Exhaust aftertreatment device and method

Abstract

A method for carrying out exhaust gas aftertreatment in an exhaust gas aftertreatment device (11) comprising an exhaust gas passage (12), an adsorption catalyst (14) and a reducing agent catalyst (15), wherein the adsorption catalyst (14) and the reducing agent catalyst (15) are arranged in a loop section (13) of the exhaust gas passage (12), characterized in that the method comprises the following steps: - Determining an exhaust gas temperature (T); - Reversing the flow direction of the exhaust gas within the loop section (13) based on the determined temperature, starting from a basic direction (BD) running from the adsorption catalyst (14) through the reducing agent catalyst (15), to a reverse direction (RD) running from the reducing agent catalyst (15) through the adsorption catalyst (14), when the determined temperature (T, Ta) exceeds a first threshold value that corresponds to an adsorption active maximum temperature (T1). corresponds.

Description

The invention relates to a technology for exhaust gas aftertreatment, in particular an exhaust gas aftertreatment method and an exhaust gas aftertreatment device according to the preamble of the respective independent claim.US 2006 / 0 260 296 A1 shows a process for post-treatment of the exhaust gas. WO 2010 / 134167 A1 discloses an abnormality diagnosis apparatus for nitrogen oxide sensors.Currently known technologies for exhaust gas aftertreatment are not optimally designed. In particular, the effectiveness of a combined NOx storage and NOx conversion process using a NOx adsorption catalyst and a NOx reducing agent catalyst may be temporarily lowered in an operating phase in which the exhaust temperature rises through a temperature gap between the temperature ranges in which NOx adsorption and NOx conversion are highly efficient. The temperature rise can occur in particular starting from a temperature which is within an adsorption temperature window, then rise over the temperature gap and reach a reduction temperature window.The adsorption temperature window may extend from a lower limit to an "adsorption active maximum temperature". The reduction temperature window may extend from a "reduction active minimum temperature" to an upper limit of the temperature. When the exhaust gas temperature is within the adsorption temperature window, NOx can be stored in the NOx adsorption catalyst with good efficiency. When the exhaust temperature is within the reduction temperature window, NOx can be converted within the NOx reductant catalyst with good efficiency. However, between the maximum active temperature adsorption and the minimum active temperature reduction, i.e., between the adsorption temperature window and the temperature window reduction, there is a temperature gap within which the overall effectiveness of combined NOx storage and NOx conversion may be reduced or inefficient.It is an object of the present invention to provide an improved exhaust gas aftertreatment technique, in particular an exhaust gas aftertreatment method and an exhaust gas aftertreatment device, with which the effectiveness of the NOx reduction can be increased. The invention achieves this object by the characterizing features of the respective independent claim.The method for performing exhaust gas after-treatment according to the present disclosure is performed in or through the use of an exhaust gas after-treatment device including an adsorption catalyst and a reducing agent catalyst disposed in a loop portion of an exhaust passage. The loop portion may be a portion of the exhaust passage connected to the other parts of the exhaust passage through a switching valve. The switching valve is for connecting the exhaust gas inflow, in particular a part of the exhaust passage which is connected to an internal combustion engine, to one end of the loop section and for connecting the respective other end of the loop section to the exhaust gas outflow, in particular to a part of the exhaust passage leading to the tail pipe. In a switching event, the end ports of the loop portion may be exchanged for inflow and outflow of exhaust gas.The method comprises the following steps: a temperature, in particular a momentary exhaust gas temperature, within the exhaust passage is determined. The flow direction of the exhaust gas within the loop section is reversed based on the determined temperature, in particular based on a comparison of the determined exhaust gas temperature with one or more temperature thresholds.By reversing the flow direction of the exhaust gas, the transport path within the loop section can be temporarily extended before entering the adsorption catalyst, whereby the exhaust gas temperature before entering the Nox adsorption catalyst can be reduced by increased heat loss effects. Consequently, an exhaust gas having a