DE102014226659A1 - A method of operating a methane oxidation catalyst and exhaust aftertreatment system - Google Patents

Abstract

In a method of operating a methane oxidation catalyst (13) in an exhaust aftertreatment system of an internal combustion engine (10), the methane oxidation catalyst is exposed to a gas composition reactivating to the methane oxidation catalyst, thereby increasing the activity of the methane oxidation catalyst.

Description

The present invention relates to a method of operating a methane oxidation catalyst in an exhaust aftertreatment system of an internal combustion engine and an exhaust aftertreatment system comprising at least one methane oxidation catalyst.

State of the art

Internal combustion engines are known which can be operated both with a methane-containing gas, for example natural gas or methane, and with a mixture of gas and another fuel, for example diesel fuel.

Pure gas engines are often derived from gasoline or diesel engines, where usually a spark ignition to ignite the gas / air mixture is carried out using spark plugs. In diesel / gas engines, the engine is basically based on a diesel engine that allows both pure diesel operation and mixed operation with diesel fuel and gas. Here, part of the diesel heating value is replaced by gas. The ignition of the entire fuel, so the diesel gas / air mixture, via the diesel component. In this case, substitution rates of the diesel fuel by gas of up to 70% are possible.

In all approaches based at least in part on the combustion of methane-containing gas, the problem of high, raw-engine methane emissions occurs. Especially for reasons of climate protection, the methane emissions must be reduced as part of an exhaust aftertreatment. Methane oxidation catalysts (MOCs) are known which oxidize the methane contained in the exhaust gas on the basis of palladium-rich formulations. For this purpose, it is possible to use formulations which have a weight ratio of palladium (Pd) to platinum (Pt) of up to, for example, 7: 1 or even greater. Other methane oxidation catalysts are based on so-called palladium-only formulations, e.g. Pd / alumina. In general, with such formulations, however, only a certain methane conversion can be observed above 400 ° Celsius. For complete oxidation often temperatures of well over 500 ° C are necessary.

It is known that methane oxidation catalysts, in particular palladium-rich methane oxidation catalysts, are extremely sensitive to sulfur and already after a short runtime with sulfur-containing gas or diesel show a dramatic deterioration of their oxidation effect. However, even in the absence of sulfur, a creeping decline in methane oxidation activity is observed in lean exhaust gas in palladium-rich catalysts, and especially in palladium-only formulations ( M. Lyubovsky, M. and Pfefferle, L .; Catalysis Today 47 (1999); Pages 29-44 ). Furthermore, an oscillatory behavior of palladium-rich catalysts is described ( R. Schwidernoch; Dissertation University of Heidelberg; 2005 ).

The German translation DE 11 2011 104 327 T5 An international patent application relates to an exhaust system with a diesel oxidation catalyst. Upstream of the diesel oxidation catalyst, an injector for fuel is provided so that salvoes of a fuel can be injected directly into the exhaust line. By contact of the injected hydrocarbons with an oxide layer of the diesel oxidation catalyst, a regenerating effect can be achieved.

Disclosure of the invention

Advantages of the invention

The invention provides a method of operating a methane oxidation catalyst in an exhaust aftertreatment system of an internal combustion engine. According to the invention, the methane oxidation catalyst is exposed to a gas composition which reactivates to the methane oxidation catalyst. As a result, an increase in activity of the methane oxidation catalyst is achieved. With this measure, a creeping oxidation activity loss of a methane oxidation catalyst can be reduced or completely avoided during its runtime. In this way, it is ensured that a methane oxidation catalyst retains sufficient methane oxidation activity even with a longer transit time, so that an optimal exhaust aftertreatment with regard to the methane oxidation is ensured. In a particularly advantageous manner, the inventive method for exhaust aftertreatment systems of internal combustion engines to use that produce predominantly lean exhaust gases and at least partially burn methane, ie in particular gas engines or diesel / gas engines. Especially these engines or internal combustion engines usually produce high raw-engine methane emissions, which must be reduced in the course of exhaust aftertreatment. The internal combustion engine operation with an excess of air, ie at λ> 1 (lean operation), generally does not allow optimal operation of a methane oxidation catalyst, since the required high temperatures for the methane oxidation are not usually achieved. Therefore, it is of particular importance to counteract a gradual deactivation of the methane oxidation catalyst. This allows the process according to the invention by the methane oxidation catalyst of a reactivating gas composition is suspended. It is particularly advantageous here if the methane oxidation catalyst is periodically exposed to the reactivating gas composition. In this case, it may be provided, for example, that after a certain period of lean operation, the methane oxidation catalyst is exposed to the reactivating gas composition for a certain period of time, in particular for a short period of time described in more detail below. By "periodic" is meant that the reactivating gas composition is preferably periodically repeated, for example, the reactivating gas composition may be generated after each lean operating phase or each time a certain period of lean operation phase of the internal combustion engine. The duration of the regular lean operation of the internal combustion engine before the reactivation of the methane oxidation catalyst according to the invention can be variable. A reactivation of the methane oxidation catalyst according to the process of the invention can be carried out regularly or else as needed.

