallic foils; and
• 11 a view of an inlet-side end face of an ammonia barrier catalyst designed as a wound catalyst.

1 shows an internal combustion engine 10 whose outlet 16 is connected to an exhaust system 22 of an exhaust gas aftertreatment system 20 of the internal combustion engine 10 . The internal combustion engine 10 is designed as a self-igniting compression engine based on the diesel principle. Internal combustion engine 10 has a plurality of combustion chambers 12 in which a fuel-air mixture is burned. For this purpose, a fuel injector 14 is provided on each of the combustion chambers 12 in order to inject fuel into the combustion chambers 12 .

The internal combustion engine 10 is preferably embodied as an internal combustion engine 10 charged by means of an exhaust gas turbocharger 18 , a turbine 26 of the exhaust gas turbocharger 18 being arranged downstream of the outlet 16 and upstream of the first emission-reducing exhaust gas aftertreatment component 28 . The internal combustion engine 10 is connected to an engine control unit 100, via which, among other things, the injection quantity and the injection time of the fuel into the combustion chambers 12 are controlled.

The exhaust system 22 includes an exhaust gas duct 24 in which, in the flow direction of an exhaust gas through the exhaust gas duct 24, downstream of the turbine 26 of the exhaust gas turbocharger 18, a first catalytic converter 28 close to the engine is arranged as the first exhaust gas aftertreatment component. The first catalytic converter 28 is preferably designed as an oxidation catalytic converter 30 or as a NOx storage catalytic converter 32 . A particulate filter 34 with a coating 36 for the selective, catalytic reduction of nitrogen oxides and downstream of the particulate filter 34, 36 an SCR catalytic converter 38 are arranged downstream of the first catalytic converter 28 close to the engine.

An ammonia slip catalytic converter 40 is arranged downstream of the SCR catalytic converter 38 in order to prevent the escape of ammonia from a tailpipe of the exhaust system 22 . The ammonia slip catalyst 40 is spaced from the SCR catalyst by at least 20 cm such that the exhaust stream entering the ammonia slip catalyst 40 is cooler than exiting the SCR catalyst 38 . A first metering element 50 for metering a reducing agent, in particular an aqueous urea solution, into the exhaust gas duct 24 of the exhaust system 22 is provided downstream of the first catalytic converter 28 close to the engine and upstream of the particle filter 34 . A first exhaust gas mixer 52 is connected downstream of the first dosing element 50 in order to achieve improved equal distribution between the exhaust gas flow and the metered-in reducing agent before entry into the particle filter 34 with the SCR coating 36 . Downstream of particulate filter 34, an exhaust gas recirculation line 76 of a low-pressure exhaust gas recirculation system 70 branches off at a junction 66 from exhaust gas duct 24 of exhaust gas system 22, which connects exhaust gas system 22 to an intake duct, not shown, upstream of a compressor of exhaust gas turbocharger 18. An exhaust gas recirculation valve 74 and an exhaust gas recirculation cooler 72 are arranged in the exhaust gas recirculation line 76 .

An exhaust gas flap 68 is arranged in the exhaust gas duct 24 downstream of the junction 66, with which the exhaust gas duct 24 can be at least partially blocked and the exhaust gas back pressure in the exhaust gas duct 24 is thus increased in order to control the quantity of exhaust gas recirculated via the low-pressure exhaust gas recirculation system 70.

A second dosing element 54 is provided downstream of the branch 66 and upstream of the SCR catalytic converter 38, which is followed by a second exhaust gas mixer 56 in order to achieve improved uniform distribution between the exhaust gas flow and the metered-in reducing agent before entering the SCR catalytic converter 38.

A differential pressure sensor 62 is arranged upstream and downstream of the particle filter 34 in order to determine the pressure difference across the particle filter 34 and thus to estimate the loading of the particle filter 34 . Furthermore, at least one temperature sensor 60 is provided in the exhaust system 22 in order to detect the exhaust gas temperature of the exhaust gas stream of the internal combustion engine 10 . A NOx sensor 64 is provided downstream of the particulate filter 34 with the SCR coating 36 in order to monitor the effect of the exhaust aftertreatment component with regard to the reduction of nitrogen oxides. A further NOx sensor 64 can be arranged downstream of the SCR catalytic converter 38 and upstream of the ammonia blocking catalytic converter 40 in order to determine the nitrogen oxide concentration downstream of the SCR catalytic converter 38 and thus to check the effect of the exhaust gas aftertreatment system 20 .

