DE102019129452A1 - Process for the aftertreatment of the exhaust gas of an internal combustion engine - Google Patents

Abstract

Method for aftertreatment of the exhaust gas of an internal combustion engine (1) which burns a gaseous fuel, namely a gas engine or a dual-fuel engine operated in the gas-fuel operating mode. The exhaust gas is routed over a CH4 oxidation catalytic converter (7) and an SCR reduction catalytic converter (8). As a reducing agent for the SCR reduction catalytic converter (8), NH3 or an NH3 precursor substance is introduced into the exhaust gas upstream of the CH4 oxidation catalytic converter (7).

Description

The invention relates to a method for the aftertreatment of the exhaust gas of an internal combustion engine that burns a gaseous fuel, namely a gas engine or a dual-fuel engine operated in the gas-fuel operating mode. The invention also relates to an internal combustion engine, namely a gas engine or dual-fuel engine.

In gas engines as well as in dual-fuel engines in the gas fuel operating mode, a gaseous fuel, such as natural gas, is burned. In such internal combustion engines that burn a gaseous fuel, incomplete combustion of the gaseous fuel can lead to undesirable emissions of CH ₄ (methane). Since methane is a strong greenhouse gas, the CH ₄ emissions into the environment must be kept as low as possible in internal combustion engines that burn a gaseous fuel.

It is already known from practice to pass the exhaust gas which leaves the cylinders of an internal combustion engine that burns a gaseous fuel over a CH ₄ oxidation catalyst in order to replace the CH _{4 in the CH 4 oxidation catalyst.} In internal combustion engines known from practice, the CH ₄ oxidation catalyst is used for CH ₄ oxidation and accordingly as catalytically active compounds with metals of the platinum group, in particular with platinum and / or with palladium. In internal combustion engines known from practice, the loading of the CH ₄ oxidation catalyst with a metal of the platinum metal group is typically more than 7 grams of platinum and / or palladium per liter of volume of the CH ₄ oxidation catalyst.

This causes high costs. Furthermore, the operating time of such CH ₄ oxidation catalysts known from practice is relatively short, since sulfur oxides which can get into the area of the CH ₄ oxidation catalyst can deactivate the catalytically active compounds of the platinum metal group. Therefore, in internal combustion engines known from practice, the possibility of reducing the CH ₄ emissions is limited.

From the DE 10 2015 001 495 A1 a method for operating an internal combustion engine is known in which a gaseous fuel is burned. Exhaust gas is passed over a CH ₄ oxidation catalyst. The CH ₄ oxidation catalyst has for CH ₄ oxidation as active components preferably cerium and / or cobalt and / or copper and / or iron, which are preferably in a zeolite matrix of the structures MOR, FER, PER, NFI, LTL, LAU, CHI or CHA are involved.

From the DE 10 2015 001 495 A1 it is also known that _{an SCR reduction catalyst is arranged downstream of the CH 4} oxidation catalyst, so that exhaust gas is passed over a CH ₄ oxidation catalyst and over an SCR reduction catalyst. A reducing agent for the SCR reduction catalyst, namely NH ₃ or an NH ₃ precursor substance, is _{introduced into the exhaust gas downstream of the CH 4} oxidation catalyst and upstream of the SCR reduction catalyst.

In order _{to sufficiently decompose the NH 3} precursor substance into NH ₃ and / or to atomize or distribute the reducing agent sufficiently finely and evenly in the exhaust gas, according to the DE 10 2015 001 495 A1 a relatively large distance between the CH ₄ oxidation catalyst and the SCR reduction catalyst is required. This leads to considerable disadvantages in terms of installation space.

Proceeding from this, the invention is based on the object of creating a novel method for aftertreatment of the exhaust gas of an internal combustion engine that burns a gaseous fuel and a corresponding internal combustion engine. This object is achieved by a method according to claim 1. The exhaust gas is passed over a CH ₄ oxidation catalytic converter and an SCR reduction catalytic converter.