In particular, the reactivating gas composition has a reducing or oxidizing effect on the formulation or the material of the methane oxidation catalyst. As a result, for example, palladium oxide present in the catalyst can be at least partially reduced again to metallic palladium, as a result of which the oxidation activity of the methane oxidation catalyst can be markedly increased. Palladium oxide forms in the course of the service life of a suitably equipped methane oxidation catalyst, in particular in a lean operation of the internal combustion engine. This palladium dioxide may be located on the surface of the corresponding noble metal particles of a methane oxidation catalyst or else in the bulk material of the palladium of the methane oxidation catalyst. This formation of palladium oxide is reversed by the particular periodically generated reactivating gas composition in the exhaust gas line.

In a first embodiment of the method according to the invention, the reactivating gas composition is generated by an engine internal rich operation of the internal combustion engine, wherein in this embodiment of the method according to the invention, the gas composition causes reducing effect. The rich operation is preferably performed for a short period of time and periodically recurring. For example, after a lean burn operation of the engine (lean time) lasting minutes or hours, the methane oxidation catalyst may be exposed to a rich, all-reducing exhaust gas composition for a few seconds, which exhaust gas composition is caused by the brief in-engine rich operation. The engine internal rich operation may be performed, for example, for a period of about 5 to 60 seconds. The internal engine rich operation can be carried out in particular in the context of accumulated fat operation by fat / lean switching, for example, the rich operation is maintained for about 10 seconds, but then again switched for a limited time of a few seconds to lean operation. This rich / lean changeover is performed a few times, so that, in sum, for example, there is an accumulated rich operating time of up to 60 seconds. This mode of operation has the advantage that the pollutant emissions (in particular hydrocarbons and carbon monoxide) downstream of the catalyst are not too high and / or the temperatures do not become too high. The internal engine rich operation can be effected, for example, by a late post-injection with diesel as an engine internal measure.

In another embodiment of the method according to the invention, the reactivating gas composition is generated by injecting fuel into the exhaust aftertreatment system, ie directly into the exhaust gas line. In particular, the fuel is injected upstream of the methane oxidation catalyst, wherein the fuel injection may take place immediately before the methane oxidation catalyst or further upstream. This basic embodiment of the method is particularly advantageous in those internal combustion engine systems which are not designed for the temperature loads associated with a rich operation. This is true, for example, for gas engines derived from a diesel engine. In such engines or internal combustion engines even a brief rich operation would possibly lead to an excessive load, in particular a temperature load, the engine components, such as a turbocharger. In order to prevent damage to the engine components by excessively high temperatures, it is advantageous to effect the gas composition reactivating the methane oxidation catalyst by injecting fuel into the exhaust aftertreatment system. For carrying out the method according to the invention, one or more fuel injectors in the exhaust gas line are required for this embodiment of the method. For the generation of a reactivating gas composition, it is generally sufficient if the injection of fuel into the exhaust system takes place only during a very short period after a lean operation of the internal combustion engine. In this case, a few milliseconds of fuel injection duration may be sufficient, for example between 20 and 500 ms. For example, if the injection frequency is in the range of about 1 Hz or is less, a fuel injection period of a few seconds is appropriate. The fuel injection according to the inventive method is preferably carried out in those phases in which the exhaust gas temperature is above about 350 ° C. This measure has the advantage that it is ensured at these relatively high temperatures that the injected fuel completely evaporated and it does not come to a local sooting in the catalyst.