The ammonia slip catalyst 40 can have a coolant connection 92 and a coolant return 94 for connection to a coolant circuit run 90 of the internal combustion engine 10 have. The coolant circuit 90 has at least one coolant pump 98 with which the coolant is conveyed through the coolant circuit 90 . The coolant circuit 90 also has at least one cooler 96 with which the temperature of the coolant in the coolant circuit 90 can be reduced.

In 2 a simplified exemplary embodiment of an internal combustion engine 10 with an exhaust gas aftertreatment system 20 according to the invention is shown. The exhaust system 22 of the exhaust gas aftertreatment system comprises an exhaust gas duct 24 in which a first catalytic converter 28 close to the engine is arranged as the first exhaust gas aftertreatment component in the flow direction of an exhaust gas through the exhaust gas duct 24 . The first catalytic converter 28 is preferably designed as an oxidation catalytic converter 30 or as a NOx storage catalytic converter 32 . A particulate filter 34 and an SCR catalytic converter 38 are arranged downstream of the first catalytic converter 28 close to the engine. The particle filter 34 and the SCR catalytic converter 38 can also be combined in one component, in which case the particle filter 34 is designed with a coating 36 for the selective, catalytic reduction of nitrogen oxides (SCR coating). An ammonia blocking catalytic converter 40 is arranged downstream of the SCR catalytic converter 38 or the particle filter 34 with the SCR coating 36 .

In 3 A preferred embodiment of an ammonia slip catalyst 40 is shown. The ammonia slip catalytic converter 40 has a housing 48 in which an oxidation zone 42, a mixing chamber 86 and an SCR catalytic converter 46 are arranged or formed in the direction of flow of an exhaust gas flow through the housing 48 . The ammonia barrier catalyst 40 has a double, perforated wrapping film 78, 88, 102. The double, perforated wrapping film 78, 88, 102 forms a plurality of first channels 80 and second channels 82, which run parallel to one another. By coating the wrapping film 78 on one side with a noble metal coating 84 in an inlet-side section of the ammonia blocking catalytic converter 40, the first channels 80 are set up to oxidize ammonia into a nitrogen oxide. The second channels 82 are uncoated so that the ammonia penetrates the second channels 82 . Gas exchange between the two channels 80, 82 is possible through the holes in the perforated wrapping film 102, so that a mixing space 86 is formed. An outlet-side section of the ammonia slip catalyst 40 is provided with an SCR coating 104 , with both the first channels 80 and the second channels 82 preferably being provided with an SCR coating 104 in this outlet-side section. On the outlet-side portion of the ammonia slip catalyst 40, the nitrogen oxides are reacted with the ammonia and converted into molecular nitrogen and water vapor.

In 4 An alternative exemplary embodiment of an ammonia slip catalyst 40 according to the invention is shown. The ammonia barrier catalytic converter 40 has a first monolith 106 and a second monolith 108 which are spaced apart from one another by a mixing space 86 . The first monolith 106 forms an oxidation zone 42 for the ammonia. For this purpose, a plurality of first channels 80 and second channels 82 running parallel to the first channels 80 are provided in the first monolith 106, the ratio of the first channels 80 to the second channels 82 preferably being approximately 1:1. The first channels 80 are provided with a precious metal plating 84, preferably platinum, palladium or rhodium plating, to convert the ammonia entering the first channels 80. In the process, nitrogen oxides are formed in the channels 80. The second channels 82 are uncoated and allow the ammonia to flow through without conversion. The ammonia and the nitrogen oxides are mixed in the mixing chamber 86, and an exhaust gas mixer 58 can be provided in the mixing chamber 86 for improved mixing. The second monolith 108 has a coating 104 for the selective, catalytic reduction of nitrogen oxides and forms an SCR catalytic converter 44 in the form of an SCR disk 46 . On the second monolith 108, the nitrogen oxides are converted to molecular nitrogen and water vapor by the ammonia.

