Catalytic Converter Configuration and Method for Desulfurizing a NOx Storage Catalytic Converter

Abstract

A catalytic converter configuration for an internal combustion engine that is capable of running lean has an exhaust gas duct and a NO.sub.x storage catalytic converter arranged in the exhaust gas duct. A novel method allows desulfurizing the NO.sub.x storage catalytic converter. An H.sub.2S storage catalytic converter is provided. This catalytic converter is capable of storing hydrogen sulfide under a rich or stoichiometric exhaust gas atmosphere with lambda.ltoreq.1 and oxidizing hydrogen sulfide under a lean exhaust gas atmosphere with lambda>1.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority, under 35 U.S.C. .sctn.119, of German patent application DE 10 2006 038 367.2, filed Aug. 16, 2006; the prior application is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The invention relates to a catalytic converter configuration for internal combustion engines capable of running lean and having a NO.sub.x storage catalytic converter arranged in their exhaust gas duct. The invention also relates to a method for desulfurizing the NO.sub.x storage catalytic converter.

[0003] In internal combustion engines which are operated with a lean fuel-air mixture, traditional three-way catalytic converters are not sufficient for quantitative conversion of all exhaust gas constituents, in particular nitrogen oxides NO.sub.x. Therefore, the arrangement of so-called NO.sub.x storage catalytic converters in the exhaust gas ducts of such internal combustion engines is known. NO.sub.x storage catalytic converters have a NO.sub.x storage component which stores NO.sub.x under a lean exhaust gas atmosphere. NO.sub.x regeneration is performed through short rich intervals during which the stored NO.sub.x is desorbed and converted to N.sub.2 and O.sub.2 by means of a catalytic component of the NO.sub.x storage catalytic converter. The use of NO.sub.x storage catalytic converters is known in both diesel engines and lean mix gasoline engines.

[0004] Due to the sulfur that is present in the fuel, the NO.sub.x storage catalytic converter loses activity over its surface life. This is referred to as sulfur poisoning. The sulfur is deposited in the form of sulfate on the storage components of the catalytic converter, thereby blocking the NO.sub.x storage sites of the storage catalytic converter so they are no longer available for storing NO.sub.x. If a lower limit of NO.sub.x storage capacity of the NO.sub.x storage catalytic converter is reached, it must be desulfurized (desulfated). This is performed at high exhaust gas temperatures of at least 500.degree. C. by exposing the storage catalytic converter to a rich exhaust gas atmosphere (lambda<1). At these temperatures, the stored sulfur is desorbed and reduced to SO.sub.2 by the reducing exhaust gas atmosphere while also being reduced to hydrogen sulfide H.sub.2S. The richer the exhaust gas conditions during desulfurization, the faster the desorption and reduction of sulfur take place, which has positive effects on thermal aging of the storage catalytic converter, but is associated with an increase in the unwanted formation of H.sub.2S.

[0005] It is known that to perform desulfurization, the engine is operated alternately in rich operation with lambda<1 and in lean operation with lambda>1 for short intervals of time, i.e., in so-called wobble operation. This promotes the heating of the catalytic converter to the required desulfurization temperature and maintaining same. Furthermore, due to the alternating exposure of the storage catalytic converter to rich and lean exhaust gas, production of H.sub.2S is decreased because in the lean intervals oxygen is incorporated into the catalytic converter, thereby ensuring oxidation of H.sub.2S, which is formed as an intermediate, to SO.sub.2. However, it has been found that complete desulfurization of a storage catalytic converter in wobble operation is also associated with a certain production of H.sub.2S, the concentration of which may result in exceeding limit values.

SUMMARY OF THE INVENTION

[0006] It is accordingly an object of the invention to provide a catalytic converter configuration and a method for desulfurizing a NO.sub.x storage catalyst which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allows desulfurizing the NO.sub.x storage catalyst in such a way that it protects the catalytic converter and in which production of H.sub.2S is minimized. It is a concomitant object to provide for a catalytic converter configuration that is suitable for implementing the novel method.

[0007] With the foregoing and other objects in view there is provided, in accordance with the invention, a catalytic converter configuration for an internal combustion engine that is capable of running lean, comprising:

[0008] an exhaust gas duct connected with the internal combustion engine;

[0009] a NO.sub.x storage catalytic converter disposed in said exhaust gas duct; and

[0010] an H.sub.2S storage catalytic converter configured to store hydrogen sulfide under a rich or stoichiometric exhaust gas atmosphere with lambda.ltoreq.1 and to release the hydrogen sulfide under a lean exhaust gas atmosphere with lambda>1.

[0011] In other words, the objects of the invention are achieved by a catalytic converter configuration that includes an H.sub.2S storage catalytic converter that is suitable for storing hydrogen sulfide H.sub.2S under rich or stoichiometric exhaust gas atmosphere, i.e., with an air/fuel ratio of lambda.ltoreq.1 and then releasing it in a lean exhaust gas atmosphere, with lambda>1, in particular essentially as sulfur dioxide SO.sub.2. Through the inventive arrangement of the H.sub.2S storage catalytic converter it is possible to desulfurize the NO.sub.x storage catalytic converter under constantly rich exhaust gas conditions and thus at relatively low temperatures, thereby delaying its thermal aging. At the same time unwanted H.sub.2S emissions are greatly reduced or even prevented entirely.