The injection of fuel directly into the exhaust line is preferably carried out in a multi-stage process, wherein initially the oxygen mass flow of the exhaust gas is reduced by engine measures, before the fuel is injected into the exhaust aftertreatment system. These engine measures for reducing the mass flow of oxygen may include, for example, a throttling of the fuel supply or a lambda reduction. To burn off the remaining oxygen in the exhaust gas, so much fuel is then metered in upstream of the methane oxidation catalyst until a net reducing exhaust gas composition in the region of the methane oxidation catalyst is achieved.

In a further embodiment of the method according to the invention, the reactivating gas composition is also generated by the injection of fuel into the exhaust aftertreatment system. However, the fuel is injected into the exhaust system in such a way that temperatures of 700 ° C. or more, or even temperatures of more than 800 ° C. are reached. These high temperatures are preferably maintained for several minutes, for example for 2 to 10 minutes. At these high temperatures, to which the methane oxidation catalyst is exposed, for example, for a few minutes, the palladium oxide of the methane oxidation catalyst formed in lean operation is at least partially decomposed to metallic palladium, whereby the oxidation activity of the methane oxidation catalyst can be significantly increased again. Preferably, in this embodiment, so much fuel (fuel) is metered in upstream of the methane oxidation catalyst until under still lean conditions by burning off a portion of the residual oxygen in the methane oxidation catalyst temperatures of more than 700 ° C or more than 800 ° C. prevail. Thus, these are still lean conditions, thus acting as a whole oxidizing, whereby the methane oxidation catalyst can be converted back into its activated state catalyst. These high temperatures are preferably generated for a few minutes in the methane oxidation catalyst, for example, for a period of between about 1 to 10 minutes. A particular advantage of this embodiment of the method is that due to the very high temperatures in the methane oxidation catalyst, a large part of the sulfur optionally added in the methane oxidation catalyst is expelled in the form of sulfur oxide. Also by this effect, a regenerative effect on the methane oxidation catalyst is achieved.

In the embodiment of the method according to the invention, in which temperatures of 700 ° C. or more are achieved by injecting fuel into the exhaust gas line, lean (oxidizing) conditions are set net. In the above-explained embodiment of the method, in which net reducing conditions are set by an internal engine rich operation or by fuel injections into the exhaust gas line, significantly lower temperatures between about 350 to 500 ° C. are generally sufficient for a reactivation of the methane oxidation catalyst.

The fuel to be metered directly into the exhaust gas line is, for example, the same fuel that is also used for the operation of the internal combustion engine. In the case of pure gas engines, this can be, for example, natural gas. However, it is particularly preferred that at least proportionately a liquid fuel for the purposes of the inventive method is injected into the exhaust system, such as diesel or gasoline, or a mixture of a liquid fuel with a gaseous fuel. This also applies to pure gas engines. This has the advantage that as a result of the injection of an at least partially liquid fuel, the reactivity of such a fuel mixture is generally higher than with pure gas, since methane as a constituent of this gas is generally very inert. In a pure gas engine, which is set up for diesel injection into the combustion chamber for ignition, it is also possible, for example, to inject diesel into the exhaust gas line for carrying out the method according to the invention. Alternatively, for example, gasoline can be used. In pure gas engines in which a total of no injection of liquid fuel is provided for internal combustion engine operation, an additional tank may be provided for the purposes of the method according to the invention, which contains the liquid fuel which is metered into the exhaust line in the course of the inventive method, ie For example, a tank for gasoline or diesel, which is assigned to the exhaust aftertreatment system. For dual-fuel engines or diesel-fueled gas engines, diesel is preferably used for post-engine fuel injection into the exhaust line. The use of diesel for these purposes is generally particularly advantageous because the light-off temperature for diesel at the methane oxidation catalyst is around 300 ° C is significantly lower than the light-off temperature of the methane oxidation catalyst when operated with methane (light-off temperature about 450 to 550 ° C).