5 shows another embodiment of an ammonia blocking catalyst 40. In a structure as to 3 or 4 executed, a heat exchanger 110 is additionally integrated into the housing 48 of the ammonia blocking catalytic converter 40 in this exemplary embodiment, which has a coolant connection 92 for connection to a coolant circuit 90 of the internal combustion engine 10 . As a result, the temperature in the ammonia slip catalyst 40 can be reduced, which reduces the formation of nitrogen oxides in the oxidation zone 42 of the ammonia slip catalyst 40 .

In 6 a flowchart for carrying out a method according to the invention for the exhaust gas aftertreatment of an internal combustion engine 10 is shown. Internal combustion engine 10 has at least one combustion chamber 12 and is connected to an exhaust system 22 by its outlet 16 . In the exhaust system 22 are in the direction of flow of an exhaust gas stream of the internal combustion engine 10 through the exhaust system 22, a first catalytic converter 28 close to the engine, in particular an oxidation catalytic converter 30 or a NOx storage catalytic converter 32, a particle filter 34 and at least one exhaust gas aftertreatment component 36, 38 for the selective, catalytic reduction of nitrogen oxides. An ammonia blocking catalyst 40 is arranged downstream of the last exhaust gas aftertreatment component 36, 38 for the selective, catalytic reduction of nitrogen oxides. In a method step <100>, an exhaust gas flow from the internal combustion engine 10 is passed through the ammonia blocking catalytic converter 40 . In a method step <110>, the ammonia contained in a first partial flow of exhaust gas is oxidized in an oxidation zone 42 of the ammonia blocking catalytic converter 40 to form nitrogen oxides (NOx). In a method step <120>, the ammonia contained in a second exhaust gas partial flow is passed through the oxidation zone 42, with the ammonia penetrating the oxidation zone 42 unchanged. In a method step <130>, the first partial flow of exhaust gas and the second partial flow of exhaust gas mix with one another in a mixing space 86 . In a subsequent method step <140>, the nitrogen oxides contained in the first partial exhaust gas stream are converted into molecular nitrogen (N2) and water vapor (H2O) with the ammonia contained in the second partial exhaust gas stream on the SCR catalytic converter 44 of the ammonia blocking catalytic converter 40 .

In 7 Another embodiment of an ammonia slip catalyst 40 is shown. The ammonia slip catalytic converter 40 has a housing 48 in which an oxidation zone 42, a mixing chamber 86 and an SCR catalytic converter 46 are arranged or formed in the direction of flow of an exhaust gas flow through the housing 48 . The ammonia barrier catalytic converter 40 has a plurality of first channels 80 and second channels 82 which run parallel to one another. In this case, the walls of the first channels 80 are provided with a noble metal coating 84 and are set up to oxidize ammonia into a nitrogen oxide. The second channels 82 are uncoated so that the ammonia penetrates the second channels 82 . The mixing space 86 is designed as a free mixing space without additional flow-influencing installations. The alternating arrangement of first channels 80 and second channels 82 enables gas exchange in the mixing chamber 86 . An outlet-side section of the ammonia slip catalyst 40 is provided with an SCR coating 104 , with both the first channels 80 and the second channels 82 preferably being provided with an SCR coating 104 in this outlet-side section. On the outlet-side portion of the ammonia slip catalyst 40, the nitrogen oxides are reacted with the ammonia and converted into molecular nitrogen and water vapor.

In 8th Another embodiment of an ammonia slip catalyst 40 is shown. With essentially the same structure as to 7 embodied, this ammonia blocking catalytic converter 40 has a constriction 112 in the area of the mixing chamber 86 in order to achieve improved mixing of the nitrogen oxides and the ammonia before they enter the SCR catalytic converter 46 .