reduced temperature may be temporarily supplied to or through the adsorption catalyst, enabling storage or conversion of NOx with increased efficiency, particularly in a period in which the exhaust gas temperature is within the temperature gap.Any suitable temperature parameter may serve as the detected temperature indicated in the claims, in particular an exhaust gas temperature or temperature in the catalyst bed which is detected or estimated. Alternatively or additionally, a temperature parameter retrieved from an external device may serve as the detected temperature. In particular, one or a combination of the following temperature parameters can form the detected temperature:• exhaust gas temperature at the entry point to the loop section;• exhaust gas temperature before or at the adsorption catalyst;• exhaust gas temperature before or at the reducing agent catalyst;• bed temperature or surface temperature of the adsorption catalyst;• Bed temperature or surface temperature of reducing agent catalyst.The exhaust flow may be reversed from a base direction passing from the adsorption catalyst through the reductant catalyst to a reverse direction passing from the reductant catalyst through the adsorption catalyst in a first switching event based on the determined temperature. The first switching event can be triggered when the detected temperature becomes active maximum temperature higher than the adsorption, i.e. when the detected temperature leaves the adsorption temperature window and enters the temperature gap. The determined temperature, which is compared to the threshold for triggering the first switching event, may be, in particular, the exhaust gas temperature at an entry point to the loop section or an exhaust gas temperature before or at the adsorption catalyst or a bed temperature or surface temperature of the adsorption catalyst.The exhaust flow may be reversed in a second switching event based on the determined temperature from the opposite direction to the base direction within the loop portion of the exhaust passage. The second changeover event can be triggered if the detected temperature becomes active minimum temperature by a tolerance value higher than the reduction. The determined temperature, which is compared to the threshold for triggering the second switching event, may be, in particular, the exhaust temperature at an entry point to the loop section or an exhaust temperature before or at the reductant catalyst or a bed temperature or surface temperature of the reductant catalyst.An exhaust after-treatment device according to the present disclosure is designed to be used in combination with the exhaust after-treatment method of the present disclosure. The exhaust after treatment device includes an exhaust passage, an adsorption catalyst for storing Nox, and a reducing agent catalyst for selectively reducing Nox. The selective reduction of NOx is preferably carried out in the presence of a reducing agent.The exhaust after treatment device includes a loop portion in the exhaust passage and a switching valve. The adsorption catalyst and the reducing agent catalyst are disposed in the loop portion. The switching valve is configured to reverse the exhaust flow through the loop portion.The exhaust gas aftertreatment device may comprise a temperature detection means, in particular at least one temperature sensor and a control unit for triggering the reversal of the exhaust gas flow. The control device is designed to monitor the detected temperature and compare it with at least one threshold value. The detected temperature can be compared in particular with respect to the active maximum temperature relative to the adsorption and with respect to a switching threshold value which is active minimum temperature by a tolerance value higher than the reduction.The controller is preferably configured to perform the exhaust after treatment method according to the present disclosure. It may in particular cause a reversal of the exhaust flow in the following cases.Case 1: The exhaust gas flow is reversed from the base direction to the opposite direction when the detected temperature leaves the adsorption temperature window.Case 2: The exhaust flow is reversed from the opposite direction to the base direction when the detected temperature at the reductant catalyst increases above the switching threshold.The exhaust aftertreatment method may be in the form of a software product including instructions to perform the method. The software product can be stored on a physical data memory and / or it can be executed within a data processing means, in particular within the control unit of the exhaust gas aftertreatment device.Further advantageous embodiments of the invention are defined in the dependent claims.The invention is illustrated by way of example and schematically in the drawings. They show: FIG. 1 