DE102018101929A1 - Device and method for exhaust aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust aftertreatment system (20) for an internal combustion engine (10), in particular a diesel engine. The exhaust aftertreatment system (20) comprises an exhaust system (22) in which a close-coupled NO storage catalyst (40) or an oxidation catalyst (38) is arranged. Downstream of this first close-coupled catalyst (38, 40), two SCR catalysts (26, 30) are arranged, which are each assigned a metering valve (32, 34) for metering in a reducing agent (92). In this case, the NO storage catalytic converter (40) or the oxidation catalytic converter (38) has an electrical heating element (36) with which the catalytic converter (38, 40) can be heated independently of the exhaust gas flow of the internal combustion engine (10) NO storage catalytic converter (40) or the close-coupled oxidation catalyst (38) from the engine start of the internal combustion engine (10) are electrically heated to reach an operating temperature as quickly as possible, in which a conversion or caching of emissions is possible. Thus, the cold start emissions of the internal combustion engine (10) can be improved.

Description

The invention relates to a device for exhaust aftertreatment of an internal combustion engine and to a method for the exhaust aftertreatment of an internal combustion engine according to the preamble of the independent claims.

The current and increasingly stringent future exhaust gas legislation places high demands on the engine raw emissions and the exhaust aftertreatment of internal combustion engines. The demands for a further reduction in consumption and the further tightening of emission standards with regard to permissible nitrogen oxide emissions pose a challenge to engine developers. In gasoline engines, exhaust gas purification takes place in a known manner via a three-way catalytic converter, as well as the three-way catalytic converter. Catalyst upstream and downstream further catalysts. For diesel engines exhaust gas aftertreatment systems are currently used, which have an oxidation catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst) and a particle filter for the separation of soot particles and optionally other catalysts. In order to bring the catalysts to an operating temperature after a cold start of the internal combustion engine, it is desirable to arrange the catalytic converters as closely as possible to the engine. However, this is not always possible because the space is limited. Therefore, SCR catalytic converters and / or soot particle filters are often arranged in a motor vehicle underbody layer of a motor vehicle. Furthermore, so-called NO _X storage catalytic converters are used for the purification of exhaust gas in order to absorb the nitrogen oxides formed during the combustion of the fuel-air mixture in the combustion chambers of the internal combustion engine. However, these NO _x storage catalysts must be regenerated periodically by a stoichiometric operation, resulting in increased fuel consumption. Another disadvantage of NO _x storage catalysts is that at high exhaust gas temperatures no nitrogen oxides can be stored in the NO _x storage catalytic converter. In addition, NO _x storage catalysts are susceptible to aging, so that the storage capacity decreases significantly with the lifetime of the NO _x storage catalytic converter. To compensate for the tendency to age large catalyst volumes and correspondingly high amounts of noble metals are necessary, which brings with it corresponding disadvantages in terms of space requirements and costs.

Catalysts for the selective catalytic reduction of nitrogen oxides, which are referred to below as SCR catalysts, have the disadvantage that a noticeable conversion of nitrogen oxides only begins at a temperature of about 170 ° C. The ammonia used to reduce the nitrogen oxides, which is usually obtained from an aqueous urea solution, oxidized at temperatures above 450 ° C, so above this temperature also only a small conversion of harmful nitrogen oxides by means of the SCR catalyst is possible. In addition, there is the risk in engines with a low-pressure exhaust gas recirculation that the reducing agent enters the exhaust gas recirculation, where it attaches at low temperatures on the walls of the exhaust passage. In this case, the urea crystallizes out of the aqueous urea solution, which can lead to deposits on the walls of the exhaust gas channel of the low-pressure exhaust gas recirculation, which can limit the function of the exhaust gas recirculation.

More and more efficient internal combustion engines lead to ever lower exhaust gas temperatures in the exhaust system of the internal combustion engine. At the same time, with the introduction of new emission standards, the legislator demands compliance with strict limits under real driving conditions. This makes the conditions for the exhaust aftertreatment more difficult. The challenge is to cover both the low-temperature range, in particular after a cold start of the internal combustion engine, and the high-temperature range, in particular in a high-load operation or in the regeneration of a particulate filter, by combining different components of the exhaust gas aftertreatment.

