CN110725735A

CN110725735A - Method for operating an exhaust gas aftertreatment device, control unit for an internal combustion engine and internal combustion engine

Info

Publication number: CN110725735A
Application number: CN201910628930.4A
Authority: CN
Inventors: 托马斯·维特卡
Original assignee: FEV Europe GmbH
Current assignee: FEV Europe GmbH
Priority date: 2018-07-16
Filing date: 2019-07-12
Publication date: 2020-01-24
Also published as: DE102019116775A1; DE102018117188A1

Abstract

A method is described for operating an exhaust gas aftertreatment device of an internal combustion engine, which exhaust gas aftertreatment device comprises a nitrogen oxide storage catalyst, in which nitrogen oxide and sulfur oxide are extracted and stored from the exhaust gas of the internal combustion engine in the case of an oxidizing composition of the exhaust gas, and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein the SCR catalyst is loaded with ammonia such that ammonia reacts with the nitrogen oxide in the case of the oxidizing composition of the exhaust gas with water and nitrogen; and a control unit for an internal combustion engine having an exhaust gas aftertreatment device; and an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein a control unit is provided.

Description

Method for operating an exhaust gas aftertreatment device, control unit for an internal combustion engine and internal combustion engine

Technical Field

The invention relates to a method for operating an exhaust gas aftertreatment device of an internal combustion engine, comprising a nitrogen oxide storage catalyst, in which nitrogen oxide and sulfur oxide are extracted and stored from the exhaust gas in the case of an oxidizing composition of the exhaust gas of the internal combustion engine, and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein the SCR catalyst is loaded with ammonia such that in the case of the oxidizing composition of the exhaust gas, the ammonia reacts with the nitrogen oxide to form water and nitrogen. The invention further relates to a control unit for an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein the SCR catalyst is charged with ammonia, such that, in the case of an oxidizing composition of the exhaust gas, the ammonia reacts with the nitrogen oxide in the SCR catalyst to form water and nitrogen. The invention also relates to an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein a control unit is provided.

Background

In the aftertreatment of the exhaust gases of internal combustion engines, it is known to use a plurality of different systems in order to reduce the emissions of undesirable constituents of the exhaust gases. These systems furthermore comprise a nitrogen oxide storage catalyst and an SCR catalyst, by means of which the proportion of nitrogen oxides (NOx) in the exhaust gas is reduced. In a Selective Catalytic Reduction (SCR) method, a urea-water solution is introduced into an oxygen-rich exhaust gas. In the SCR catalyst, the urea-water solution reacts to form ammonia, which is subsequently combined with nitrogen oxides, thereby producing water and nitrogen. Nitrogen oxides are stored in the nitrogen storage catalyst in the case of lean-burn, i.e. likewise oxygen-rich, exhaust gases. The operating conditions of the internal combustion engine are temporarily changed so that there is a lack of oxygen in the exhaust gas and, therefore, a rich exhaust gas. The stored nitrogen oxide can now be reduced to harmless nitrogen, which is subsequently discharged. In addition to nitrogen oxides, a specific amount of sulfur oxides is usually stored in the NOx storage catalyst. Since these stored sulfur compounds, also called sulfates, have a higher stability than the corresponding nitrogen compounds, also called nitrates, they accumulate continuously in the nitrogen oxide storage catalyst. Therefore, the nitrogen oxide storage catalyst must sometimes be desulfated. A prerequisite for such desulfation is the increased temperature in the nitrogen oxide storage catalyst together with the substoichiometric, i.e. rich, exhaust gas composition. The systems are operated independently of one another, for example, in each case according to a characteristic map which describes the operating state of the catalytic converter, the operating point of the exhaust gas sensor system and the internal combustion engine.

DE 102007041501B 4 describes, for example, a method for cleaning the exhaust gas of an internal combustion engine, wherein an exhaust gas system has a NOX storage catalytic converter device and an SCR catalytic converter device. A NOX storage catalytic converter device, in which a substoichiometric exhaust gas composition is present for the purpose of its sulfate removal, and a predetermined amount of the sulfur compounds thus freed are passed together with an exhaust gas flow having a lean exhaust gas composition to the SCR catalytic converter device, in which the hydrogen sulfide present in the sulfur compounds is oxidized, are arranged in partial exhaust gas lines associated with different cylinder banks.