is a schematic diagram of an exhaust after treatment device in which the exhaust gas flows in a base direction through a loop portion in the exhaust passage; FIG. 2 : shows a schematic illustration analogous to FIG. 1, here with exhaust gas flowing in the opposite direction; FIG. 3 shows a characteristic curve which represents various switching points of a switching valve or corresponding control commands for actuating the switching valve; FIG. 4 : shows a characteristic curve for explaining a detected temperature, in particular temperatures at or in the catalytic converters, wherein the temperature profiles result from the selected exhaust gas flow directions; FIG. 5 is a characteristic curve for explaining the addition of ammonia into the exhaust gas before reaching the exhaust gas reducing agent catalyst and / or an amount of the reducing agent stored in the reducing agent catalyst;The exhaust gas after treatment device ( 11) according to the present disclosure will be explained by way of an example illustrated in FIGS. 1 and 2.The exhaust gas aftertreatment device ( 11) comprises an exhaust passage ( 12), which can be configured as desired. It may comprise a first part connected to an internal combustion engine (10). The first part may form or define the exhaust gas inflow (18) of the exhaust gas. A central part of the exhaust passage (12) is a looped portion having a first end and a second end, which may alternatively be connected to the exhaust inflow (18) through a switching valve (17). The other end thereof may be connected through the switching valve (17) to an exhaust outflow (19) which may be formed or defined by another part of the exhaust passage (12), particularly an end portion extending to a tail pipe where the exhaust gas is discharged into the atmosphere.Exhaust gas having a certain NOx content (nitrogen oxides) enters the loop portion (13) of the exhaust passage (12) via the switching valve (17). In or on the loop passage ( 13), the NOx adsorption catalyst ( 14) (also called passive NOx adsorber (PNA)) and the reducing agent catalyst ( 15) (also called selective NOx reducing agent catalyst, SCR) are arranged. The exhaust gas entering the loop portion (13) at one end is sequentially passed through the NOx adsorption catalyst (14) and the reducing agent catalyst (15) before leaving the loop portion at the other end. The order of passage through the catalytic converters (14, 15) depends on the instantaneous direction of flow (BD, RD) of the exhaust gas, which is controlled by the switching position of the switching valve (17).In the base direction (BD) shown in FIG. 1, the exhaust gas first flows through the adsorption catalyst ( 14) and then through the reducing agent catalyst. In the opposite direction (RD) shown in FIG. 2, the exhaust gas flows in the opposite direction, i.e. first through the reducing agent catalyst ( 15) and then through the adsorption catalyst ( 14).Heat loss may occur as it flows through the exhaust passage ( 12) and in particular through the loop section ( 13), i.e. a portion of the heat contained in the exhaust gas is continuously emitted to a wall of the exhaust passage ( 12) or to any exhaust gas aftertreatment component arranged in or on the exhaust passage ( 12). Due to the heat loss phenomenon, the exhaust gas temperature (T) decreases during the flow of the exhaust passage (12) and the loop portion (13).The change of the exhaust gas temperature(s) is explained in FIG. 4. There, the graphs (Ta', Tr') represented by the one-dot chain line and the two-dot chain line represent the temperature behavior in a case where the flow direction is not reversed. The graphs (Ta, Tr) shown by a solid line and a broken line represent the temperature behavior in a case where the flow direction is reversed.The adsorption catalyst (14) traps NOx from the exhaust gas flowing therethrough. The trapped NOx remains stored in the adsorption catalyst (14) as long as the (local and momentary) exhaust temperature (Ta) is within the adsorption temperature window (29). If the (local and instantaneous) exhaust temperature (Ta, Ta') at or within the adsorption catalyst (14) actively exceeds the maximum temperature (T1), no additional NOx can be stored in the adsorption catalyst (14). Rather, the stored NOx is released. When the basic direction is maintained and when the temperature of the exhaust gas (10) supplied from the internal combustion engine rises, the (local and momentary) exhaust gas temperature (Ta') at or within the adsorption catalyst (14) will also increase (indicated by the dot-and-dash line). While the exhaust gas temperature is within the intermediate temperature interval ( 36), i.e., is greater than the adsorption active maximum temperature (T 1) and is less than the reduction active minimum temperature (T 2), the NOx generated by the internal combustion engine ( 