DE102018200452A1 - Desulfurization of individual nitrogen oxide storage catalysts in a dual nitrogen oxide storage catalyst system - Google Patents

Abstract

A process is provided for desulphurizing individual nitrogen oxide storage catalysts in a nitrogen oxide storage catalyst system having at least one first and at least one second nitrogen oxide storage catalyst in the exhaust gas tract of an internal combustion engine, wherein the nitrogen oxide storage catalysts can be desulfurized independently of one another by conditions necessary for this by immediately upstream of the nitrogen oxide storage catalysts by means of respectively arranged therein Feeder can be provided in the exhaust tract fuel introduced. Furthermore, an arrangement for carrying out the method is provided.

Description

The invention relates to a method for desulfurizing individual nitrogen oxide storage catalysts in a nitrogen oxide storage catalytic converter system in the exhaust gas tract of an internal combustion engine and to an arrangement for carrying out the method.

Nitrogen oxide storage catalysts (also referred to as lean NOx traps, in English lean NOx trap, LNT ) are used for the temporary adsorption and subsequent conversion of nitrogen oxides from the exhaust gas of internal combustion engines. In addition, they fulfill their tasks of oxidative aftertreatment of carbon monoxide (CO) and hydrocarbons (HC). In lean operation of an internal combustion engine, ie an operation with an air / fuel mixture in which air and thus oxygen is present in excess, resulting nitrogen oxides can in one LNT get saved; to oxidized the LNT the nitrogen monoxide (NO) contained in the lean exhaust gas to nitrogen dioxide (NO ₂ ) and then stores it in the form of nitrates. With increasing nitrogen oxide loading of a LNT is increasingly decreasing its storage capacity. Also contained in the exhaust sulfoxides are in LNT saved. Temperature, exhaust gas flow and sulfur loading of one LNT affect its storage capacity.

Is the storage capacity of the LNT exhausted, it must be regenerated. During regeneration, the stored nitrogen oxides are desorbed again and catalytically active components of the LNT reduced to nitrogen with the aid of the rich exhaust gas components (CO, HC); Unreduced nitrogen oxides can also be reduced in a downstream selective catalytic reduction (SCR) catalyst. For the regeneration of a LNT the exhaust gas is enriched, for example by increasing the amount of fuel injection in the engine and / or reducing the supply of fresh air. This creates a substoichiometric ratio of oxygen to fuel. The ratio can also be expressed by a lambda value which is then less than 1. This stoichiometric ratio can also be established by injecting fuel into the exhaust tract. In the foreground, mainly nitrogen oxides are removed, which is why one speaks of a DeNox purge. Also sulfur compounds are released during the purge LNT removed, wherein the removal of sulfur compounds effectively at a temperature of at least 600 ° C works. Desulphurization works below this temperature, but slower. The removal works best in rich operation, but sulfur oxides at that temperature can be removed even in lean operation, but the high temperature must be maintained for longer ( DE 10 2016 203 214 A1 ).

The level of nitrogen oxide emissions is subject to strict legal regulations. Exhaust after-treatment systems with only one LNT Often, the nitrogen oxides contained in the exhaust gas can not be sufficiently converted. One way to make nitrogen oxide conversion more efficient is to arrange a second LNT in the exhaust tract ( KR 1 015 274 B1 ). Also the second LNT must be regenerated and desulphurised. Two arranged in series LNT are in different positions in the exhaust system, which exposes them to different thermal conditions.

Becomes a LNT regenerated in rich operation, the exhaust gas downstream of the LNT for a certain period of time still a stoichiometric value. Changing the lambda value downstream of the LNT in a sub-stoichiometric area is an indication that the regeneration of the LNT is complete. The lambda value approaches downstream of the LNT the upstream of the LNT until the values are equal or nearly equal. This phenomenon is also referred to as lambda breakthrough.

In an exhaust aftertreatment device having two in series LNT Delays the regeneration of the first LNT the possibility of regeneration of the downstream second LNT because downstream from the first LNT no sub-stoichiometric ratios exist, as long as the first LNT was not completely regenerated, ie no lambda breakthrough occurred. Therefore, the two must LNT conventionally be regenerated sequentially. However, the total time to regenerate such an exhaust aftertreatment device is only one compared to regeneration LNT increases and fuel consumption while regenerating the two LNT increased accordingly. In addition, the regeneration duration also increases the likelihood that the process must be aborted due to unfavorable driving conditions (eg when disengaging or braking). Stick and sulfur oxides are therefore often from the second LNT not as efficiently removed as from the first one.