The oxidation of CH ₄ takes place via NO ₂ CH ₄ + 2NO ₂ → CO ₂ + 2H ₂ O (Equation 1)

As a reducing agent for the SCR reduction catalyst, NH ₃ or an NH ₃ precursor substance is introduced into the exhaust gas upstream of the CH _{4 oxidation catalyst.} The reduction of nitrogen oxides on the SCR catalytic converter takes place according to the following equations 2NO + 2NH3 + 0.5O ₂ → N ₂ + 3H ₂ O (Equation 2) NO + NO ₂ + 2NH ₃ → N ₂ + H ₂ O (equation 3)

The invention therefore proposes that, during exhaust gas aftertreatment of the exhaust gas from an internal combustion engine which burns a gaseous fuel and whose exhaust gas is passed both over a CH ₄ oxidation catalyst and an SCR reduction catalyst, the NH ₃ or the NH ₃ precursor substance not downstream of the CH ₄ oxidation catalyst, but rather to be introduced into the exhaust gas _{upstream of the CH 4 oxidation catalyst.} This means that there is no need for a long mixing section between the CH ₄ oxidation catalyst and the SCR reduction catalyst. This allows installation space advantages to be realized. One executing the procedure The exhaust aftertreatment system can be made much more compact.

According to a first advantageous development of the invention, the exhaust gas is first passed over the CH ₄ oxidation catalyst and then over a separate SCR reduction catalyst, the NH ₃ or the NH ₃ precursor substance being introduced into the exhaust gas upstream of the CH _{4 oxidation catalyst.} According to this first development, the CH ₄ oxidation catalyst and the SCR reduction catalyst are designed as separate, separate catalysts. In this case, the CH ₄ oxidation catalyst is then preferably arranged upstream of the SCR reduction catalyst, the CH ₄ oxidation catalyst having negligible NH ₃ oxidation activity due to oxygen. In particular, it is provided that the CH ₄ oxidation catalyst does not contain any element of the platinum metal group in order to avoid the oxidation of the NH ₃ with the aid of O ₂ to N ₂ , NO, NO ₂ or N ₂ O.

According to an alternative, second and particularly preferred advantageous development of the invention, the exhaust gas is passed over a combined or integrated CH ₄ oxidation and SCR reduction catalytic converter. The NH ₃ or the NH ₃ precursor substance is introduced into the exhaust gas upstream of the combined or integrated CH ₄ oxidation and SCR reduction catalyst. The exhaust gas to be passed over the combined CH ₄ oxidation and SCR reduction catalytic converter preferably has an NO ₂ proportion, based on a total proportion of nitrogen oxides, of at least 25%, preferably of at least 35%, particularly preferably of at least 55% . In addition, it has proven to be advantageous if the NO ₂ proportion is at least 0.1 times the NO _x conversion, advantageously at least 0.2 times the NO _x conversion, extremely advantageously at least 0.3 times the NO _x conversion . _{This ensures that sufficient NO 2} is available both for the CH ₄ oxidation according to equation 1 and for the NO _x reduction according to equation 3. If the CH ₄ oxidation and SCR reduction catalyst are designed separately, exhaust gas upstream of the CH4 oxidation catalyst preferably has an NO ₂ content, based on a total content of nitrogen oxides, of at least 15%, preferably at least 30%, particularly preferably at least 50 %, on.

The combined or integrated CH ₄ oxidation and SCR reduction catalytic converter preferably has a beta zeolite, in particular a beta polymorph A-type (BEA) zeolite and / or a catalytically active compound _{for CH 4} oxidation and NO _{x reduction} Chabazite (CHA) zeolite and / or a pentasil type zeolite, in particular of the MFI type, such as ZSM-5 and / or a mordenite (MOR) zeolite, preferably elements of the respective zeolite with rare earth metals and / or iron and / or cobalt and / or nickel and / or copper and / or manganese are exchanged or substituted. With the second development, the exhaust gas aftertreatment system can be made even more compact. CH ₄ oxidation catalyst and the SCR reducing catalyst are provided ₄ -Oxidations- and SCR reducing catalyst according to the second modification, a combined or integrated CH. _{In order to enable highly efficient CH 4} oxidation and NOx reduction in the combined or integrated CH ₄ oxidation and SCR reduction catalyst, a defined catalytically active compound is first used in the catalyst, namely a beta zeolite, in particular a BEA Zeolite and / or a CHA zeolite and / or a pentasil type zeolite, in particular of the MFI type, such as ZSM-5, and / or a mordenite (MOR) zeolite. Furthermore, the NO ₂ proportion in the exhaust gas, based on the total proportion of nitrogen oxides, is set to at least 55%, preferably at least 60%, particularly preferably at least 70%, upstream of the combined or integrated CH ₄ oxidation and SCR reduction catalytic converter.