10) cannot be stored or converted with good or sufficient efficiency.When the exhaust gas temperature (T) further increases, in particular, when the (local and momentary) exhaust gas temperature (Tr) at or within the reducing agent catalyst (15) actively reaches or exceeds the minimum temperature (T2), NOx can be converted in the reducing agent catalyst (15) with good or sufficient efficiency.The exhaust flow direction is reversed from the base direction (BD) to the opposite direction (RD) (during the time period in which the temperature of the exhaust gas fed from the internal combustion engine (10) rises). The reversal of the flow direction is carried out on the basis of the detected temperature, in particular if the (local and instantaneous) exhaust gas temperature (Ta) at or in the adsorption catalyst (14) becomes higher than the adsorption active maximum temperature (T1).Thereby, the exhaust gas supplied from the internal combustion engine having a temperature above the adsorption temperature window (29) is first supplied to the reducing agent catalyst (15) and then flowed into the adsorption catalyst (14). Due to the heat loss, the (local and momentary) temperature (Ta) of the exhaust gas at or within the adsorption catalyst (14) is consequently reduced. Therefore, the NOx contained in the exhaust gas can be further stored. As can be seen from FIGS. 3 and 4, in the first changeover event ( 30), which is triggered by the control unit ( 20), in particular by generating a countercurrent command ( 27), the course of the (local and instantaneous) exhaust gas temperature (Ta) on the adsorption catalytic converter ( 14) decreases again (compared with the temperature course (Ta') without reversing the exhaust gas flow).Because the hot exhaust gas is first conducted to the reducing agent catalytic converter ( 15), the (local and momentary) exhaust gas temperature (Tr) at or in the reducing agent catalytic converter ( 15) increases in turn (compared to the temperature profile (Tr') without reversing the exhaust gas flow). Consequently, the reduction temperature window (28) can be reached more quickly.During the first time phase (23) in which the base direction (BD) is present, i.e. in which the control device outputs a normal flow command (26), and also during a second time phase (24) in which the opposite direction predominates, i.e. in which the control device outputs a counter flow command (27), the NOx contained in the exhaust gas is stored in the adsorption catalytic converter.The stored NOx escapes from the adsorption catalyst when the (local and momentary) exhaust gas temperature (Ta) actively exceeds the maximum temperature (T1). However, this may occur at a time when an efficient NOx conversion can already be performed within the reducing agent catalyst (15).In the base direction (BD), the released NOx continues to flow to the reducing agent catalyst (15). It is therefore advantageous to carry out the second changeover event ( 31) in a time phase in which the (local and instantaneous) exhaust gas temperature (Tr) at or within the reducing agent catalytic converter ( 15) has actively reached or exceeded the reduction minimum temperature (T 2). In the reducing agent catalyst, NOx is reduced due to a chemical reaction with a reducing agent. The NOx reduction takes place in the reducing agent catalyst when sufficient reducing agent is stored in the reducing agent catalyst (15) or is supplied into the reducing agent catalyst (15) together with the exhaust gas.Due to the second switching event (31), the changed flow direction and the phenomenon of heat loss again lead to a change of the (local and instantaneous) exhaust temperatures (Ta, Tr) along the loop section. In particular after the second changeover event ( 31), the exhaust gas ( 10) supplied by the internal combustion engine is first conducted to the adsorption catalytic converter ( 14) and then to the reducing agent catalytic converter ( 15). Consequently, the (local and instantaneous) exhaust temperature (Tr) will reach a local maximum during the second switching event (31) and may then drop again. If the second changeover event ( 31) were to be carried out if the detected temperature (T), in particular the (local and instantaneous) exhaust gas temperature (Tr), actively reaches the minimum temperature reduction, the temperature would decrease again and the reduction actively falls below the minimum temperature (T 2), which leads to inadequate NOx conversion performance.It is therefore advantageous to carry out the second changeover event ( 31) (at a later point in time) (namely) when the detected temperature (T) has reached the switching threshold value (T 3), which is actively minimum temperature by a predefined tolerance value higher than the reduction.According to the present disclosure, a reducing agent is preferably added to the exhaust