The invention further includes an exhaust aftertreatment system for an internal combustion engine, wherein the exhaust aftertreatment system comprises at least one methane oxidation catalyst. According to the invention, at least one fuel injection device is provided upstream of the at least one methane oxidation catalyst. This system is particularly suitable for carrying out the method described above, wherein the methane oxidation catalyst is subjected to a reactivating gas composition by a periodic, short-term injection of fuel into the exhaust line, thereby causing a regeneration or increase in activity of the methane oxidation catalyst. As a result, a creeping loss of activity of the methane oxidation catalyst can be effectively counteracted.

The methane oxidation catalyst used is preferably a methane oxidation catalyst, in the formulation of which palladium forms the main constituent. The formulation may, for example, have a dominant palladium mass fraction and minor platinum and / or rhodium moieties. As a carrier material of the methane oxidation catalyst, in particular, a ceramic material is suitable, e.g. Alumina or mixed oxides, e.g. Barium titanate. The methane oxidation catalyst may also contain a palladium-only formulation.

In a particularly preferred embodiment, the methane oxidation catalyst contains at least one oxygen-storing material, in particular a zirconium oxide and / or a lanthanum oxide and / or a cerium oxide and / or a praseodymium oxide and / or a neodymium oxide or mixtures thereof. The oxygen-storing material can therefore be based in particular on zirconium oxides and / or lanthanum oxides and / or cerium oxides and / or praseodymium oxides and / or neodymium oxides or mixtures thereof. The storage of oxygen in the methane oxidation catalyst associated with such material prevents or at least reduces breakthroughs of hydrocarbons on the methane oxidation catalyst. Therefore, the use of such a designed methane oxidation catalyst is particularly advantageous when according to the inventive method fuel upstream, especially immediately upstream of the methane oxidation catalyst is injected into the exhaust system and a total fat, so reducing exhaust gas composition is set periodically on methane oxidation catalyst.

In a further embodiment of the exhaust aftertreatment system according to the invention, the exhaust aftertreatment system is assigned at least one tank for a liquid fuel, in particular for diesel or gasoline. In such a tank, the liquid fuel is provided, which is provided for the post-engine injection of fuel into the exhaust system according to a preferred embodiment of the method according to the invention. Such a tank is particularly useful in systems with a pure gas engine, where no Dieselinjektion example, provided in the combustion chamber of the internal combustion engine for ignition.

In a further embodiment of the exhaust gas aftertreatment system according to the invention, the exhaust aftertreatment system further comprises a sulfur adsorption device. This sulfur adsorption device may be located upstream of the methane oxidation catalyst. Alternatively, the sulfur adsorption device may also be integrated into the methane oxidation catalyst. The Schwefeladsorptionseinrichtung acts as a sulfur trap, which avoids a caused by sulfur in the exhaust deterioration of the effectiveness of a palladium-containing methane oxidation catalyst. The sulfur adsorption device may in particular be a sulfur oxide adsorption device, preferably a sulfur oxide storage device. For example, the material for the sulfur oxide storage device may be based on a magnesium aluminate spinel. Furthermore, the formulation of the sulfur adsorption device may be based on a conventional full formulation for a nitrogen oxide storage catalyst.

The inventive method and the exhaust aftertreatment system according to the invention are particularly suitable for pure gas engines or diesel / gas engines, which are at least temporarily with excess air, ie at λ> 1, operated and at least partially with a methane-containing gas or with a mixture of a methane-containing gas and, for example, diesel (dual-fuel) are operated. In addition to these lean-running gas or diesel / gas engines, the method according to the invention and the exhaust gas aftertreatment system according to the invention are in principle also suitable for other internal combustion engines, for example for a conventional diesel engine, for exhaust aftertreatment.

The invention further comprises a computer program which is set up to carry out the described method. Furthermore, the invention comprises a machine-readable storage medium on which the computer program described is stored, as well as an electronic Control device which is set up for carrying out the method according to the invention. The implementation of the method according to the invention as a computer program or as a control program has the advantage that even existing systems, for example motor vehicles, can be set up in a simple manner for carrying out the method according to the invention, provided the systems are equipped with the corresponding components in the exhaust aftertreatment system.