The internal combustion engine according to the invention is defined in claim 11.

• 1 eine stark schematisierte Ansicht einer ersten erfindungsgemäßen Brennkraftmaschine zur Verdeutlichung des erfindungsgemäßen Verfahrens zur Abgasnachbehandlung,
• 2 eine stark schematisierte Ansicht einer zweiten erfindungsgemäßen Brennkraftmaschine zur Verdeutlichung des erfindungsgemäßen Verfahrens zur Abgasnachbehandlung.

Preferred developments of the invention emerge from the subclaims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being restricted thereto. It shows:

• 1 a highly schematic view of a first internal combustion engine according to the invention to illustrate the method according to the invention for exhaust gas aftertreatment,
• 2 a highly schematic view of a second internal combustion engine according to the invention to illustrate the method according to the invention for exhaust gas aftertreatment.

The invention relates to an internal combustion engine in which a gaseous fuel is burned. The invention also relates to a method for aftertreatment of the exhaust gas from the internal combustion engine that burns the gaseous fuel.

1 shows a highly schematic diagram of an internal combustion engine according to the invention 1 . The internal combustion engine 1 has at least one cylinder block 2 with cylinders 3 . In the cylinders 3 the internal combustion engine 1 a gaseous fuel is burned, for example natural gas. In the internal combustion engine 1 it is either a gas engine or a dual fuel engine that can be operated in a gas fuel operating mode.

1 visualized with a feed 4th that the cylinders 3 the internal combustion engine is supplied with gaseous fuel, in particular a mixture of charge air and gas. A discharge 5 visualizes that exhaust gas from the cylinders is produced during combustion 3 discharged and via an exhaust aftertreatment system 6th the internal combustion engine 1 to be led.

The exhaust aftertreatment system 6th comprises a CH ₄ oxidation catalyst 7. The exhaust gas aftertreatment system 6th further comprises an SCR reduction catalyst 8th .

In the embodiment of 1 are the CH ₄ oxidation catalyst 7 and the SCR reduction catalyst 8th designed as separate or separate catalysts. The SCR reduction catalytic converter 8th is in the embodiment of 1 arranged downstream of the CH ₄ oxidation catalyst 7. Exhaust gas that _{leaves the CH 4} oxidation catalytic converter 7 is used to reduce the nitrogen oxide content in the exhaust gas via the SCR reduction catalytic converter 8th guided.

_{In this case, upstream of the CH 4} oxidation catalytic converter 7, seen in the flow direction of the exhaust gas, there is an introduction device 9 arranged for introducing NH ₃ or NH ₃ precursor substance into the exhaust gas in order to eliminate nitrogen oxides in the exhaust gas in the area of the SCR reduction catalytic converter 8th effectively reduce or reduce.

The fact that the feeding device 9 the NH ₃ or the NH ₃ precursor substance already introduces _{into the exhaust gas upstream of the CH 4} oxidation catalyst 7, there is no mixed section between the CH ₄ oxidation catalyst 7 and the SCR reduction catalyst 8th required. The same can then be arranged with the smallest possible spacing, preferably directly one behind the other, and particularly advantageously in a common housing 11 to be ordered.

In the embodiment of 1 contains the CH ₄ oxidation catalyst 7 for CH ₄ oxidation as a catalytically active compound at least one pyrochlore and / or at least one zeolite.