gas within the exhaust passage ( 12). Specifically, the reducing agent injection may be performed in a part of the loop portion between the adsorption catalyst ( 14) and the reducing agent catalyst ( 15). For this purpose, the exhaust gas aftertreatment device may comprise a reducing agent injector, which may be arranged in particular in the loop section between the NOx adsorption catalyst ( 14) and the reducing agent catalyst ( 15).Any reducing agent may be used for the injection. Preferably, urea, in particular aqueous urea, is injected. The injected urea is converted into ammonia within the exhaust passage by a dissociation process. The dynamic conversion of urea to ammonia depends on the heat present in the exhaust gas within the loop portion. As a result of the mixing of (cold) urea with the exhaust gas, the (local and instantaneous) temperature of the exhaust gas (Ta, Tr) downstream of the urea injector ( 16) can be reduced.If the (local and instantaneous) temperature of the exhaust gas Ta, Tr) downstream of the reductant injector (16) is too low, dissociation may be insufficient resulting in droplets of non-dissociated urea adhering to any surfaces of the exhaust passage (12).According to a preferred embodiment, the addition of a reducing agent, in particular urea, is carried out or prevented based on the determined temperature (T, Ta, Tr) and / or based on the instantaneous flow direction (BD, RD) of the exhaust gas through the loop section (13).According to a first aspect, the reducing agent may be injected during a time period (25) in which the switching valve (17) is in a certain switching position for guiding the exhaust gas in the basic direction (BD) and in which the detected temperature (T, Ta, Tr) is equal to or higher than the reduction active minimum temperature (T2). Such a time period is usually present immediately after the second switching event (31). In this time period ( 25), it is ensured that the (local and instantaneous) exhaust gas temperature (Ta, Tr) downstream of the reducing agent injector ( 16) is high enough for rapid and complete dissociation of the injected reducing agent, in particular urea. Consequently, the injected urea can be directly and completely stored within the reducing agent catalyst (15), and an effective conversion of NOx can be achieved almost immediately after the start of injections. As can be seen from FIG. 5, reductant injections ( 32) may be performed with a high injection amount or injection rate immediately after the second switching event ( 31). As a result, a storage target value for ammonia ( 33) can be reached very quickly, resulting in complete NOx conversion efficiency.The predefined tolerance value is preferably selected such that the cooling effect caused by the reducing agent injection and the cooling effect caused by heat loss after the second changeover event ( 31) cause a subsequent temperature drop which is equal to or less than the tolerance value, i.e. such that the (local and instantaneous) exhaust gas temperature (Tr) at or in the reducing agent catalytic converter ( 15) remains active minimum temperature (T 2) or within the reduction temperature window ( 28) above the reduction.According to another aspect, the injection of a reducing agent is preferably prevented during a period (23, 24) in which the switching valve (17) is in a specific switching position, in which the exhaust gas is conducted in the opposite direction (RD), or in which the detected temperature (T, Ta, Tr) is lower than the reduction active minimum temperature (T2). Such a period of time is normally present in a first time phase ( 23) before the first switching event ( 30) and in a second time phase ( 24) between the first switching event ( 30) and the second switching event ( 31).At the first time phase (23), the (local and instantaneous) exhaust temperature (Ta, Tr) downstream of the reducing agent injector (16) may be insufficient to allow rapid or complete dissociation of the injected reducing agent. By means of the described prevention of injections of reducing agent, it is achieved that droplets of the reducing agent remain adhering to any surface within the exhaust gas passage (12), which could have negative effects on the exhaust gas after-treatment device (11) and its components.Because of the opposite direction (RD), in the second time phase, any injected reductant would be introduced into the adsorption catalyst (14) instead of the reductant catalyst, which would be a waste of reductant because the selective catalyst reaction using the reductant cannot be performed within the NOx adsorption catalyst (14). By means of the described prevention of injections of reducing agent, such waste of reducing agent is avoided.The reducing agent injector (16) is preferably disposed close to or immediately behind the NOx adsorption catalyst (14) with respect