The provision of substoichiometric exhaust conditions and especially of sufficiently high temperatures for desulfurization is a technical challenge. It is the task of desulfurizing two arranged in series LNT more efficient compared to conventional methods.

• - Bereitstellen einer für ein Entschwefeln ausreichenden Temperatur in mindestens einem der LNT,
• - Bereitstellen von unterstöchiometrischen Abgasbedingungen in dem besagten LNT für eine bestimmte zeitliche Dauer,
• - Bereitstellen von überstöchiometrischen Abgasbedingungen in dem besagten LNT für eine bestimmte zeitliche Dauer,
• - Wechseln der besagten Abgasbedingungen für eine bestimmte Anzahl von Wechseln, wobei die Temperatur des Abgases aufrechterhalten wird,

wobei zum Bereitstellen von unterstöchiometrischen Abgasbedingungen und der besagten Abgastemperatur das besagte Reduktionsmittel mittels der entsprechenden stromaufwärts des besagten LNT angeordneten Zuführeinrichtung eingeleitet wird.A first aspect of the invention relates to a method for controlling a desulfurization of nitrogen oxide storage catalysts in a nitrogen oxide storage catalytic system in the exhaust gas tract of an internal combustion engine of a motor vehicle, wherein the Nitrogen oxide storage catalyst system at least a first LNT and at least one second downstream of the first one in the exhaust gas flow direction LNT , at least a first, downstream of the first LNT arranged and at least a second, upstream of the second LNT arranged supply means suitable for supplying a reducing agent into the exhaust tract, the arrangement comprising at least one further exhaust gas aftertreatment device and at least one temperature measuring device, comprising the steps:

• Providing a sufficient for a desulfurizing temperature in at least one of LNT .
• Providing substoichiometric exhaust conditions in said one LNT for a certain amount of time,
• Providing stoichiometric exhaust conditions in said one LNT for a certain amount of time,
• Changing said exhaust conditions for a certain number of cycles while maintaining the temperature of the exhaust gas,

wherein, for providing substoichiometric exhaust conditions and said exhaust gas temperature, said reductant means via the corresponding upstream of said one LNT arranged feeding device is initiated.

The inventive method allows the two LNT can be independently desulfurized. This is advantageous because overall less fuel is needed compared to conventional methods because sufficiently high exhaust gas temperatures can be provided over a shorter period of time. Furthermore, by the each LNT associated feed advantageously allows that under all driving conditions both LNT the minimum necessary temperature for effective desulfurization is achieved. Also, the desulfurization of the individual LNT advantageously be controlled in dependence on their respective sulfur loading, wherein it can be terminated earlier at a comparatively low sulfur loading than at a higher sulfur loading. For desulphurisation each LNT can be provided exactly the amount of reducing agent needed for desulfurization, which also advantageous fuel is saved. It is clear that the internal combustion engine is in operation for carrying out the method.

The temperature provided for desulfurization is preferably at least 600 ° C. The temperature of at least 600 ° C shall be interpreted as providing a temperature in a range of 600 - 700 ° C. At temperatures lower than 600 ° C, desulphurization is correspondingly slower, but basically works. The inventive method works in this sense, even if 600 ° C can not be achieved. Too high temperatures, however, unfavorably contribute to the premature thermal aging of a LNT at. To provide the locally required temperatures, the introduced reducing agent is burned; the combustion can be initiated, for example, by means of a catalyst arranged in the region of the feed device or by means of an electric igniter arranged there.

Preferably, fuel is used as the reducing agent for the reduction of nitrogen oxides, which can be introduced from the supply device into the exhaust gas tract. The fuel is in particular the same, which is also used as fuel for operating the internal combustion engine. In this case advantageously no additional tank must be provided and refilled periodically, which simplifies the construction and operation of the exhaust aftertreatment device. In this case, it is advantageous to inject atomized fuel in order to effect effective enrichment of the exhaust gas mixture.

In a preferred embodiment of the method, the first LNT and the second LNT Desulfurized simultaneously, with desulphurization of the first LNT Reducing agent on the first feeder and for desulfurizing the second LNT Reducing agent is introduced via the second feeder in the exhaust system. In this embodiment, advantageously, the heat of the exhaust gas used to heat the first LNT is needed, in the sense also for heating the second LNT be used, that less reducing agent must be supplied via the second feeder to those for the desulfurization of the second LNT to provide necessary temperature. It is also provided in this embodiment that the desulfurization of the two LNT overlap in time, or very short (1 - 10 s) are performed sequentially, especially the second LNT shortly after the first one LNT Desulfurizes to the high temperatures of the first LNT advantageous for providing high temperatures of the second LNT to use.