Disclosure of Invention

The object of the invention is to operate a nitrogen oxide storage catalyst and at least one SCR catalyst in an exhaust gas aftertreatment device when the exhaust gas of an internal combustion engine is being treated, wherein the regulation of the exhaust gas aftertreatment device takes into account a plurality of systems.

The object is achieved according to the invention by a method and a control unit for operating an exhaust gas aftertreatment device of an internal combustion engine. Preferred embodiments and advantageous refinements are given in the following description.

The method according to the invention is used for operating an exhaust gas aftertreatment device of an internal combustion engine, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst. In the case of an oxidizing composition of the exhaust gas of an internal combustion engine, nitrogen oxides and sulfur oxides are extracted from the exhaust gas in a nitrogen oxide storage catalyst and stored therein. According to the invention, the SCR catalytic converter is charged with ammonia, so that, in the case of an oxidizing composition of the exhaust gas, the ammonia reacts with the nitrogen oxides to form water and nitrogen, wherein the charging of the SCR catalytic converter with ammonia is adjusted taking into account the nitrogen oxide storage catalytic converter.

The method according to the invention has the advantage that depending on the state of the nitrogen oxide storage catalyst, the loading of the SCR catalyst with ammonia can be kept low, so that ammonia slip, i.e. slip, is avoided. It is also advantageous if the sulfur loading of the nox storage catalyst is high, in order to compensate for the reduced nox conversion of the nox storage catalyst, the loading of the SCR catalyst with ammonia can be increased.

Nitrogen oxide storage catalysts are known from the prior art. The nitrogen oxide storage catalyst is also referred to as a NOx storage catalyst (NSK), a NOx trap or a Lean NOx Trap (LNT). NOx here means not only nitric oxide NO, but also nitrogen dioxide NO 2. When using a nitrogen oxide storage catalyst, the internal combustion engine is usually operated lean, which enables low fuel consumption. The exhaust gas thus has an oxidizing composition with excess air. The exhaust gas containing nitrogen oxides is fed to a nitrogen oxide storage catalyst, which extracts nitrogen oxides from the exhaust gas by storage, currently as nitrate storage. Depending on the amount of stored nitrogen oxides, nitrate regeneration of the storage catalyst is sometimes performed. For this purpose, the internal combustion engine is switched over in a short time to rich operation, whereby a rich exhaust gas is produced, which has an excess of reducing agents, such as carbon monoxide, hydrogen or hydrocarbons, i.e. a reducing composition. This causes the release of the nitrogen oxides stored in the nitrogen oxide storage catalyst.

The term SCR catalyst for the purposes of the present invention generally includes catalyst systems which apply the principle of selective catalytic reactions and otherwise function without limitation. The term includes, in particular, so-called SCRF or SDPF catalysts, in which the SCR coating on the particle filter is functionally integrated.

Preferably, an aqueous urea solution or a urea-water solution is injected into the exhaust gas line upstream of the SCR catalytic converter, for example by means of a dosing pump or an injector. Ammonia and CO2 are produced from the urea-water solution by a hydrolysis reaction. The ammonia (NH3) thus produced reacts with the nitrogen oxides in the exhaust gas at a corresponding temperature substantially in the SCR catalyst. Ammonia is also produced in the nitrogen oxide storage catalyst during the nitrate regeneration, which is trapped in the SCR catalyst and is converted together.

The combustion air ratio is also synonymously referred to herein as the air-fuel ratio, abbreviated as Lambda (Lambda). The designations air ratio or air number are also common for dimensionless characteristic numbers which describe the mass ratio of air to fuel in the combustion process. A combustion air ratio of less than 1(λ <1) indicates a lack of air, which in the case of internal combustion engines refers to a rich or rich mixture (reiche Gemisch), which produces exhaust gases with a reducing composition. Combustion air ratios greater than 1(λ >1) indicate excess air, which in the case of internal combustion engines is referred to as lean mixtures or lean mixtures (armen Gemisch), which produces exhaust gases with a reducing composition. The regulation, also referred to as lambda regulation, is preferably carried out in gasoline engines by direct intervention of the injected fuel quantity, and in diesel engines by adjusting the exhaust gas recirculation rate via an exhaust gas recirculation device, preferably via an air system.