[0012] According to an advantageous embodiment of the invention, the H.sub.2S storage catalytic converter is connected downstream from the NO.sub.x storage catalytic converter in the direction of flow of the exhaust gas, the H2S storage catalytic converter being arranged directly adjacent to the NO.sub.x storage catalytic converter or at a distance therefrom. As an alternative the H.sub.2S storage catalytic converter may also be integrated into the NO.sub.x storage catalytic converter, i.e., there may be a mixed coating of H.sub.2S and NO.sub.x storage catalytic converter components on a common support for the catalytic converter. All these requirements ensure that the H.sub.2S released from the NO.sub.x storage catalytic converter is stored and converted in the H.sub.2S storage catalytic converter.

[0013] As the H.sub.2S storage component of the H.sub.2S storage catalytic converter, it preferably contains a metal component which is suitable for binding H.sub.2S as metal sulfide in particular under rich or stoichiometric exhaust gas atmosphere. The prerequisite for selecting the suitable metal component is its suitability for entering into a metal-sulfur compound in the rich exhaust gas and releasing the sulfur, preferably in the form of SO.sub.2, under lean conditions. Metals of subgroups I, II and/or VIII of the periodic system of elements are especially suitable for this purpose, preferably using silver (Ag), zinc (Zn), cadmium (Cd), iron (Fe), cobalt (Co) and/or nickel (Ni). The loading of the H.sub.2S storage catalytic converter with the metal component depends on the desired H.sub.2S storage capacity of the H.sub.2S storage catalytic converter, in particular after typical sulfur loading of the NO.sub.x storage catalytic converter to be removed at the time of its desulfurization. In typical cases, a specific metal loading of at least 0.2 g/l has proven advantageous, in particular at least 0.3 g/L, especially preferably at least 0.5 g/l.

[0014] Furthermore it is preferably also provided that the H.sub.2S storage catalytic converter may additionally have an oxidation catalytic component or a three-way catalytic component under a lean exhaust gas atmosphere, i.e., it catalyzes oxidation of carbon moNOxide CO and/or hydrocarbons HC and--in the case of a three-way catalytic effect--additionally supports reduction of nitrogen oxides NO.sub.x. To do so, the catalytic converter may additionally contain at least one noble metal, e.g., platinum (Pt), palladium (Pd) and/or rhodium (Rh).

[0015] Another advantageous embodiment according to the invention, the catalytic converter configuration also has an oxygen-storing component downstream from the NO.sub.x storage catalytic converter and/or the H.sub.2S storage catalytic converter, this oxygen-storing component being capable of storing oxygen in a lean exhaust gas atmosphere and releasing oxygen under a rich exhaust gas atmosphere, so that H.sub.2S desorbed from the NO.sub.x storage catalytic converter is oxidized to SO.sub.2. Such oxygen-storing components (OSC for oxygen storage component) are known in the state of the art and therefore will not be explained further here. In addition with the help of the oxygen stored in the OSC, the components CO and HC can also be converted and thus emissions in rich operation can be reduced.

[0016] The present invention also relates to a method for desulfurizing a NO.sub.x storage catalytic converter in which hydrogen sulfide coming from the NO.sub.x storage catalytic converter is stored in an H.sub.2S storage catalytic converter and is released again, preferably as SO.sub.2 under a lean exhaust gas atmosphere having a lambda>1 in particular above a certain catalytic converter temperature. The release temperature in the H.sub.2S storage catalytic converter may be induced by an upstream particle filter reaction, for example (by way of PF regeneration).

[0017] It is especially advantageous to alternately treat the NO.sub.x storage catalytic converter in so-called wobble operation during desulfurization, i.e., with rich intervals with lambda.ltoreq.1 and lean intervals with lambda>1. However, the desulfurization may also essentially be performed in continuous rich operation of the internal combustion engine using the catalytic converter configuration described above.

[0018] Other features which are considered as characteristic for the invention are set forth in the appended claims.

[0019] Although the invention is illustrated and described herein as embodied in catalytic converter configuration and method for desulfurizing a NO.sub.x storage catalytic converter, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

[0020] The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0021] FIG. 1 shows an internal combustion engine having a downstream catalytic converter configuration according to a first embodiment of the invention;

[0022] FIG. 2 shows an internal combustion engine having a downstream catalytic converter configuration according to a second embodiment of the invention;

[0023] FIG. 3 shows an internal combustion engine having a downstream catalytic converter configuration according to a third embodiment of the invention;

[0024] FIG. 4 shows curves of the lambda value as a function of time, measured upstream and downstream from the NO.sub.x storage catalytic converter as well as the SO.sub.2 and H.sub.2S concentrations after the NO.sub.x storage catalytic converter during desulfurization of the NO.sub.x storage catalytic converter in the catalytic converter configuration according to FIG. 1; and

[0025] FIG. 5 shows curves of the SO.sub.2 and H.sub.2S concentrations downstream from the NO.sub.x storage catalytic converter according to the present invention and the state of the art as a function of time.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is illustrated an internal combustion engine 10 which can be operated with a lean air-fuel mixture. This may be a diesel engine or a gasoline engine capable of running lean.