The simultaneous desulphurisation of both LNT also has the advantage that when desulfurizing from the first LNT Sulfur compounds released into the exhaust gas are not immediately downstream again in the second LNT be absorbed. If substoichiometric ratios are provided by introducing reducing agent by means of the second supply device, storage of the sulfur compounds in the second is made possible LNT already suppressed. By the method according to the invention already stored sulfur compounds also from the second LNT away.

In a further preferred embodiment of the method, the first LNT and the second LNT Desulfurized at different times, with the desulfurization of the first LNT Reducing agent on the first feeder and desulfurization of the second LNT Reducing agent is introduced via the second feeder in the exhaust system. By way of example, the first LNT be operated regularly, with nitrogen oxides are absorbed from the exhaust gas and it is regenerated when needed, while the second LNT is desulfurized. This may be useful, for example, if the sulfur loading of the second LNT much higher than the first LNT , Advantageously, thereby during a desulfurization of the second LNT maintain control of nitrogen oxide emissions to the environment.

The further, between the first LNT and the second LNT disposed exhaust aftertreatment device is preferably a particulate filter. In this case, the steps for desulfurizing the second are preferably simultaneously with a regeneration of the particulate filter in the method LNT carried out. By introducing the reducing agent via the second feed substoichiometric conditions are in the second LNT provided. The amount of oxygen in the exhaust gas conventionally required for filter regeneration is at least partially already reduced downstream of the filter and, as mentioned, is balanced by introducing reducing agent to provide substoichiometric exhaust conditions. Advantageously, the high exhaust gas temperatures required in the filter generation are utilized, since less energy and therefore fuel is needed to produce the second, downstream of the particulate filter for desulfurizing LNT to provide necessary temperature. The fuel cost is compared to one made after a filter regeneration desulfurization of the second LNT Also advantageous because lower, because the total duration of filter regeneration and desulfurization of the second LNT is shorter.

Preferably, the desulfurization of the first and / or second LNT regularly performed as a function of the operating time of the motor vehicle. In other words, the two LNT preferably desulfurized at regular intervals.

Desulfurization of the first and / or second is also preferred LNT depending on their respective sulfur loading. The current sulfur loading of the individual LNT In this case, it is preferably determined model-based in a manner known to the person skilled in the art. The current sulfur loading of the individual LNT can preferably also be determined on the basis of sensor data. Model and sensor based determination of sulfur loading can also be combined.

A second aspect of the invention relates to an arrangement of an internal combustion engine having an exhaust gas tract in a motor vehicle, wherein in the exhaust gas tract at least a first LNT and at least one in the exhaust gas flow direction downstream of the first LNT arranged second LNT , at least a first, downstream of the first LNT arranged and at least a second, upstream of the second LNT arranged means for supplying a reagent for enriching the exhaust gas to a substoichiometric ratio suitable means, at least one further exhaust gas aftertreatment device and at least one temperature measuring device are arranged, wherein the arrangement comprises a control device which is adapted to control the inventive method. The advantages of the arrangement correspond to the advantages of the method.

A third aspect of the invention relates to a motor vehicle with an inventive arrangement.

• 1 eine schematische Darstellung einer Ausführungsform der erfindungsgemäßen Anordnung.
• 2 ein Flussdiagramm einer Ausführungsform des erfindungsgemäßen Verfahrens.
• 3 ein Zustandsdiagramm einer Ausführungsform des erfindungsgemäßen Verfahren.

The invention will be explained in more detail with reference to FIGS. Show it:

• 1 a schematic representation of an embodiment of the inventive arrangement.
• 2 a flowchart of an embodiment of the method according to the invention.
• 3 a state diagram of an embodiment of the inventive method.

An inventive arrangement 1 In the embodiment shown in FIG 1 an internal combustion engine 2 on. The internal combustion engine 2 is particularly a self-igniting internal combustion engine, but can also be a spark-ignition internal combustion engine. The internal combustion engine 2 is supplied via a not shown intake with charge air and injectors in the intake or directly into the combustion chambers of the internal combustion engine with fuel. For deriving the resulting when burning fuel exhaust gas is the internal combustion engine 2 with an exhaust tract 3 connected.