From the DE 10 2016 223 558 A1 an exhaust aftertreatment system for an internal combustion engine is known, in which in the exhaust system downstream of a turbine of an exhaust gas turbocharger, an oxidation catalyst or a NO _x storage catalyst is arranged. Further downstream, a first metering element for metering in a reducing agent for the selective, catalytic reduction of nitrogen oxides is arranged, which is followed by a first SCR catalyst or a particle filter with a coating for the selective, catalytic reduction of nitrogen oxides. Further downstream, a second metering element for metering in a reducing agent is arranged in the exhaust system, which is followed by a second SCR catalyst downstream.

From the DE 10 2014 105 043 A1 An exhaust aftertreatment system for an internal combustion engine is known. The exhaust aftertreatment system has a first injection device, with which fuel and a second injection device, with which an aqueous urea solution can be metered into the exhaust passage. In this case, downstream of the first injection device, a catalyst for selective catalytic reduction by means of hydrocarbons and an oxidation catalyst and downstream of the second Injector arranged an SCR catalyst and a particulate filter. The catalyst for selective catalytic reduction by means of hydrocarbons is assigned a heating element with which this catalyst can be heated.

A disadvantage of the exhaust aftertreatment systems known from the prior art is that they do not allow optimal conversion of pollutant emissions, in particular NO _x emissions, at all times of operation and not under all operating conditions.

The invention is based on the object to enable a highly efficient exhaust aftertreatment in all temperature ranges and in particular to further reduce the cold-start emissions, in particular the NO _x emissions in the cold start phase.

According to the invention, this object is achieved by an exhaust aftertreatment system for an internal combustion engine with an exhaust system in which in the flow direction of an exhaust gas through the exhaust system a close-coupled first catalyst, downstream of this near-engine first catalyst, a first SCR catalyst and further downstream, a second SCR catalyst are arranged solved , In this case, a first metering module and the second SCR catalyst a second metering module for metering a reducing agent are assigned to the first SCR catalyst in the exhaust system. The close-coupled first catalytic converter and / or at least one of the SCR catalytic converters have an electrical heating element with which at least one of the catalytic converters can be heated independently of the exhaust gas flow of the internal combustion engine. In this case, a position close to the engine is understood to mean a position in the exhaust system with a mean exhaust gas flow path of at most 80 cm, in particular of at most 50 cm, after the outlet of the internal combustion engine. An engine-remote position is found in particular in an underfloor position of a motor vehicle and has a mean exhaust flow path of at least 80 cm, preferably at least 100 cm after the outlet of the internal combustion engine. By two different SCR catalysts, which are arranged at different distances to the outlet of the internal combustion engine, prevail at both SCR catalysts different temperatures. Thus, it is possible to operate at least one of the SCR catalysts in a temperature window to allow an efficient reduction of nitrogen oxides. By means of a corresponding heating element, the engine-near first catalytic converter or one of the SCR catalytic converters can be heated independently of the exhaust gas flow of the internal combustion engine and thus brought to their operating temperature promptly after a cold start of the internal combustion engine, whereby the cold start emissions can be reduced. Thus, it is possible by a combination of several SCR catalysts and an electric heating element to achieve an efficient conversion of pollutants in all operating situations of the internal combustion engine.

By the features listed in the dependent claims advantageous improvements and developments of the exhaust gas aftertreatment system given in the independent claim are possible.

In a preferred embodiment of the invention, it is provided that the first catalytic converter close to the catalyst is designed as an oxidation catalyst, NO _x storage catalytic converter or passive NO _x adsorber. A NO _x storage catalyst or a passive NO _x adsorber has the advantage that nitrogen oxides can be retained in the exhaust gas of the internal combustion engine as long as the SCR catalysts have not yet reached their operating temperature and an efficient conversion of these nitrogen oxide emissions by at least one of the SCR -Catalysts is possible. As a result, the nitrogen oxide emissions in the cold start phase can be reduced.

It is particularly preferred if the close-coupled first catalyst has a heating element in the form of a heating disk, which is connected to the catalytically active structure of the first catalyst. A heating disk can be easily integrated into a catalyst, wherein a simple connection between the heating disk and the catalyst body, for example by a pin connection, is possible.

According to an advantageous embodiment of the invention, it is provided that the first catalytic converter close to the catalyst is designed as a passive NO _x adsorber, wherein the heating element is arranged on the output side of the NO _x adsorber. Since a passive NO _x absorber allows storage of nitrogen oxides at comparatively low temperatures and releases them again at higher temperatures, it is advantageous to arrange the heating element on the output side of the passive NO _x adsorber to the exhaust gas stream downstream of the passive NO _x adsorber to heat up and thus bring the SCR catalyst as soon as possible to its operating temperature.