to the base direction (BD). This maximizes the transport distance of the injected reductant prior to reaching the reductant catalyst. A long transport distance may help the dissociation process to be performed completely and the ammonia may be mixed evenly with the exhaust gas, which increases both reductant storage and conversion within the reductant catalyst and thus conversion efficiency.Modifications of the invention are possible in various ways. In particular, the features described, shown or claimed for the respective exemplary embodiments can be combined, interchanged or omitted in any desired manner.The internal combustion engine (10) is preferably a diesel engine. The exhaust after treatment device (11) may include a valve actuator (22) controlled according to the command values (26, 27, 26') output from the controller (20). At least one temperature sensor (21, 21') can be contained in the exhaust gas aftertreatment device (11), which can be arranged in particular on or within the switching valve (17) or on or within the loop section (13). In particular, a temperature sensor (21') can be arranged at each end of the loop section, preferably in the vicinity of or directly at the inflow region of the respective catalytic converter (14, 15) into which the exhaust gas flows.The reducing agent injector ( 16) can be supplied with a reducing agent from a reducing agent reservoir ( 34) by a pump ( 35).The term "reducing agent" may likewise include a reactant that may be directly involved in a chemical reaction with NOxand / or a precursor that is converted to the reactant prior to the chemical reaction with NOx. The reactant may be ammonia or any other suitable chemical substance. The precursor may be urea, in particular an aqueous solution containing urea, or any other suitable chemical substance. Urea can be injected into the exhaust gas and converted there into ammonia.LIST OF REFERENCE CHARACTERS10An internal combustion engine is an internal combustion engineInternal combustion engine11Exhaust Gas After-Treatment DeviceExhaust gas aftertreat device12Exhaust PassageExhaust gas passage13Loop PortionLoop section section14Adsorption catalystAdsorption catalyst / PNA15Reducing Agent CatalystReactant catalyst / SCR16Reducing agent injector / urea injector / reducing agent addition controlReactant injector / Urea injector / Reactant injector controller17On-off valveSwitching Valve18Exhaust Gas InflowExhaust gas inflow19Exhaust Gas OutflowExhaust gas outflow20Control UnitController21, 21'Temperature sensorTemperature sensor22Valve actuatorValve actuator23Shift Phase 1Switching phase 124Switching Phase 2Switching phase 225Switching phase 3Switching phase 326, 26'Normal Flow CommandBasic direction command27Countercurrent commandReversed direction command28Reduction Temperature WindowReduction temperature window window29Adsorption Temperature WindowAdsorption temperature window30First Switching EventFirst switching event31Second Switching EventSecond switching event32Instantaneous urea addition quantity / instantaneous ammonia storage quantityTemporary urea injection quantity / Temporary ammonia storage mount33Storage Set Point for AmmoniaStorage target of Ammonia34Reducing agent reservoirReactant Reservoir35Pump PumpPump Pump36Intermediate Temperature Interval / Temperature GapIntermediate temperature interval / temperature gapSVPCommand for Switching Valve PositionSwitching Valve Position CommandT. TTemperature: TemperatureTemperatureT. TTime TimeTime TimeNH3Ammonia Storage Amount / Urea Addition AmountAmmonia storage mount / Urea injection mountT1Adsorption active maximum temperature / first limit valueAdsorption active maximum temperature / first thresholdT2Reduction Active Minimum TemperatureReduction active minimum temperatureT3Switching Threshold Value / Second Limit ValueSwitching threshold / second thresholdTa, Ta'Adsorption catalyst temperature / Exhaust Gas Temperature on the Adsorption Catalyst with and without Gas Flow ReversalTemperature of adsorption catalyst / exhaust gas temperature at adsorption catalyst with and with out gas flow redectionTr, Tr'Reducing agent catalyst temperature / exhaust gas temperature at reducing agent catalyst with and without gas flow reversalTemperature of reactant catalyst / exhaust gas temperature at reactant catalyst with and with out gas flow redidectionBDBase DirectionBasic DirectionRDOpposite directionReversed direction

Claims