The desulfation of the nox storage catalyst is preferably carried out by setting the reducing composition of the exhaust gas and increasing the exhaust gas temperature such that the sulfur oxides stored in the nox storage catalyst are released under the formation of hydrogen sulfide. During the desulphation, the hydrogen sulphide released by the nitrogen oxide storage catalyst is supplied to the SCR catalyst and is oxidised in the SCR catalyst to sulphur dioxide under the conditions of the reducing composition of the exhaust gas. The desulfation of the nox storage catalyst is preferably carried out as soon as the sulfur oxide loading of the nox storage catalyst reaches a loading limit value, which is determined in particular taking into account the state of the SCR catalyst.

According to the invention, the state of the nitrogen oxide storage catalyst is evaluated as a function of the thermal life of the nitrogen oxide storage catalyst and/or as a function of the sulfur oxide loading.

According to a preferred embodiment, the loading of the SCR catalytic converter with ammonia is increased with an increase in the thermal life of the nitrogen oxide storage catalytic converter.

According to a preferred embodiment, the loading of the SCR catalytic converter with ammonia is increased with an increased sulfur oxide loading of the nitrogen oxide storage catalytic converter. It is particularly preferred to carry out the desulphatation of the nitrogen oxide storage catalyst from time to time, the loading of the SCR catalyst with ammonia dropping again after the desulphatation.

A further subject matter of the invention relates to a control unit for an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst. The SCR catalyst is charged with ammonia, so that, in the case of an oxidizing composition of the exhaust gas, the ammonia reacts with the nitrogen oxides in the SCR catalyst to form water and nitrogen. The control unit is designed according to the invention to regulate the loading of the SCR catalytic converter with ammonia, taking into account the state of the nox storage catalytic converter.

Preferably, the control unit is designed to evaluate the state of the nox storage catalyst as a function of the thermal life of the nox storage catalyst and the sulfur oxide loading.

The control unit is also preferably designed to perform the desulphatation of the nitrogen oxide storage catalyst in some cases in such a way that the internal combustion engine produces an exhaust gas with a reducing composition and with an increased temperature during the desulphatation, so that the sulphur oxide stored in the nitrogen oxide storage catalyst is released under the formation of hydrogen sulphide and is oxidised to sulphur dioxide in the SCR catalyst under the reducing composition of the exhaust gas. The control unit is also preferably designed to perform a desulfation of the nox storage catalyst as soon as the sulfur oxide loading of the nox storage catalyst reaches a loading limit value, wherein the control unit is designed in particular to variably determine the loading limit value taking into account the state of the SCR catalyst.

Furthermore, it is preferred that the control unit is designed to carry out the method described above.

A further subject matter of the invention relates to an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein a control unit as described above is also provided.

Drawings

The invention is explained in detail below with reference to the figures according to embodiments. The embodiments are equally related to the overall inventive subject matter, which is only exemplary and does not limit the general inventive concept.

The figures show:

figure 1 shows a schematic block diagram of an internal combustion engine with an associated exhaust gas aftertreatment device according to an embodiment of the invention,

figure 2 shows a schematic block diagram of a variant of an exhaust gas aftertreatment device according to another embodiment of the invention,

fig. 3 shows a schematic block diagram of a further variant of an exhaust gas aftertreatment device according to a further embodiment of the invention.