In a preferred embodiment of the exhaust aftertreatment system, it is provided that the first SCR catalytic converter is designed as a particle filter with a coating for the selective, catalytic reduction of nitrogen oxides. Thereby, an additional particulate filter can be avoided, whereby the exhaust aftertreatment system as a whole can be made more compact and cheaper.

It is particularly preferred if the particle filter has an electric heating disk or a directly heatable substrate. An electric heating disk or a directly heatable substrate allows the particle filter to be brought to its operating temperature more quickly. Further, the heating disk or the heatable substrate can be used to assist in heating the particulate filter to a regeneration temperature, whereby operating phases in which the internal combustion engine is operated to heat the particulate filter with a low efficiency can be reduced.

In a further preferred embodiment of the invention, it is provided that the particle filter comprises an SCR catalyst disk, which is connected upstream of the filter body of the particulate filter. The SCR catalyst disk is thermally isolated from the particulate filter with the SCR coating. The SCR catalyst disk is preferably disposed in the same housing as the particulate filter with the SCR coating but disposed upstream of the particulate filter. This SCR catalyst disk is comparatively small in volume, so that this SCR catalyst disk heats up quickly and comparatively quickly reaches the temperature window for the selective, catalytic reduction of nitrogen oxides. In addition, the SCR catalytic converter disk has a higher washcoat quantity per area than the coated particle filter and, due to the higher washcoat amount, has a better volume per volume conversion performance than the SCR coating particle filter.

In a further improvement of the invention, it is provided that the second SCR catalyst comprises an ammonia blocking catalyst, which is connected downstream of the catalyst body of the SCR catalyst. This can prevent that in the selective, catalytic reduction of nitrogen oxides not converted in the SCR catalyst ammonia is emitted as a tailpipe emission. As a result, the emissions of the internal combustion engine can be further reduced.

According to the invention, a method for exhaust aftertreatment of an internal combustion engine with an exhaust aftertreatment system according to the invention is proposed, wherein the engine-near first catalyst and / or one of the SCR catalysts are heated starting from an engine start of the internal combustion engine. This ensures that the catalytic converters can reach their operating temperature faster than exclusive heating by the exhaust gas flow of the internal combustion engine and thus that the cold start emissions can be reduced.

In an advantageous embodiment of the method, it is provided that the close-coupled, first catalyst is designed as an electrically heatable NO _X storage catalytic converter, wherein the NO _x storage catalytic converter is electrically heated until the NO _x storage catalytic converter has reached a threshold temperature, starting from an efficient intermediate storage of nitrogen oxides in the NO _x storage catalytic converter is possible. NO _X storage catalysts can store nitrogen oxides from a temperature of about 100 ° C. For example, an SCR catalytic converter reaches a temperature window in a temperature range between 200 ° C and 450 ° C in which an efficient conversion of nitrogen oxide emissions is possible. In order to reduce emissions in the cold start phase, it is therefore necessary to bring the NO _x storage catalytic converter to its operating temperature as soon as possible after the cold start. The storage volume of the NO _x storage catalytic converter should be selected so that the time window can be bridged until at least one of the SCR catalysts has reached its operating temperature.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 2 ein erfindungsgemäßes Abgasnachbehandlungssystem für einen Verbrennungsmotor;
• 3 verschiedene Positionen für ein Heizelement an einem motornahen ersten Katalysator;
• 4 mögliche Konfigurationen zur Beheizung eines Partikelfilters mit einer Beschichtung zur selektiven, katalytischen Reduktion von Stickoxiden in einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 5 einen Partikelfilter mit einer SCR-Beschichtung, dem eine SCR-Katalysatorscheibe vorgeschaltet ist; und
• 6 einen SCR-Katalysator eines erfindungsgemäßen Abgasnachbehandlungssystems, dem ein Ammoniak-Sperrkatalysator nachgeschaltet ist.

The invention will be explained below in embodiments with reference to the accompanying drawings. Identical components or components with the same function are identified by the same reference numerals. Show it:

• 1 an internal combustion engine with an exhaust aftertreatment system according to the invention;
• 2 an exhaust aftertreatment system according to the invention for an internal combustion engine;
• 3 various positions for a heating element on a first catalyst near the engine;
• 4 possible configurations for heating a particulate filter with a coating for the selective, catalytic reduction of nitrogen oxides in an exhaust aftertreatment system according to the invention;
• 5 a particulate filter with an SCR coating, preceded by an SCR catalyst disk; and
• 6 an SCR catalyst of an exhaust aftertreatment system according to the invention, which is followed by an ammonia blocking catalyst.