Method for carrying out an exhaust gas aftertreatment in an exhaust gas aftertreatment device (11) comprising an exhaust gas passage (12), an adsorption catalyst (14) and a reducing agent catalyst (15), wherein the adsorption catalyst (14) and the reducing agent catalyst (15) are arranged in a loop section (13) of the exhaust gas passage (12), characterized in that the method comprises the following steps: - determining an exhaust gas temperature (T); reversing the flow direction of the exhaust gas within the loop section (13) based on the detected temperature from a base direction (BD) passing from the adsorption catalyst (14) through the reducing agent catalyst (15) to a reverse direction (RD) passing from the reducing agent catalyst (15) through the adsorption catalyst (14) when the detected temperature (T, Ta) exceeds a first threshold value corresponding to an active adsorption maximum temperature (T1).Method according to one of the preceding claims, wherein the exhaust gas is reversed from the opposite direction (RD) to the base direction (BD) based on the determined temperature (T, Tr), in particular if the determined temperature (T, Tr) exceeds a second threshold value (T3).Method according to Claim 2, wherein the second threshold value (T3) is higher than a reduction active minimum temperature (T2) by a predefined tolerance value.Method according to one of the preceding claims, wherein a reversal of the exhaust gas flow is controlled by a control unit (20) on the basis of the detected temperature (T, Ta, Tr), in particular wherein a switching valve (17) is actuated by the control unit (20) on the basis of a command value (26, 26', 27).Method according to claim 1 or any of the preceding claims, wherein based on the determined temperature (T, Ta, Tr) the injection of a reducing agent, in particular urea, is carried out or prevented.Method according to Claim 5, wherein - the reducing agent is injected into the exhaust gas, in particular between the adsorption catalyst (14) and the reducing agent catalyst (15) within the loop section (13) of the exhaust gas passage (12), during a period in which the switching valve (17) is in a specific switching position for guiding the exhaust gas in the basic direction (BD) and in which the detected temperature (T, Ta, Tr) is equal to or higher than the reduction active minimum temperature. (T2); AND / OR wherein - the injection of the reducing agent is prevented during a period in which the switching valve (17) is in a specific switching position for guiding the exhaust gas in the opposite direction (RD) or in which the detected temperature (T, Ta, Tr) is lower than the reduction active minimum temperature (T2).A software product comprising instructions for executing a method according to any of claims 1-6.Electronic control unit for controlling an exhaust gas aftertreatment device (11), wherein the control device is designed to carry out a method according to one of Claims 1-6.An exhaust gas after-treatment device comprising - an exhaust passage (12), - an adsorption catalyst (14) for storing nitrogen oxides (NOx), and a reducing agent catalyst (15) for selectively reducing NOx with a reducing agent; characterized in that - the exhaust passage (12) comprises a loop portion (13); and wherein - the adsorption catalyst (14) and the reducing agent catalyst (15) are disposed in the loop portion (13) of the exhaust passage (12); and wherein - the exhaust gas after-treatment device (11) comprises a switching valve (17) for controlling the inflow (18) and outflow (19) of the exhaust gas to and from the loop portion (13); and wherein - the switching valve (17) is configured to reverse the exhaust flow through the loop portion (13), and wherein - the adsorption catalyst (14) and the reducing agent catalyst (15) are configured such that an effective adsorption of NOx and an effective reduction of NOx cover different temperature ranges separated by an intermediate temperature interval (36).The exhaust gas aftertreatment device according to claim 9, wherein the adsorption catalyst (14) and the reducing agent catalyst (15) are configured such that an effective adsorption of NOx in the adsorption catalyst (14) is active within an adsorption temperature window (29) that is actively bounded upward by an adsorption of maximum temperature (T1) and an effective reduction of NOx in the reducing agent catalyst (15) is active within a reduction temperature window (28) that is actively bounded downward by a reduction of minimum temperature (T2); and wherein the temperature windows (28, 29) cover different temperature ranges separated by an intermediate temperature interval (36).Exhaust gas aftertreatment device according to Claim 9 or 10, comprising: - a temperature determination means for determining a present temperature (T) within the exhaust gas aftertreatment system, in particular an exhaust gas temperature (Ta, Ta') at the adsorption catalytic converter (14) and / or an exhaust gas temperature (Tr, Tr') at the reducing agent catalytic converter (15).Exhaust gas aftertreatment device according to one of Claims 9 to 11, comprising a control unit (20) which is designed to carry out an exhaust gas aftertreatment method according to one of Claims 1 to 6.

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