• Sm₂Zr₂O₇
• Sm₂Mo₂O₇
• La₂Ti₂O₇
• La₂CO_xSn_2-xO_7-δ
• La₂Co_xZr_2-xO_7-δ
• Mn₂Co_xZr_2-xO_7-δ
• Pr₂Ru₂O₇
• ZrTiGd₂O₇
• Pr₂Co₂O₇
• Pr₂Co_xZr_2-xO_7-δ

wobei 0≤δ≤2 und 0≤x≤1Then, if in the embodiment of the 1 the CH ₄ oxidation catalyst 7 for CH ₄ oxidation has at least one pyrochlore, the at least one pyrochlore can be selected from the following group:

• Sm ₂ Zr ₂ O ₇
• Sm ₂ Mo ₂ O ₇
• La ₂ Ti ₂ O ₇
• La ₂ CO _x Sn _2-x O _7-δ
• La ₂ Co _x Zr _2-x O _7-δ
• Mn ₂ Co _x Zr _2-x O _7-δ
• Pr ₂ Ru ₂ O ₇
• ZrTiGd ₂ O ₇
• Pr ₂ Co ₂ O ₇
• Pr ₂ Co _x Zr _2-x O _7-δ

where 0≤δ≤2 and 0≤x≤1

The CH ₄ oxidation catalyst 7 can comprise one or more or all of the above pyrochlores.

• MOR Zeolithe
• FER Zeolithe
• PER Zeolithe
• NFI Zeolithe
• LTL Zeolithe
• LAU Zeolithe
• CHI Zeolithe
• Beta- Zeolithe, insbesondere BEA Zeolithe
• CHA Zeolithe
• FAU Zeolithe
• LSX Zeolithe

Then, if in the embodiment of the 1 the CH ₄ oxidation catalyst 7 for CH ₄ oxidation has at least one zeolite, the at least one zeolite can be selected from the following group:

• MOR zeolites
• FER zeolites
• PER zeolites
• NFI zeolites
• LTL zeolites
• LAU zeolites
• CHI zeolites
• Beta zeolites, especially BEA zeolites
• CHA zeolites
• FAU zeolites
• LSX zeolites

The CH ₄ oxidation catalyst 7 can comprise one or more or all of the above zeolites.

If the CH ₄ oxidation catalyst 7 for CH ₄ oxidation and accordingly has a pyrochlore and / or at least one zeolite as the catalytically active compound, elements of pyrochloride and / or zeolite are preferably with rare earth metals and / or with iron and / or substituted with cobalt and / or with copper and / or with manganese.

Furthermore, the pyrochlore and / or the zeolite can be enriched with Rh, Ru, Ir, Os, Bi, Cn, Ed in that these elements are used in the pyrochlore and / or in the zeolite.

• CoO-Yb₂O₃
• NiO
• LiNiLaO
• LiCoLaO
• LiFeLaO
• NaNiLaO
• KNiLaO
• LiNiCeO
• LiNiYO
• LiNiSmOLaNiO
• Cu-Co-O
• Cu-Co-O
• La₂O₃
• SrO
• HfO₂
• YO₃
• ZrO₂
• MnO
• CuO
• TiO₂
• Fe₂O₃
• MoO₃

The CH ₄ oxidation catalyst 7 for CH ₄ oxidation can also contain at least one of the following compounds:

• CoO-Yb ₂ O ₃
• NOK
• LiNiLaO
• LiCoLaO
• LiFeLaO
• NaNiLaO
• KNiLaO
• LiNiCeO
• LiNiYO
• LiNiSmOLaNiO
• Cu-Co-O
• Cu-Co-O
• La ₂ O ₃
• SrO
• HfO ₂
• YO ₃
• ZrO ₂
• MnO
• CuO
• TiO ₂
• Fe ₂ O ₃
• MoO ₃

A proportion of platinum and palladium in the _{catalytically active active components used for the decomposition of CH 4} is in each case less than 1%, preferably less than 0.5%, extremely preferably less than 500 ppm.

According to an advantageous development, the proportion of the sum of platinum and palladium in the _{active components used for the CH 4} decomposition is less than 1%, advantageously less than 0.5%, extremely advantageously less than 1000 ppm.

_{The CH 4} oxidation catalyst is particularly preferably free from platinum and palladium.

_{Al 2} O ₃ , TiO ₂ , SiO ₂ and WO ₃ , individually or in combination, are preferably used as supports for the abovementioned catalytically active components.