9 shows an inlet-side end face 114 of an ammonia blocking catalytic converter 40 according to the invention, with the ammonia blocking catalytic converter 40 being designed as a ceramic catalytic converter 116 . The ammonia slip catalytic converter 40 has a multiplicity of first channels 80 and second channels 82 which are arranged alternately in the manner of a checkerboard pattern.

10 shows a preferred embodiment of an ammonia blocking catalyst 40 according to the invention, wherein the ammonia blocking catalyst 40 is designed as a metallic wound catalyst 118 made of two metallic foils 78, 88. The metallic foils 78, 88 form first channels 80 and second channels 82. The metallic wound catalytic converter 118 can be made of two metallic foils 78, 88 which are only coated on one side. The foils 78 , 88 are wound in such a way that the coating on one foil 78 rests against the coating on the other foil 88 . Alternatively, it is possible for one film 78 to be coated on both sides and for the other film 88 to be uncoated.

In 11 an inlet-side end face 114 of such a metallic wound catalytic converter 118 is shown. First channels 80 and second channels 82 are formed through the first foil 78 and the second foil 88 or the intermediate spaces, the first channels 80 being provided with a precious metal coating 84 and the second channels 82 being embodied without a coating.

Reference List

10

combustion engine

12

combustion chamber

14

fuel injector

16

outlet

18

exhaust gas turbocharger

20

exhaust aftertreatment system

22

exhaust system

24

exhaust duct

26

turbine

28

first catalyst

30

oxidation catalyst

32

NOx storage catalyst

34

particle filter

36

SCR coating

38

SCR catalytic converter

40

Ammonia Slip Catalyst

42

oxidation zone

44

SCR catalytic converter

46

SCR disk

48

Housing

50

first dosing element

52

first exhaust mixer

54

second dosing element

56

second exhaust mixer

58

third exhaust mixer

60

temperature sensor

62

differential pressure sensors

64

NOx sensor

66

branch

68

exhaust flap

70

Low-pressure exhaust gas recirculation

72

exhaust gas recirculation cooler

74

exhaust gas recirculation valve

76

exhaust gas recirculation line

78

first wrapping film

80

first channel

82

second channel

84

precious metal coating

86

mixing room

88

second wrapping film

90

coolant circuit

92

coolant connection

94

coolant return

96

cooler

98

coolant pump

100

control unit

102

perforated wrapping film

104

SCR coating

106

first monolith

108

second monolith

110

heat exchanger

112

constriction

114

face

116

ceramic catalyst

118

metal catalyst

Claims (15)