Detailed Description

In the embodiment shown in fig. 1, a diesel engine is used as the internal combustion engine 1. Combustion air is supplied to the internal combustion engine 1 via the intake air line 3. An exhaust gas aftertreatment device 2 is associated with the internal combustion engine 1, which exhaust gas aftertreatment device has an oxidation catalyst 5, a particle filter 6, a nitrogen oxide storage catalyst 7 and an SCR catalyst 8 in an exhaust gas line 4. In the present case, on the one hand, the particle filter 6 is connected directly downstream of the oxidation catalytic converter 5, and on the other hand, the SCR catalytic converter 8 is connected directly downstream of the nitrogen oxide storage catalytic converter 7. The temperature of the nitrogen oxide storage catalyst 7 is measured by means of a sensor 15. Upstream of the oxidation catalytic converter 5, an exhaust gas turbocharger 12 is installed in the exhaust gas line 4 for compressing the combustion air, which after compression is cooled by a charge air cooler 14 arranged in the intake air line 3. Furthermore, a control unit 9 is associated with the internal combustion engine 1, which control unit is also used to control the combustion. In order to transmit the control signals necessary for this, a control or signal line 10 is present. Other components for measuring and controlling operating parameters, such as oxygen probes, temperature sensors, throttle valves, other signal lines, etc., are not shown in the figures for the sake of overview.

The internal combustion engine 1 is initially operated lean. The particulates contained in the exhaust gas are intercepted in the particulate filter 6. As the exhaust gas passes through the oxidation catalytic converter 5, NO contained in the exhaust gas is oxidized to NO2 and can subsequently oxidize the carbonaceous particles accumulated there in the downstream connected particulate filter 6, as a result of which a continuous regeneration of the particulate filter 6 takes place. The exhaust gas flowing out of the particle filter, which additionally contains nitrogen oxides, is fed to a nitrogen oxide storage catalytic converter 7, which catalytic converter 7 extracts nitrogen oxides from the exhaust gas by storage, currently as nitrate storage. Depending on the amount of stored nitrogen oxides, nitrate regeneration of the storage catalyst 7 is sometimes performed. For this purpose, the internal combustion engine 1 is switched to a rich operation in a short time, thereby generating a rich exhaust gas which has an excess of reducing agent, such as carbon monoxide, hydrogen or hydrocarbons. This causes the release of nitrogen oxides stored in the nitrogen oxide storage catalyst 7, which are reduced by the reducing agent of the exhaust gas at the centers of the precious metals present in the catalytic layer of the nitrogen oxide storage catalyst 7. The temperature of the nox storage catalyst 7 is determined by means of the sensor 15, since the nitrate regeneration is only carried out if the temperature of the nox storage catalyst 7 exceeds a temperature limit value.

The combustion air ratio is also synonymously referred to herein as the air-fuel ratio, abbreviated as λ. In the case of gasoline engines, the control, also referred to as lambda control, is therefore carried out by direct intervention of the injected fuel quantity, which is not usual in diesel engines, since in diesel engines the engine torque is controlled via a change in the fuel quantity. Instead, lambda regulation in diesel engines takes place via an air system by adjusting the exhaust gas recirculation rate via the exhaust gas recirculation device 11.

Nitrogen gas is mainly produced as a reduction product of the reduction of nitrogen oxide. Additionally, depending on the conditions under which the nitrate regeneration is carried out, a greater or lesser amount of the reduction product ammonia (NH3) is also formed, the release of which into the environment is undesirable. By means of the SCR catalyst 8 according to the invention, which is arranged downstream of the nitrogen oxide storage catalyst 7, ammonia is trapped by the storage. The stored NH3 is supplied as an additional reducing agent to the selective nitrogen oxide reduction in the SCR catalytic converter 8 during lean internal combustion engine operation following nitrate regeneration. The efficiency of the nitrogen oxide removal in the exhaust gas aftertreatment device 2 is thereby additionally increased in an advantageous manner.