1 shows an internal combustion engine 10 with an air supply system 70 and an exhaust system 22 , The internal combustion engine 10 has a plurality of combustion chambers 12 on, in which a fuel-air mixture is burned. The internal combustion engine 10 has an inlet 13 on which with the air supply system 70 connected is. The internal combustion engine 10 also has an outlet 16 on, which with the exhaust system 22 connected is. At the internal combustion engine 10 a high pressure exhaust gas recirculation is provided, which is the outlet 16 with the inlet 14 combines. In the high-pressure exhaust gas recirculation EGR valve is arranged, with which the amount of recirculated exhaust gas can be controlled.

The air supply system 70 includes an air filter which is connected to an intake passage 74 is arranged. Downstream of the air filter is a compressor 72 an exhaust gas turbocharger 18 arranged, which compresses the fresh air. Further downstream of the compressor 72 is in the intake channel 74 a charge air cooler 76 provided, which cools the compressed fresh air and thus the filling of the combustion chambers 12 further improved. Downstream of the intercooler 76 A throttle may be placed around the combustion chambers 12 of the internal combustion engine 10 to control the amount of air supplied.

The exhaust system 22 has an exhaust duct 50 in, in the direction of flow of an exhaust gas of the internal combustion engine 10 through the exhaust duct 50 a turbine 28 the exhaust gas turbocharger 18 and downstream of the turbine 28 a plurality of catalysts 24 . 26 30 . 52 is arranged. As the first exhaust aftertreatment component are in the exhaust passage 50 a close-coupled first catalyst 24 , preferably a NO _x storage catalyst 40, a diesel oxidation catalyst 38 or a passive NO _x adsorber 54, which is a near-engine first SCR catalyst 26 , in particular a particle filter 42 with a coating 44 for the selective catalytic reduction of nitrogen oxides, is preceded. Downstream of the turbine 28 and upstream of the first catalyst near the engine 24 , preferably at the entrance of the first catalytic converter close to the engine 24 is an electric heating element 36 for heating the near-engine, first catalyst 24 provided to bring this as soon as possible after a cold start to its operating temperature. Downstream of the first catalyst near the engine 24 and upstream of the particulate filter 42 with the coating 44 for the selective catalytic reduction of nitrogen oxides is a first metering valve 32 for dosing a reducing agent 92 in the exhaust duct 46 arranged. Downstream of the particulate filter 42 there is a branching point 84 , at which a low-pressure exhaust gas recirculation 80 from the exhaust duct 50 the exhaust system 22 branches. Downstream of the branching point 84 is in the exhaust duct 50 an exhaust flap 94 arranged, with which the exhaust duct 50 can be at least partially closed and in this way the low pressure exhaust gas recirculation 80 into the air supply system 70 recycled exhaust gas can be controlled. Downstream of the exhaust flap 94 is on the exhaust duct 50 a second metering valve 34 arranged, with which reducing agent 92 upstream of a second SCR catalyst 30 in the exhaust duct 50 can be metered. At the exhaust duct 50 Furthermore, at least one temperature sensor is arranged to determine an exhaust gas temperature or a component temperature of a component 24 . 26 . 30 to determine the exhaust aftertreatment. Based on this temperature and / or the current operating state of the internal combustion engine 10 can in a control unit 90 then more temperatures in the exhaust duct 50 , in particular the temperatures of the first SCR catalyst 26 and the second SCR catalyst 30 , be calculated. Alternatively, it can also be on each of the SCR catalysts 26 . 30 a temperature sensor may be arranged to match the temperature of the respective SCR catalyst 26 . 30 to investigate.

The low pressure exhaust gas recirculation 80 includes an exhaust gas recirculation passage 82 in which in the flow direction of an exhaust gas through the exhaust gas recirculation passage 82 an exhaust gas recirculation cooler 86 and downstream of the exhaust gas recirculation cooler 86 an exhaust gas recirculation valve 88 for controlling the air supply system 70 supplied amount of exhaust gas are arranged. The exhaust gas recirculation channel 82 rises at the branching point 84 from the exhaust duct 50 and ends at the junction 78 in the intake channel 74 ,

Through the in 1 illustrated exhaust aftertreatment system 20 for an internal combustion engine 10 is a multiple dosage of reducing agent 92 in the exhaust system 22 possible. It is provided, the reducing agent 92 in cold combustion engine 10 close to the engine close to the outlet 16 of the internal combustion engine 10 and with the engine-related first SCR catalyst 26 to convert harmful nitrogen oxides into non-toxic molecular nitrogen and water vapor. Remote engine is the second metering valve 34 arranged in such a way that the exhaust gas temperatures by the distance to the outlet 14 of the internal combustion engine 10 are lower and thus a conversion for medium to high loads of the internal combustion engine 10 is allowed without oxidizing ammonia directly to a high degree.