In 1 If the exhaust gas to be routed via the CH _{4 oxidation catalyst 7 has an NO 2} proportion, based on the total proportion of nitrogen oxides in the exhaust gas, of at least 15%, preferably of at least 30%, particularly preferably of at least 50%. In 1 includes the exhaust aftertreatment system 6th upstream of the CH ₄ oxidation catalyst 7, an NO oxidation catalyst 10 to which the cylinder 3 leaving exhaust gas first via an NO oxidation catalyst 10 and with the help of the NO oxidation catalyst 10 to adjust the proportion of NO ₂ in the exhaust gas, based on the total proportion of nitrogen oxides in the exhaust gas, to at least 15%, preferably to at least 30%, particularly preferably to at least 50%. As an alternative or in addition to the NO oxidation catalytic converter 10 the NO ₂ content in the exhaust gas can also be determined via a combustion parameter of the internal combustion engine that burns the gaseous fuel 1 increase.

It is also possible that when, as in the exemplary embodiment of the 1 shown, the CH ₄ oxidation catalyst 7 and the SCR reduction catalyst 8th are designed as separate or separate catalysts, deviating from 1 the CH ₄ oxidation catalyst 7 downstream of the SCR reduction catalyst 8th to arrange. In this case, the exhaust gas of the internal combustion engine 1 first via the SCR reduction catalytic converter 8th and then passed over a separate CH ₄ oxidation catalytic converter 7, in which case that over the SCR reduction catalytic converter 8th Exhaust gas to be conducted has an NO ₂ proportion, based on a total proportion of nitrogen oxides, of at least 55%, preferably of at least 60%, particularly preferably of at least 70%. In addition, it has proven to be advantageous in this case if the NO ₂ content is at least 0.55 times the NO _x conversion, advantageously at least 0.65 times the NO _x conversion, extremely advantageously at least 0.75 times the NO _x - Conversion is, as this means that there is still sufficient NO _{2 available on the CH 4} oxidation catalyst downstream of the SCR catalyst for the oxidation of methane. With regard to the other details, refer to the statements above 1 to get expelled.

While in the embodiment of 1 the CH ₄ oxidation catalyst 7 and the SCR reduction catalyst 8th are designed as separate or separate catalysts, shows 2 a particularly advantageous embodiment of the invention, in which the CH ₄ oxidation catalyst 7 and the SCR reduction catalyst 8th of a combined or integrated CH ₄ oxidation and SCR reduction catalyst 12th are provided. This allows the exhaust gas aftertreatment system 6th can be made even more compact with minimal installation space.

In the embodiment of 2 it is provided that the proportion of NO ₂ in the exhaust gas is based on the total proportion of nitrogen oxides in the exhaust gas upstream of the combined CH ₄ oxidation and SCR reduction catalytic converter 12th is adjusted to at least 25%, preferably to at least 35%, particularly preferably to at least 55%. As in 2 shown, again via a NO Oxidation catalyst 10 take place, alternatively or additionally also by setting a combustion parameter of the internal combustion engine that burns the gaseous fuel. In addition, it has proven to be advantageous if the NO ₂ proportion is at least 0.1 times the NOx conversion, advantageously at least 0.2 times the NO _x conversion, extremely advantageously at least 0.3 times the NO _x conversion.

The above proportion of NO ₂ in the exhaust gas can prevent the SCR reduction reaction from _{consuming all of the NO 2} and no longer providing sufficient NO ₂ for the CH ₄ oxidation. With the above NO ₂ content in the exhaust gas, an effective CH ₄ oxidation and NOx reduction can therefore be ensured at the same time.

Such a combined or integrated CH ₄ oxidation and SCR reduction catalyst 12th has to _CH4 oxidation and NOx reduction as a catalytically active compound is a beta zeolite, in particular a beta polymorph A type (BEA) zeolite and / or a chabazite (CHA) of zeolite and / or a pentasil zeolite (MFI / ZSM-5) and / or a Mordernite (MOR) zeolite and / or a Ferrierite (FER) zeolite. These zeolites are suitable for both CH ₄ oxidation and, at the same time, for NOx reduction.

A particularly preferred CH ₄ oxidation and SCR reduction in the combined CH ₄ oxidation and SCR reduction catalyst 12th is possible if elements of the respective beta zeolite, in particular the BEA zeolite, and / or CHA zeolite and / or MFI zeolite and / or MOR zeolite and / or FER zeolite with rare earth metals and / or Iron and / or cobalt and / or copper and / or manganese are exchanged or substituted.