When using sulfur-containing fuels, the exhaust gases of the internal combustion engine 1 contain sulfur dioxide, which is absorbed by the catalyst material of the nitrogen oxide storage catalyst 7 to form stable sulfates, which over time reduce its nitrogen oxide storage capacity more and more. The nitrogen oxide storage catalyst 7 thus repeatedly removes the accumulated sulfur during desulphation (desulphurisation), i.e. regeneration. For this purpose, the internal combustion engine 1 is operated in the desulfurization operation mode. The desulfurization operation mode includes causing the exhaust gas temperature to increase to over 500 c, for example, by fuel reinjection and setting the reducing exhaust gas component to a value of about 0.95 or less for the air-fuel ratio (λ), similar to that for the purpose of nitrate regeneration. Under these conditions: the relatively stable sulfates are reductively decomposed in the nitrogen oxide storage catalyst 7. Depending on the temperature, the extent of the increase in concentration and the amount of sulfur stored in the nitrogen oxide storage catalyst, a greater or lesser amount of hydrogen sulfide (H2S) is produced. However, H2S is converted into sulfur dioxide (SO2) with a low odor in nitrogen oxide storage catalyst 7 and in SCR catalyst 8 under the reducing conditions of desulfurization. This avoids the odor problems normally associated with the desulfurization of nitrogen oxide storage catalysts, which is also referred to herein as desulfurating. The use of the SCR catalyst 8 downstream of the nox storage catalyst 7 has the advantage that the process control of the desulfation can be simplified thereby, since it is not necessary to achieve a minimization of the undesired desulfation product H2S. For example, the desulfates can be significantly shortened by a stronger enrichment with a lambda value of less than 0.95 and a stronger and faster H2S release from the nox storage catalyst 7 associated therewith.

The SCR catalytic converter 8 is charged with ammonia, so that in the case of an oxidizing composition of the exhaust gas, the ammonia reacts with the nitrogen oxides to form water and nitrogen, wherein the charging of the catalytic converter 8 with ammonia SCR is regulated taking into account the state of the nitrogen oxide storage catalytic converter 7, in particular taking into account the thermal life of the nitrogen oxide storage catalytic converter 7 and/or the specification of sulfur oxides. The method according to the invention has the advantage that the loading of the SCR catalyst 8 with ammonia can be kept low depending on the state of the nitrogen oxide storage catalyst 7, so that ammonia slip, i.e. slip, is avoided.

Upstream of the SCR catalytic converter 8, a feed line for an aqueous urea solution 16 is provided. In the SCR catalytic converter 8, the urea-water solution reacts to form ammonia, which then combines with the nitrogen oxide, from which water and nitrogen gas are produced. The loading of the SCR catalytic converter 8 with ammonia is preferably regulated by the amount of urea-water solution added.

The control unit 9 of the internal combustion engine 1 is preferably designed to perform the desulfation of the nitrogen oxide storage catalyst 7 at times in such a way that the internal combustion engine 1 generates an exhaust gas with a reducing composition and with an increased temperature during the desulfation, so that the sulfur oxide stored in the nitrogen oxide storage catalyst 7 is released under the formation of hydrogen sulfide. The control unit 9 is designed to perform a desulfation of the nox storage catalyst 7 as soon as the sulfur oxide loading of the nox storage catalyst reaches a loading limit value, wherein the control unit 9 is designed in particular to determine the loading limit value taking into account the state of the SCR catalyst 8, in particular taking into account the thermal life of the SCR catalyst 8.

The availability of the SCR catalytic converter 8 downstream of the nox storage catalytic converter 7 is independent of the presence of cleaning components connected upstream, such as the particle filter 6 and the oxidation catalytic converter 5. H2S can also be oxidized in the nox storage catalyst 7. The SCR catalytic converter 5 is not absolutely necessary for this purpose.

Fig. 2 and 3 show a variant of an exhaust gas aftertreatment device 2, which is typically used with an internal combustion engine according to the invention. Reference is made to fig. 1 with regard to an embodiment of elements of the internal combustion engine which are not shown.

Fig. 2 shows a schematic block diagram of a variant of an exhaust gas aftertreatment device 2, in which a nitrogen oxide storage catalyst 7,

SCR catalysts

6, 8 with a first combination of filters, a so-called SCRF (Selective Catalytic Reduction Filter) and a second SCR catalyst 8 are arranged in succession in the flow direction of the exhaust gas. SCRF is a combination of an SCR catalyst 8 and a particulate filter 6, which for the purposes of the present invention belongs to the SCR catalyst. A feed line for the aqueous urea solution 16 is provided upstream of the SCR catalytic converters 8. The second supply line for the downstream aqueous urea solution 16 and the second SCR catalyst are optional.