In the exhaust tract 3 is an LNT system 4 arranged. The LNT system (LNT, lean NOx trap, nitrogen storage catalyst) has a first LNT 5 and a second LNT 6 on, the downstream of the first LNT 5 is arranged. Between the first LNT 5 and the second LNT 6 is a particle filter 7 arranged. Further devices for exhaust gas aftertreatment, for example oxidation catalysts and / or catalysts for selective catalytic reduction and particle filters, may be present in the exhaust gas tract, eg upstream and / or downstream of the LNT system 4 , between the LNT 5 . 6 or with one or both LNTs 5 . 6 be arranged combined in a device.

Immediately upstream of the first LNT 5 is a first feeder 8th for supplying a reducing agent, and immediately upstream of the second LNT 6 a second feeder 9 arranged for supplying a reducing agent. As a reducing agent fuel is used in the embodiment. The feeders 8th . 9 are formed in the embodiment as injectors with which the fuel in the exhaust system 3 can be injected. The fuel can be introduced especially in nebulized form. The amount of fuel supplied is controlled by a controller 10 controlled as in 1 by the control device 10 to the feeders 8th . 9 illustrated by dashed arrows.

In front of the LNT 5 . 6 is each a temperature sensor 11 arranged. There may be other temperature sensors, lambda probes, nitrogen oxide sensors and other measuring devices at different locations of the exhaust gas tract 5 be arranged. Lambda sensors or nitrogen oxide sensors are then particularly immediately upstream and downstream of the LNT 5 . 6 arranged. The sensors are connected to the control device 10 in connection, as by the of the sensors 11 to the control device pointing arrows is illustrated. The temperatures in the LNT 5 . 6 and elsewhere in the exhaust tract, and oxygen and nitrogen oxide concentrations upstream and downstream of the LNT 5 . 6 can additionally or alternatively be determined model-based.

During operation of the internal combustion engine 2 is exhaust gas through the exhaust tract 3 directed. During a lean operation of the internal combustion engine 2 are nitrogen oxides contained in the exhaust gas in the LNT 5 . 6 absorbed. Furthermore, it will be in the LNT 5 . 6 also absorbs sulfur compounds from the exhaust gas. While for the regeneration of LNT 5 . 6 With respect to nitrogen oxide storage capacity, providing substoichiometric exhaust conditions is sufficient, temperatures of at least 600 ° C must be provided to remove the sulfur compounds in addition to alternating rich and lean exhaust conditions.

On LNT must be desulfurized when the sulfur loading LS of LNT a value LSd (d for start of desulfurization = deSOx) exceeds, which corresponds to a predetermined sulfur loading threshold, from which LNT desulfurized. The desulfurization is stopped when the sulfur loading LS of LNT falls below a value LSe (e for the end of desulfurization) corresponding to a predetermined sulfur loading threshold from which desulfurization of the sulfur LNT can be stopped. Ideally equivalent LSe the value above which no sulfur compounds in the LNT are stored.

In one embodiment of the method according to the invention 2 becomes during the current operation of the internal combustion engine in a first step S1 an exhaust gas temperature of at least 600 ° C in at least one of LNT provided, ideally in a temperature window of 600 - 700 ° C. For the purposes of the invention, the temperature is made possible by fuel through the feeders 8th . 9 each immediately upstream of the LNT 5 . 6 is fed into the exhaust tract and burned. So should the first LNT 5 be desulfurized, fuel by means of the feeder 8th supplied, should the second LNT 6 be desulfurized, fuel by means of the second feeder 9 fed. The amount of fuel supplied is determined by the controller as a function of the temperature in the LNT controlled. In this way, the temperature is selectively targeted in the first LNT 5 and / or second LNT 6 increased (whichever LNT or whether both should be desulphurized simultaneously), without other facilities in the exhaust system 3 or the piping of the exhaust tract 3 exposed to high temperatures.

In a second step S2 For a certain period of time, the stoichiometric exhaust conditions in the first LNT are determined 5 and / or LNT 6 provided. This is also done by supplying fuel through the feeders 8th or. 9 , It is clear that at the beginning of the procedure the step S1 and S2 can also be carried out at the same time, since with the supply of fuel to increase the temperature also substoichiometric conditions are created.

In a third step S3 lean exhaust gas is provided by the internal combustion engine 2 is operated with a lean fuel-air mixtures and no additional fuel in the exhaust tract 3 is supplied. The temperatures of 600 - 700 ° C in the or the LNT 5 . 6 will be maintained.