This combined catalyst is also characterized in that, at temperatures below 450 ° C., the nitrogen selectivity of the SCR reaction according to equations 2 and 3 is at least 70%, preferably at least 80%, extremely preferably at least 85%. This means that the oxidation of ammonia, which does not take place according to the above equations but rather via oxygen, is negligible. Ie the amount of oxidized ammonia according to the following equations is in total less than 30%, preferably less than 20%, extremely preferably less than 15% based on the amount of ammonia fed in upstream of the combination catalyst: 4NH3 + 3O ₂ → 2N ₂ + 6H ₂ O (Equation 4) 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O (Equation 5) 2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O (Equation 6)

• V₂O₅
• V₂O₄
• CoO-Yb₂O₃
• NiO
• LiNiLaO
• LiCoLaO
• LiFeLaO
• NaNiLaO
• KNiLaO
• LiNiCeO
• LiNiYO
• LiNiSmOLaNiO
• Cu-Co-O
• Cu-Co-O
• La₂O₃
• SrO
• HfO₂
• YO₃
• ZrO₂
• MnO
• CuO
• TiO₂
• Fe₂O₃
• MoO₃

The combined catalyst 12th for CH ₄ oxidation and NO _x reduction can also contain at least one of the following compounds:

• V ₂ O ₅
• V ₂ O ₄
• CoO-Yb ₂ O ₃
• NOK
• LiNiLaO
• LiCoLaO
• LiFeLaO
• NaNiLaO
• KNiLaO
• LiNiCeO
• LiNiYO
• LiNiSmOLaNiO
• Cu-Co-O
• Cu-Co-O
• La ₂ O ₃
• SrO
• HfO ₂
• YO ₃
• ZrO ₂
• MnO
• CuO
• TiO ₂
• Fe ₂ O ₃
• MoO ₃

In the internal combustion engine 1 it can be both a gas engine and a dual-fuel engine that can be operated in a gas-fuel operating mode.

Then when the embodiment of the 2 is used in a dual-fuel engine, in which both gaseous fuel and liquid fuel are burned in a gas fuel operating mode, can be provided with an increasing proportion of the gaseous fuel and accordingly with an increasing reduction in the proportion of burned liquid fuel that is introduced into the exhaust gas to reduce amount of NH ₃ or NH ₃ amount of -Vorläufersubstanz. _{As a result, the NO x} converted on the catalytic converter with SCR activity - and thus the converted NO ₂ - amount decreases. As a result, there is then a combined CH ₄ oxidation and SCR reduction catalyst 12th a sufficient amount of NO ₂ is available to effectively oxidize _{the CH 4.} If, on the other hand, a higher proportion of liquid fuel with a decreasing proportion of gaseous fuel is burned in the dual-fuel engine, fewer CH ₄ emissions are produced and the amount of NO ₂ required for the CH 4 oxidation is reduced, so that more NH _{4 is produced 3} or more of the NH ₃ precursor substance for NOx reduction is introduced into the exhaust gas, so that the amount of _{NO x converted increases.}

List of reference symbols

1

Internal combustion engine

2

Cylinder block

3

cylinder

4th

Feed

5

Discharge

6th

Exhaust aftertreatment system

7th

CH ₄ oxidation catalyst

8th

SCR catalytic converter

9

Feeding device

10

NO oxidation catalyst

11

casing

12th

CH ₄ oxidation and SCR reduction catalyst

QUOTES INCLUDED IN THE DESCRIPTION

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Patent literature cited

• DE 102015001495 A1 [0005, 0006, 0007]

Claims (14)