Fig. 3 shows a schematic block diagram of a further variant of an exhaust gas aftertreatment device 2, in which a nitrogen oxide storage catalytic converter 7, a particle filter 6 and an SCR catalytic converter 8 are arranged in succession in the flow direction of the exhaust gas. Upstream of the SCR catalytic converter 8, a feed line 16 for the aqueous urea solution is provided.

List of reference numerals

1 internal combustion engine

2 exhaust gas aftertreatment device

3 suction air line

4 waste gas line

5 Oxidation catalyst

6 particulate filter

7 nitric oxide storage catalyst

8 SCR catalyst converter

6. 8 SCRF, combined SCR catalyst with particulate filter

9 control unit

10 signal line

11 exhaust gas return device

12 exhaust gas turbocharger

14 charge air cooler

15 sensor

16 introduction line of aqueous urea solution

Arrow A, flow direction

Claims

1. Method for operating an exhaust gas aftertreatment device of an internal combustion engine, comprising a nitrogen oxide storage catalyst (7) and at least one SCR catalyst (8) arranged downstream of the nitrogen oxide storage catalyst (7),

wherein nitrogen oxides and sulfur oxides are extracted and stored from the exhaust gas in the nitrogen oxide storage catalyst (7) in the case of an oxidizing composition of the exhaust gas of the internal combustion engine,

wherein the SCR catalyst (8) is charged with ammonia such that, in the case of an oxidizing composition of the exhaust gas, the ammonia reacts with the nitrogen oxides in the SCR catalyst (8) to form water and nitrogen,

wherein the loading of the SCR catalyst (8) with ammonia is regulated taking into account the state of the nitrogen oxide storage catalyst (7).

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

evaluating the state of the nitrogen oxide storage catalyst (7) as a function of one or more of the following characteristics: thermal life and sulfur oxide loading of the nitrogen oxide storage catalyst.

3. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the loading of the SCR catalyst (8) with ammonia is increased when the thermal life of the nitrogen oxide storage catalyst is increased.

4. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

in the case of an increased sulfur oxide treatment of the nitrogen oxide storage catalyst, the loading of the SCR catalyst (8) with ammonia is increased.

5. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

the desulfation of the nitrogen oxide storage catalyst (7) is sometimes carried out, wherein the loading of the SCR catalyst (8) with ammonia is reduced again after the desulfation.

6. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

adding a urea-water-solution (16) to the exhaust gas upstream of the SCR catalyst (8), wherein the urea-water-solution reacts into ammonia in the SCR catalyst (8), wherein the loading of the SCR catalyst with ammonia is regulated via the amount of urea-water-solution added.

7. A control unit (9) for an internal combustion engine (1) having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst (7) and at least one SCR catalyst (8) arranged downstream of the nitrogen oxide storage catalyst (7), wherein the SCR catalyst (8) is loaded with ammonia such that, in the case of an oxidizing composition of the exhaust gas, the ammonia reacts with the nitrogen oxide to form water and nitrogen, wherein the control unit (9) is designed to regulate the loading of the SCR catalyst (8) with ammonia taking into account the state of the nitrogen oxide storage catalyst (7).

8. The control unit of claim 7, wherein,

it is characterized in that the preparation method is characterized in that,

the control unit (9) is designed to evaluate the state of the nitrogen oxide storage catalyst (7) as a function of one or more of the following characteristics: thermal life and sulfur oxide loading of the nitrogen oxide storage catalyst.

9. The control unit of claim 7 or 8,

it is characterized in that the preparation method is characterized in that,

the control unit (9) is designed to carry out the method according to any one of claims 1 to 6.

10. An internal combustion engine (1) having an exhaust gas aftertreatment device,

wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst (7) and at least one SCR catalyst (8) arranged downstream of the nitrogen oxide storage catalyst (7), wherein a control unit (9) according to one of claims 7 to 9 is also provided.