As long as the desulfurization is not completed, it will be between lean and fat Exhaust conditions alternately switched back and forth. The temperatures of 600 - 700 ° C in the or the LNT 5 . 6 will be maintained. In a manner known to the person skilled in the art, it can be ascertained sensory or model-based whether sulfur compounds still exist in the LNT 5 . 6 are present, ie whether the sulfur loading has not fallen below the value LSe. If the sulfur loading is still too high and the desulfurization can not be finished yet (N like No, dt. No), it becomes step S2 returned. If the sulfur load has dropped below a certain threshold and desulphurization can be terminated (Y as Yes, dt. Yes), the process is terminated by no more fuel through the feeders 8th . 9 is supplied. The operation of the internal combustion engine 2 is then normal, ie as required in a particular operating situation, continued.

The inventive method is described below with reference to the state diagram according to 3 explained. After starting the internal combustion engine 2 exhaust gas is produced. If the internal combustion engine is operated with a lean fuel-air mixture, nitrogen oxides contained in the exhaust gas are in the first LNT 5 and in the second LNT 6 absorbed. The particle filter 7 filters out soot particles from the exhaust gas.

The LNT 5 . 6 are regenerated with respect to their nitrogen oxide storage capacities by supplying fuel as a reducing agent. This is done upstream and downstream of each LNT 5 . 6 the nitrogen oxide concentration in the exhaust gas is determined by means of sensors or estimated by means of a model. Exceeds the stored amount of nitrogen oxide LN (LN1 for the first LNT 5 , LN2 for the second LNT 6 ) has a predetermined value LNd (LN1d for the first LNT 5 , LN2d for the second LNT 6 , d for nitric oxide storage regeneration = deNOx), a regeneration of the LNT started by providing stoichiometric conditions. This is done via the first feeder 8th Fuel as reducing agent for the first LNT 5 and via the second feeder 9 Fuel as a reducing agent for the second LNT 6 provided. In addition, the regeneration is ideally carried out in a temperature range of 250 - 400 ° C. This temperature is by means of from the internal combustion engine 2 achieved exhaust gas.

The regeneration of the LNT 5 and or 6 is completed as soon as z. B. is determined by means of a lambda probe that the oxygen concentration in the exhaust stream downstream of a LNT decreases (λ <1), ie, that the intended for regeneration fuel is oxidized by the oxygen in the exhaust stream (lambda breakthrough). The regeneration of the nitrogen oxide storage capacity of the LNT is then completed and it can be used again to store nitrogen oxides from lean exhaust gas.

Desulphurization of the first LNT 5 is started when the sulfur loading LS1 of the first LNT 5 a value LS1d exceeds, which corresponds to a predetermined threshold of sulfur loading, from which the LNT desulfurized (LS1> LS1d). The desulfurization is stopped when the sulfur loading LS1 of LNT falls below a value LS1e, which corresponds to a predetermined threshold value of the sulfur loading, from which the desulfurization of the LNT can be terminated (LS1 <LS1e).

Desulphurization of the second LNT 6 is started when the sulfur loading LS2 the second LNT 6 a value LS2d exceeds, which corresponds to a predetermined threshold of sulfur loading, from which the LNT desulfurized (LS2 <LS2d). The desulfurization is stopped when the sulfur loading LS2 of LNT a value LS2e below a predetermined threshold sulfur loading, from which the desulfurization of the LNT can be terminated (LS2> LS2e).

Is the desulfurization of one or both LNT finished, they are used again during normal operation of the internal combustion engine for storing nitrogen oxides under lean exhaust conditions.

The processes of desulfurization of the first LNT 5 and the second LNT 6 interact with each other. This is especially true in the event that synergy effects can be achieved. Need both LNT 5 . 6 can be done simultaneously. The for the first LNT 5 provided temperature of at least 600 ° C, then can be advantageous for increasing the temperature of the second LNT 6 be used because heat energy with the exhaust gas flow from the first LNT 5 downstream towards the second LNT 6 is transported. In addition, by chemical processes in the interior of the LNT Heat generated (by exothermic reactions). It needs less fuel through the second feeder in this case 9 be initiated to the temperature of the second LNT 6 increase to at least 600 ° C. For the benefit of synergy effects can be a desulfurization of LNT 5 . 6 also be performed overlapping, that is, for example, a desulfurization of the second LNT 6 during the desulfurization of the first LNT 5 is started, or shortly (1 - 10 s) afterwards.

Furthermore, during desulfurization of the first LNT 5 the nitrogen oxide storage capacity of the second LNT 6 be regenerated.