Method for the aftertreatment of the exhaust gas of an internal combustion engine (1) which burns a gaseous fuel, namely a gas engine or a dual-fuel engine which can be operated in a gas fuel operating mode, the exhaust gas being _{supplied via a CH 4} oxidation catalyst (7) and via an SCR _{-Reduction catalyst (8) is performed, with NH 3} or an NH ₃ precursor substance being introduced into the exhaust gas upstream of the CH ₄ oxidation catalyst (7) as the reducing agent for the SCR reduction catalyst (8). Procedure according to Claim 1 , characterized in that the exhaust gas from the internal combustion engine (1) is first passed over the CH ₄ oxidation catalytic converter (7) and then over a separate SCR reduction catalytic converter (8). Procedure according to Claim 2 , characterized in that the exhaust gas to be routed via the CH ₄ oxidation catalyst (7) has an NO ₂ proportion, based on a total proportion of nitrogen oxides, of at least 15%, preferably of at least 30%, particularly preferably of at least 50% . Procedure according to Claim 1 , characterized in that the exhaust gas from the internal combustion engine (1) is first passed over the SCR reduction _{catalytic converter (8) and then over a separate CH 4} oxidation catalytic converter (7). Procedure according to Claim 4 , characterized in that the exhaust gas to be routed via the SCR reduction catalytic converter (8) has an NO ₂ proportion, based on a total proportion of nitrogen oxides, of at least 55%, preferably of at least 60%, particularly preferably of at least 70%. Method according to one of the Claims 1 to 5 , characterized in that the CH ₄ oxidation catalyst (7) for CH ₄ oxidation and accordingly has at least one pyrochlore and / or at least one zeolite as the active compound, preferably elements of pyrochloride and / or zeolite with rare earth metals and / or iron and / or cobalt and / or copper and / or manganese are exchanged or substituted. Procedure according to Claim 1 , characterized in that the exhaust gas of the internal combustion engine (1) is passed over a combined or integrated CH ₄ oxidation and SCR reduction catalyst (12), the NH ₃ or the NH ₃ precursor substance upstream of the combined or oxidation and SCR -Reduction catalyst (12) is introduced into the exhaust gas. Procedure according to Claim 7 , characterized in that the combined or integrated CH ₄ oxidation and SCR reduction catalyst (12) for CH ₄ oxidation and NO _x reduction as a catalytically active compound, at least one zeolite, in particular a beta zeolite, in particular a beta polymorph A -Type (BEA) zeolite, and / or a chabazite (CHA) zeolite and / or a zeolite of the pentasil type (MFI) and / or a mordenite (MOR) zeolite and / or a ferrierite (FER) zeolite, with preferably Elements of the respective zeolite are exchanged or substituted with rare earth metals and / or iron and / or cobalt and / or copper and / or manganese. Procedure according to Claim 7 or 8th , characterized in that the exhaust gas to be conducted via the combined or integrated CH ₄ oxidation and SCR reduction catalytic converter (12) has an NO ₂ proportion, based on a total proportion of nitrogen oxides, of at least 25%, preferably of at least 35% , particularly preferably of at least 55%. Procedure according to Claim 3 , 5 or 9 , characterized in that the NO ₂ proportion in the exhaust gas is set via at least one combustion parameter of the internal combustion engine (1) which burns the gaseous fuel, and / or the NO ₂ proportion in the exhaust gas is set via an NO oxidation catalytic converter (10). Internal combustion engine (1), namely a gas engine or dual-fuel engine, with cylinders (3) in which a gaseous fuel is combustible, with an exhaust gas aftertreatment system (6), the exhaust gas aftertreatment system (6) having a CH ₄ oxidation catalyst (7) and an SCR reduction catalytic converter (8), the exhaust gas aftertreatment system (6) _{having an introduction device (9) arranged upstream of the CH 4} oxidation catalytic converter (7) for introducing NH ₃ or an NH ₃ precursor substance into the exhaust gas as a reducing agent for the SCR Has reduction catalyst (8). Internal combustion engine after Claim 11 , characterized in that the CH ₄ oxidation catalyst (7) and the and the SCR reduction catalyst (8) as separate or separate catalysts are formed, wherein the CH ₄ oxidation catalyst (7) is arranged upstream of the SCR reduction catalyst (8). Internal combustion engine after Claim 11 , characterized in that the CH ₄ oxidation catalyst (7) and the and the SCR reduction catalyst (8) are designed as separate or separate catalysts, the CH ₄ oxidation catalyst (7) being arranged downstream of the SCR reduction catalyst (8) . Internal combustion engine after Claim 11 , characterized in that the CH ₄ oxidation catalyst (7) and the SCR reduction catalyst (8) are provided by a combined or integrated CH ₄ oxidation and SCR reduction catalyst (12).

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