In 2 is a further illustration of the exhaust aftertreatment system according to the invention 20 shown. Here is the heating element 36 as a heating disk 56 formed, which on the input side the first close-coupled catalyst 24 is arranged. The close-coupled first catalyst 24 is preferably designed as a NO _x storage catalytic converter 40. Downstream of the first metering valve 32 and upstream of the first SCR catalyst near the engine 26 is in the exhaust system 22 a first exhaust gas mixer 46 arranged. Downstream of the second metering valve 34 and upstream of the second SCR catalyst 30 is a second exhaust gas mixer in the exhaust system 48 arranged. The second SCR catalyst 30 is an ammonia blocking catalyst 52 downstream to prevent in the second SCR catalyst 30 unreacted ammonia enters the environment as a pollutant emission.

Alternatively, the heating disk 56 also like in 3 shown in a center position or output side of the motor near the first catalyst 24 be arranged. Is the heating disk 56 on the output side of the first catalytic converter close to the engine 24 arranged, it may additionally support the evaporation of the reducing agent 92 be used when the first metering valve 32 corresponding to the flow direction of the exhaust gas through the exhaust passage 50 on the heating disk 56 is oriented.

Optional is as in 4 illustrated an additional electrical heating of the particulate filter 42 with the coating 44 intended for the selective, catalytic reduction of nitrogen oxides. The energy can be transferred via a second heating disk 58 , which preferably the input side of the particulate filter 42 is arranged, or via an electrically directly heatable substrate of the particulate filter 42 be introduced. Alternatively, in an electric heating of the particulate filter 42 also an electrical heating of the motor near the first catalyst 24 omitted. The electrical supply of the heating elements 36 is preferably done via a 12 volt, 24 volt or 48 volt electrical system of a motor vehicle.

In 5 is another embodiment of the close-coupled first SCR catalyst 30 shown. Here is the SCR catalyst 26 as a particle filter 42 with a coating 44 designed for the selective, catalytic reduction of nitrogen oxides, which on the input side an SCR catalyst disk 62 upstream. Alternatively, in this embodiment, the coating 44 of the particulate filter 42 In this case, the conversion of nitrogen oxide emissions exclusively by the SCR catalyst disc 62 he follows.

In 6 are two embodiments for the second SCR catalyst 30 shown. In this case, the catalytically active structure for the selective, catalytic reduction of nitrogen oxides is in each case an ammonia blocking catalyst 52 downstream. The second SCR catalyst 30 can be both one-piece, as well as in a two-brick variant with a first catalyst element 66 and a second catalyst element 68 be executed. In this case, the first catalyst element 66 as a pure SCR catalyst, while the second catalyst element 68 as ammonia blocking catalyst 52 or as SCR catalyst with downstream ammonia blocking catalyst 52 is executed. In both cases, a heating of the second SCR catalyst 30 over a third heating disk 64 possible, which in the flow direction of an exhaust gas of the internal combustion engine 10 on the input side of the second SCR catalyst 30 is arranged.

After a cold start of the internal combustion engine 10 First, the close-coupled NO _x storage catalyst 40 is electrically heated to achieve a first threshold temperature T _s1 , from which a storage of nitrogen oxides in the NO _x storage catalyst 40 is possible. This temperature is in known NO _x storage catalysts 40 at about 100 ° C. Alternatively, it is also possible for the NO _x storage catalytic converter before the start of the internal combustion engine 10 electrically to further reduce the time to reach its operating temperature. If the NO _x storage catalytic converter 40 has reached this first threshold _temperature T _s1 , then further heating of the exhaust gas aftertreatment takes place, which is achieved both by the electric heating element 36 as well as the exhaust gas flow of the internal combustion engine 10 he follows. The resulting during combustion nitrogen oxide emissions are stored in the NO _x storage 40. In addition, the other exhaust aftertreatment components, in particular the SCR catalysts 26 . 30 by additional heating disks 58 . 64 be electrically heated. If at least one of the SCR catalysts has reached a light-off temperature, reducing agent is metered in 92 through the respective SCR catalyst 26 . 30 associated dosing. Because the first SCR catalyst is located closer to the engine, it is expected to first reach its operating temperature. Exceeds the exhaust gas temperature a second threshold temperature T _S2 , for example, by a high-load operation or by a regeneration of the particulate filter 42 , so is the first metering valve near the motor 32 on the motor remote second metering valve 34 switched to an oxidation of ammonia and thus reduced performance of the SCR catalyst 26 to avoid. The inventive method, it is possible that in any operating situation, the pollutants of the engine can be effectively reduced, whereby both in a cold start phase and in high load operation, an efficient reduction of nitrogen oxide emissions is possible.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