Further features and advantages of the invention will become apparent from the following description of embodiments in conjunction with the drawings. In this case, the individual features can be implemented individually or in combination with each other.

Brief description of the figures

In the drawings show:

1 schematic representation of components of an exhaust aftertreatment system according to the invention for an internal combustion engine;

2 schematic representation of components of another embodiment of an exhaust aftertreatment system according to the invention;

3 schematic representation of components of another embodiment of an exhaust aftertreatment system according to the invention and

4 schematic representation of components of another embodiment of an exhaust aftertreatment system according to the invention.

Description of exemplary embodiments

1 shows in a schematic way the arrangement of components of an exhaust aftertreatment system according to the invention, in the exhaust system of an internal combustion engine 10 are provided. In the internal combustion engine 10 it is in particular a lean-running gas engine or diesel / gas engine, which can be operated with a mixture of gas and diesel. To increase the performance of the internal combustion engine 10 is the internal combustion engine 10 a turbocharger 11 assigned. The exhaust gases of the internal combustion engine 10 be in the exhaust system initially by a Schwefeladsorptionseinrichtung 12 guided. Downstream of the sulfur adsorption device 12 is a methane oxidation catalyst 13 arranged in the methane oxidation catalyst 13 an oxidation of the methane contained in the exhaust gas takes place. By the upstream sulfur adsorption 12 is achieved that the function of the methane oxidation is not affected or deteriorated by sulfur-containing components in the exhaust gas. The system further includes an SCR catalyst 16 to reduce the mass fraction of the nitrogen oxides contained in the exhaust gas. That for the catalytic reaction within the SCR catalyst 16 Required reactants, such as liquid urea water solution, are passed upstream of the SCR catalyst 16 arranged metering point 15 sprayed into the exhaust system. This example of an exhaust aftertreatment system further includes a catalytic particulate filter 14 on the upstream of the SCR catalyst 16 is arranged.

Upstream of the methane oxidation catalyst 13 and simultaneously upstream of the sulfur adsorption device 12 is a fuel injector 17 arranged. Using the injector 17 be made according to the inventive method periodic fuel injections directly into the exhaust system. With these fuel injections are in the range of methane oxidation catalyst 13 Generates conditions that reactivating or regenerating the methane oxidation catalyst 13 Act. In particular, a reducing or oxidizing gas composition can be provided which involves a reduction or decomposition of palladium oxide which occurs over the service life of the methane oxidation catalyst 13 has formed, causing the oxidation activity of the methane oxidation catalyst 13 can be restored. Alternatively, it is possible to dispense with a fuel injector, wherein the reactivating gas composition in the region of the methane oxidation catalyst is generated by internal engine measures.

The periodic, ie recurring, setting of a reactivating gas composition can be brought about after a few minutes to a few 10 hours of lean operation. For the reactivating gas composition, in particular a net reducing, that is slightly rich (λ <1, but close to 1) exhaust gas composition can be brought about in order to keep the methane oxidation catalyst in a partially reducing and thus activated catalyst state. In this case, it is usually sufficient if the rich, net reducing exhaust gas composition is held for a few seconds. A fuel injection into the exhaust gas line carried out for this purpose can take place, for example, for a few milliseconds, for example in the range between 20 and 500 ms. The duration of the lean-phase operation, that is, the normal operation of the system, can be made dependent on the extent of oxidative deactivation of the methane oxidation catalyst. The lean phase duration can be, for example, in the range of minutes to a few hours. In the regeneration of the Methane oxidation catalyst by internal engine measures, ie by a brief rich operation of the internal combustion engine, the lean phase duration may optionally include a longer period. Shorter periods, which are particularly useful in a regeneration on the basis of fuel injections into the exhaust system, have the advantage that the average methane oxidation efficiency of the methane oxidation catalyst is higher in the result than in the other variant with longer periods.