The one between the first LNT 5 and second LNT 6 in the exhaust tract 3 arranged particle filter 10 must also be regenerated if its particle load has exceeded a corresponding threshold. For this purpose, the particles stored in the particulate filter are burned under lean exhaust gas conditions (since oxygen is required). Thereafter, the particulate filter during operation of the internal combustion engine 2 filter new particles from the exhaust gas.

Also, the high temperatures resulting from particulate filter regeneration may assist in desulphurizing the second LNT be used. It needs less fuel through the second feeder in this case 9 be initiated to the temperature of the second LNT 6 increase to at least 600 ° C. The necessary substoichiometric conditions in the second LNT 6 are through by the second feeder 9 provided fuel. The resulting by the regeneration of the particulate filter temperatures and the already reduced oxygen content can also for a regeneration of nitrogen oxide storage capacity of the second LNT 6 be used, wherein by the second feeder 9 In addition, fuel can still be supplied to provide substoichiometric conditions.

It should be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Thus, the method described can also be for a number of more than two LNT be used.

It should be understood that the features of the various exemplary embodiments described herein may be advantageously combined with each other unless specifically stated otherwise. The description is therefore not to be considered in a limiting sense, and the scope of the present invention is defined by the appended claims.

LIST OF REFERENCE NUMBERS

1

arrangement

2

Internal combustion engine

3

exhaust tract

4

LNT system

5

first LNT

6

second LNT

7

particulate Filter

8th

first feeder for reducing agent

9

second supply means for reducing agent

10

control device

11

temperature sensor

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 102016203214 A1 [0003]
• KR 1015274 B1 [0004]

Claims (13)

A method of controlling desulfurization of nitrogen oxide storage catalysts in a nitrogen oxide storage catalytic system in the exhaust tract of an internal combustion engine of an automotive vehicle, the nitrogen oxide storage catalyst system comprising at least one first nitrogen oxide storage catalyst (LNT) and at least one second LNT downstream of the first, at least a first, downstream of the first LNT arranged and at least one second, upstream of the second LNT arranged for supplying a reducing agent in the exhaust tract suitable feed device, the arrangement comprises at least one further exhaust gas aftertreatment device and at least one temperature measuring device, comprising the steps: Providing a temperature sufficient for desulfurization in at least one of the LNTs, Providing substoichiometric exhaust conditions in said LNT for a certain amount of time, Providing over-stoichiometric exhaust conditions in said LNT for a certain amount of time, Changing said exhaust conditions for a given number of cycles while maintaining the temperature of the exhaust gas, and for providing substoichiometric exhaust conditions and said exhaust gas temperature, said reducing agent is introduced by means of the corresponding upstream supply means of said LNT. Method according to Claim 1 wherein the temperature provided for desulfurization is preferably at least 600 ° C. Method according to Claim 1 or 2 wherein fuel is used as said reducing agent. Method according to one of the preceding claims, wherein the first LNT and the second LNT are desulphurized simultaneously, wherein for desulfurization of the first LNT reducing agent via the first supply means and for desulfurization of the second LNT reagent via the second supply means is introduced into the exhaust system. Method according to one of Claims 1 - 3 wherein the first LNT and the second LNT are desulfurized at different times, wherein to desulfurize the first LNT reducing agent via the first supply means and for desulfurization of the second LNT reagent via the second supply means is introduced into the exhaust tract. Method according to one of the preceding claims, wherein the further exhaust aftertreatment device is a particle filter. Method according to Claim 6 wherein simultaneously with a regeneration of the particulate filter, the steps for desulfurization of the second LNT are performed. Method according to one of the preceding claims, wherein the steps for desulfurization of the first and / or second LNT are performed regularly as a function of the operating time of the motor vehicle. Method according to one of Claims 1 - 7 wherein the steps of desulfurizing the first and / or second LNT are performed depending on their respective sulfur loading. Method according to Claim 9 , where the actual sulfur loading of the individual LNT is determined model-based. Method according to Claim 9 or 10 in which the actual sulfur loading of the individual LNT is determined on the basis of sensor data. Arrangement of an internal combustion engine with an exhaust system in a motor vehicle, wherein in the exhaust system at least a first LNT and at least one in the exhaust flow downstream of the first LNT arranged second LNT, at least a first, arranged downstream of the first LNT and at least one second, upstream of the second LNT arranged means for supplying a reagent for enriching the exhaust gas to a substoichiometric ratio suitable means, at least one further exhaust aftertreatment device and at least one temperature measuring device are arranged, the arrangement having a control device which is designed to control the inventive method. Motor vehicle with an arrangement according to Claim 12 ,

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