Ammonia blocking catalytic converter (40) for arrangement in an exhaust system (22) of an internal combustion engine (10), comprising an oxidation zone (42) for oxidizing ammonia, a mixing space (86) for mixing ammonia and an oxidation product of the ammonia and, in the direction of flow of the Oxidation zone (42) and the mixing space (86) downstream SCR catalyst (44). Ammonia barrier catalyst (40) after claim 1 , characterized in that the oxidation zone (42), the mixing chamber (86) and the downstream SCR catalytic converter (44) are arranged in a common housing (48). Ammonia barrier catalyst (40) after claim 1 or 2 , characterized in that the SCR catalytic converter (44) is designed as an SCR disc (46). Ammonia barrier catalyst (40) according to one of Claims 1 until 3 , characterized in that the oxidation zone (42) has a plurality of first channels (80) and a plurality of second channels (82), the first channels (80) being provided with a precious metal coating (84) and the second channels (82 ) are uncoated or the second channels (82) are provided with a precious metal coating (84) and the first channels (80) are uncoated. Ammonia barrier catalyst (40) after claim 4 , characterized in that the first channels (80) and the second channels (82) are substantially parallel to each other. Ammonia barrier catalyst (40) according to one of Claims 4 or 5 , characterized in that the ammonia barrier catalytic converter (40) is designed as a double wrapping film (78, 88) at least in the region of the oxidation zone (42), the two wrapping films (78, 88) enclosing the first channels (80) and the second channels (82) train. Ammonia barrier catalyst (40) after claim 6 , characterized in that the double wrapping foil (78, 88) is designed as a perforated wrapping foil (102) which has a gas outlet Exchange between the first channels (80) and the second channels (82) allows. Ammonia barrier catalyst (40) according to one of Claims 6 or 7 , characterized in that the region of the double wrapping foil (78, 88) lying downstream of the oxidation zone (42) in the direction of flow is provided with an SCR coating (104) and forms the SCR catalytic converter (44). Ammonia barrier catalyst (40) according to one of Claims 4 until 7 , characterized in that the first channels (80) and the second channels (82) in the mixing space (86) open, wherein the mixing space (86) promotes mixing of the oxidation product with the ammonia. Ammonia barrier catalyst (40) after claim 9 , characterized in that an exhaust gas mixer (58) is arranged in the mixing chamber (86). Ammonia barrier catalyst (40) according to one of claims 2 until 10 , characterized in that a coolant connection (92) for a coolant circuit (90) of the internal combustion engine (10) is formed on the housing (48) and the coolant of the internal combustion engine (10) flows through the housing (48). Exhaust gas aftertreatment system (20) for an internal combustion engine (10), comprising an exhaust system (22) with an exhaust gas duct (24), in which in the direction of flow of an exhaust gas stream of the internal combustion engine (10) through the exhaust gas duct (24) is a first catalytic converter (28) close to the engine Particulate filter (34) and at least one exhaust gas aftertreatment component (36, 38) for the selective, catalytic reduction of nitrogen oxides are arranged, wherein downstream of the last exhaust gas aftertreatment component (36, 38) for the selective, catalytic reduction of nitrogen oxides, an ammonia blocking catalyst (40) according to one of the Claims 1 until 11 is arranged. Exhaust aftertreatment system (20) after claim 12 , characterized in that the ammonia barrier catalyst (40) from the flow direction through the exhaust system (22) last exhaust gas aftertreatment component for selective catalytic reduction (36, 38) is at least 20 cm away. Exhaust aftertreatment system (20) according to one of Claims 12 or 13 , characterized in that in the exhaust system (22) downstream of the first catalytic converter (28) a particle filter (34) with a coating (36) for the selective, catalytic reduction of nitrogen oxides and downstream of the particle filter (34, 36) an SCR catalytic converter ( 38) are arranged, downstream of the first catalytic converter (28) and upstream of the particle filter (34, 36) a first metering element (50) for metering in reducing agent and downstream of the particle filter (34, 36) and upstream of the SCR catalytic converter (38) a second metering element (54) for metering in reducing agent is arranged, with an exhaust gas recirculation line (76) of a low-pressure exhaust gas recirculation (70) from the exhaust gas duct (24) of the exhaust system downstream of the particle filter (34, 36) and upstream of the second metering element (54). (22) branches off. Method for exhaust gas aftertreatment of an internal combustion engine (10) with at least one combustion chamber (12), the internal combustion engine (10) having its outlet (16) connected to an exhaust system (22), the exhaust system (22) being in the direction of flow of an exhaust gas flow from the internal combustion engine (10) a first catalytic converter (28) close to the engine, a particle filter (34) and at least one exhaust gas aftertreatment component (36, 38) for the selective, catalytic reduction of nitrogen oxides are arranged through an exhaust gas duct (24) of the exhaust system (22), with downstream of the last Exhaust aftertreatment component (36, 38) for the selective, catalytic reduction of nitrogen oxides, an ammonia blocking catalyst (40) according to one of Claims 1 until 11 is arranged, comprising the following steps: - passing an exhaust gas stream of the internal combustion engine (10) through the ammonia slip catalyst (40), wherein - the ammonia (NH3) contained in a first exhaust gas partial stream in an oxidation zone (42) of the ammonia slip catalyst (40) is oxidized to form nitrogen oxides (NOx), wherein - the ammonia (NH3) contained in a second partial exhaust gas flow penetrates the oxidation zone (42) unchanged, wherein - the first partial exhaust gas flow and the second partial exhaust gas flow mix with one another in a mixing chamber (86), and wherein - the nitrogen oxides (NOx) contained in the exhaust gas flow are converted with the ammonia (NH3) on the SCR catalytic converter (44) of the ammonia blocking catalytic converter (40).

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