In one embodiment of the method according to the invention, the fuel injection can be carried out so that periodically after a lean time by fuel injections into the exhaust system very high temperatures in the methane oxidation catalyst 13 be achieved, ie in particular temperatures of higher than 700 ° C or higher than 800 ° C. These high temperatures are preferably maintained for a few minutes using the methane oxidation catalyst 13 formed palladium oxide is at least partially decomposed to metallic palladium, whereby the oxidation activity of the methane oxidation catalyst is restored. In this embodiment, so much fuel is metered into the exhaust line until, under still lean conditions, by burning off a portion of the remaining oxygen, these high temperatures are set in the methane oxidation catalyst. In the periodic fuel injection to produce very high temperatures in the lean exhaust gas thereby net oxidizing conditions are generated on the methane oxidation catalyst, whereby the methane oxidation catalyst is converted back to its activated state catalyst.

2 shows schematically a similar system as 1 In this embodiment, the sulfur adsorption device into the methane oxidation catalyst 23 is integrated. In detail, the internal combustion engine 20 a turbocharger 21 assigned. The exhaust gases of the internal combustion engine 20 be in the exhaust system through the combined catalyst device 23 which represents a methane oxidation catalyst with integrated sulfur adsorption, in a sense with integrated sulfur trap. After methane oxidation, the exhaust gas passes through a catalytic particulate filter 24 before there is an SCR catalyst 26 is supplied. Upstream of the SCR catalyst 26 is a metering point 25 provided for the reagent solution, which for the catalytic processes in the SCR catalyst 26 is required. Upstream of the methane oxidation catalyst 23 with integrated sulfur trap is an injection device 27 arranged for fuel.

The embodiment of the exhaust aftertreatment system with a sulfur adsorption 12 ( 1 ) or with a methane oxidation catalyst 23 with integrated sulfur adsorption device ( 2 ) has particular advantages for the periodic rich operation according to the invention on the methane oxidation catalyst. The sulfur in the sulfur adsorption device 12 or the methane oxidation catalyst 23 is so tightly bound that in a short term "cold" rich gas atmosphere having a temperature below 500 to 550 ° C, no interfering palladium sulfide can be formed. If no sulfur adsorption device were present, it would be expected that the methane oxidation catalyst would have at least some fraction of bound sulfur oxides, eg in the form of palladium sulfate, which would then eventually be converted to palladium sulfide. This would be detrimental to the activity of the methane oxidation catalyst.

By means of a sulfur adsorption device in the exhaust gas line, the frequency of the methane oxidation catalyst reactivation according to the invention can be reduced since an additional activity deterioration, independent of palladium oxide formation, due to sulfur-containing components in the exhaust gas is prevented.

Desulphurisation required for regeneration of a sulfur adsorption device is generally energy and temperature intensive. In the systems illustrated here, such desulfurization takes place independently of the periodic "cold" enrichment according to the invention. The enrichment according to the invention serves exclusively for the non-sulfur-related reactivation of the methane oxidation catalyst.

In another embodiment of the exhaust aftertreatment system, a coated particulate filter and an SCR catalyst can be combined in one component as a so-called "SCR on filter" (also SCRoF: "SCR on filter"). Such embodiments are in the 3 and 4 illustrated. This shows 3 a system with a methane oxidation catalyst 33 to which a sulfur adsorption device 32 upstream. 4 shows a system in which the sulfur adsorption in the methane oxidation catalyst 43 is integrated. Comparable with the systems 1 and 2 is the internal combustion engine 30 respectively. 40 , So in particular a lean-running gas engine or a lean-running diesel / gas engine, a turbocharger 31 respectively. 41 assigned. Referring to 3 go through the exhaust gases of the internal combustion engine 30 the sulfur adsorption device 32 before entering the methane oxidation catalyst 33 reach. Downstream of the methane oxidation catalyst 33 is the part ("SCR on filter") 36 arranged, which integrates an SCR catalyst on a filter. Upstream of the "SCR on filter" 36 there is a metering point 35 for the liquid reagent used for the catalytic reaction in the "SCR on filter" 36 is required. Referring to 4 go through the exhaust gases of the internal combustion engine 40 the methane oxidation catalyst 43 with integrated sulfur adsorption device. The exhaust gases then pass through the "SCR on filter" 46 where upstream of the "SCR on filter" 46 a metering point 45 for the liquid reagent used for the catalytic reaction in the "SCR on filter" 46 is required, is provided. Upstream of the sulfur adsorption device 32 and simultaneously upstream of the methane oxidation catalyst 33 ( 3 ) or upstream of the methane oxidation catalyst 43 with integrated sulfur adsorption is in each case a fuel injector 37 respectively. 47 intended. These systems are also suitable for carrying out the method according to the invention, in which periodically after a lean operation of the internal combustion engine 30 respectively. 40 Fuel is injected to the methane oxidation catalyst 33 respectively. 43 to produce a gas composition reactivating to the methane oxidation catalyst 33 respectively. 43 acts.