combustion chamber

14

inlet

16

outlet

18

turbocharger

20

aftertreatment system

22

exhaust system

24

close to the engine, first catalyst

26

first SCR catalyst

28

turbine

30

second SCR catalyst

32

first metering valve

34

second metering valve

36

heating element

38

oxidation catalyst

40

NO _X storage catalyst

42

particulate Filter

44

Coating for the selective, catalytic reduction of nitrogen oxides

46

first exhaust mixer

48

second exhaust mixer

50

exhaust duct

52

Ammonia slip catalyst

54

passive NO _x adsorber

56

heated window

58

second heating disk

60

directly heatable substrate

62

SCR catalyst disk

64

third heating disk

66

first catalyst element

68

second catalyst element

70

intake system

72

compressor

74

intake port

76

Intercooler

78

junction

80

Low-pressure exhaust gas recirculation

82

Exhaust gas recirculation passage

84

branch

86

Exhaust gas recirculation cooler

88

Exhaust gas recirculation valve

90

control unit

92

reducing agent

94

exhaust flap

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102016223558 A1 [0005]
• DE 102014105043 A1 [0006]

Claims (10)

Exhaust gas aftertreatment system (20) for an internal combustion engine (10) with an exhaust system (22), in which in the flow direction of an exhaust gas through the exhaust system (22) a close-coupled first catalyst (24), downstream of this close-coupled first catalyst (24), a first SCR catalyst (26) and further downstream, a second SCR catalyst (30) are arranged, wherein the first SCR catalyst (26) a first metering module (32) and the second SCR catalyst (30) a second metering module (34) for metering a Reductant (92) are associated with the exhaust system (22), characterized in that the close-coupled first catalyst (24) and / or at least one of the SCR catalysts (26, 30) an electric heating element (36, 56, 58, 64) having. Exhaust after-treatment system (20) according to Claim 1 , characterized in that the close-coupled first catalyst (24) as an oxidation catalyst (38), NO _x storage catalyst (40) or passive NO _x adsorber (54) is executed. Exhaust after-treatment system (20) according to Claim 2 , characterized in that the close-coupled first catalyst (24) has a heating element (36) in the form of a heating disk (56), which is connected to the catalytically active structure of the first catalyst (24). Exhaust after-treatment system (20) according to one of Claims 1 to 3 , characterized in that the close-coupled first catalyst (24) is designed as a passive NO _x adsorber (54), wherein the heating element (36) is arranged on the output side of the NO _x adsorber (54). Exhaust after-treatment system (20) according to one of Claims 1 to 4 , characterized in that the first SCR catalyst (26) is designed as a particle filter (42) with a coating (44) for the selective catalytic reduction of nitrogen oxides. Exhaust after-treatment system (20) according to Claim 5 , characterized in that the particle filter (42) has an electric heating disk (58) or a directly electrically heatable substrate (60). Exhaust after-treatment system (20) according to Claim 5 or 6 , characterized in that the particulate filter (42) comprises an SCR catalyst disc (62), which is connected upstream of the filter body of the particulate filter (42). Exhaust after-treatment system (20) according to one of Claims 1 to 7 , characterized in that the second SCR catalyst (30) comprises an ammonia blocking catalyst (52), which is connected downstream of the catalyst body of the SCR catalyst (30). A method for exhaust aftertreatment of an internal combustion engine (10) with an exhaust aftertreatment system (20) according to one of Claims 1 to 8th , characterized in that the close-coupled first catalytic converter (24) and / or one of the SCR catalysts (26, 30) from an engine start of the internal combustion engine (10) are heated. Process for exhaust aftertreatment after Claim 9 , characterized in that the close-coupled, first catalyst (24) is designed as an electrically heatable NO _x storage catalytic converter (40), wherein the NO _x storage catalytic converter (40) is electrically heated until the NO _x storage catalytic converter (40) has reached a threshold temperature (T _s ), from which an efficient intermediate storage of nitrogen oxides in the NO _x storage catalytic converter (40) is possible.

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