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 112011104327 T5 [0006]

Cited non-patent literature

• M. Lyubovsky, M. and Pfefferle, L .; Catalysis Today 47 (1999); Pages 29-44 [0005]
• R. Schwidernoch; Dissertation University of Heidelberg; 2005 [0005]

Claims (15)

Method for operating a methane oxidation catalyst ( 13 ; 23 ; 33 ; 43 ) in an exhaust aftertreatment system of an internal combustion engine ( 10 ; 20 ; 30 ; 40 ), characterized in that to increase the activity of the methane oxidation catalyst, the methane oxidation catalyst ( 13 ; 23 ; 33 ; 43 ) is exposed to a gas composition reactivating to the methane oxidation catalyst. Process according to claim 1, characterized in that the methane oxidation catalyst ( 13 ; 23 ; 33 ; 43 ) is periodically exposed to the reactivating gas composition. A method according to claim 1 or claim 2, characterized in that the gas composition has a reducing or oxidizing effect. Method according to one of the preceding claims, characterized in that the reactivating gas composition by an internal engine rich operation of the internal combustion engine ( 10 ; 20 ; 30 ; 40 ) is produced. Method according to one of claims 1 to 3, characterized in that the reactivating gas composition is generated by injection of fuel into the exhaust aftertreatment system, wherein the fuel upstream of the methane oxidation catalyst ( 13 ; 23 ; 33 ; 43 ) is injected. A method according to claim 5, characterized in that in a multi-stage process, the oxygen mass flow of the exhaust gas is reduced by engine measures before fuel is injected into the exhaust aftertreatment system. A method according to claim 5 or claim 6, characterized in that by the injection of fuel into the exhaust aftertreatment system temperatures of 700 ° C or more in the region of the methane oxidation catalyst ( 13 ; 23 ; 33 ; 43 ) be generated. Method according to one of claims 5 to 7, characterized in that the injected fuel is a liquid fuel, in particular diesel or gasoline, or a mixture of a liquid fuel with a gaseous fuel. Exhaust after-treatment system for an internal combustion engine ( 10 ; 20 ; 30 ; 40 ), wherein the exhaust aftertreatment system at least one methane oxidation catalyst ( 13 ; 23 ; 33 ; 43 ), characterized in that upstream of the at least one methane oxidation catalyst at least one injection device ( 17 ; 27 ; 37 ; 47 ) is arranged for fuel. Exhaust after-treatment system according to claim 9, characterized in that the methane oxidation catalyst ( 13 ; 23 ; 33 ; 43 ) contains at least one oxygen-storing material, in particular a zirconium oxide and / or a lanthanum oxide and / or a cerium oxide and / or a praseodymium oxide and / or a neodymium oxide or mixtures thereof. Exhaust after-treatment system according to claim 9 or claim 10, characterized in that the exhaust aftertreatment system is assigned at least one tank for a liquid fuel, in particular for diesel or gasoline. Exhaust gas aftertreatment system according to one of claims 9 to 11, characterized in that the exhaust aftertreatment system further comprises a sulfur adsorption device ( 12 ; 32 ), wherein the sulfur adsorption device upstream of the methane oxidation catalyst ( 13 ; 33 ) or in the methane oxidation catalyst ( 23 ; 43 ) is integrated. Computer program adapted to perform the steps of a method according to one of claims 1 to 8. Machine-readable storage medium on which a computer program according to claim 13 is stored. An electronic control device adapted to perform the steps of a method according to any one of claims 1 to 8.

Images