[0027] According to a first advantageous embodiment of the present invention, a catalytic converter configuration 12 is connected downstream from the internal combustion engine 10. Exhaust gas emanating from the internal combustion engine 10 is directed into the catalytic converter configuration, where it is after-treated. The catalytic converter configuration 12 comprises an exhaust gas duct 14 in which various catalytic converters are arranged. According to the embodiment depicted here, an oxidation catalytic converter or a three-way catalytic converter that acts as a precatalytic converter 16 is arranged in a position near the internal combustion engine 10. Alternatively or in addition to the precatalytic converter 16 a particulate filter (not shown here) may also be arranged near the engine for storing soot (carbon black) particles and may optionally also be combined with the oxidative or three-way precatalytic converter 16 on a common support.

[0028] Downstream from the precatalytic converter 16 (and/or the particle filter provided as an alternative or in addition), a NO.sub.x storage catalytic converter 18 is provided in the exhaust gas duct 14. The NO.sub.x storage catalytic converter 18 has a NO.sub.x storage component which stores NO.sub.x under a lean exhaust gas atmosphere and releases it again in the intermediate regeneration intervals during which the internal combustion engine 10 is operated with a stoichiometric or rich air-fuel mixture. An oxidation component or three-way component integrated into the NO.sub.x storage catalytic converter 18 catalyzes the reaction of the desorbed nitrogen oxides N.sub.2 and oxygen O.sub.2 during the NO.sub.x regeneration.

[0029] In addition to NO.sub.x storage, incorporation of sulfur present in the fuel also takes place in the form of sulfate in the NO.sub.x storage catalytic converter 18 in an unwanted manner. Since the sulfur is not removed from the NO.sub.x storage catalytic converter 18 during the usual NO.sub.x regeneration thereof, it therefore accumulates in the storage catalytic converter 18 and leads to increasing blockage of the NO.sub.x storage sites. To ensure an adequate NO.sub.x storage activity, desulfurization is performed at greater intervals. To do so, the NO.sub.x storage catalytic converter 18 is heated to a desulfurization temperature of 550.degree. C. or more, for example, through engine-related measures, and is at least temporarily exposed to a rich or stoichiometric exhaust gas atmosphere having a lambda<1. Under these conditions, sulfur is desorbed and released mainly in the form of sulfur dioxide SO.sub.2. However, a portion of the sulfur is released in the form of hydrogen sulfide H.sub.2S during the desulfurization, which is also unwanted because of the toxicity of H.sub.2S and its odor problem. The formation of H.sub.2S is even more intense, the richer the air-fuel mixture and the longer the NO.sub.x storage catalytic converter 18 is exposed to the rich exhaust gas. On the other hand, complete desulfurization of the NO.sub.x storage catalytic converter 18 cannot be achieved with an air-fuel mixture that is only slightly rich and/or desulfurization must be performed at higher catalytic converter temperatures, which is associated with a thermal burden on the NO.sub.x storage catalytic converter 18 and an increased fuel consumption.

[0030] To avoid this problem, the catalytic converter configuration 12 according to this invention has an H.sub.2S storage catalytic converter 20 which is arranged downstream from the NO.sub.x storage catalytic converter 18 and directly adjacent thereto in the example shown in FIG. 1. The H.sub.2S storage catalytic converter 20 is designed to store H.sub.2S in the form of a metal sulfide in particular under rich exhaust gas conditions and to release and oxidize it to SO.sub.2 under lean exhaust gas conditions. For example, a coating comprising a transition metal, e.g., nickel that binds H.sub.2S as nickel sulfide is suitable for this. The H.sub.2S storage catalytic converter 20 advantageously also has a three-way catalytic component that is responsible for the reaction of HC, CO and NO.sub.x during lean operation of the internal combustion engine 10, so that the H.sub.2S storage catalytic converter 20 supports the precatalytic converter 16 or may even replace it. In comparison with conventional three-way catalytic converters, the coating of the H.sub.2S storage catalytic converter 20 has a much greater loading with the transition metal. The transition metal loading of the H.sub.2S storage catalytic converter 20 depends on the sulfur load typically preventing in desulfurization of the NO.sub.x storage catalytic converter 18, amounting to at least 0.2 g per liter catalytic converter volume, for example. The arrangement of the H.sub.2S storage catalytic converter 20 allows desulfurization of the NO.sub.x storage catalytic converter 18 to be performed at relatively low temperatures and low lambda values without having to accept undesirable H.sub.2S emissions. Due to the low desulfurization temperatures, a thermal burden on the NO.sub.x storage catalytic converter 18 and thus a shortening of its lifetime are prevented. According to the example illustrated in FIG. 1, the NO.sub.x and the H.sub.2S storage catalytic converters 18, 20 may be designed as spatially separate zones on one and the same catalytic converter support or on a separate catalytic converter support directly adjacent to one another.

[0031] The exhaust gas duct also contains various gas sensors. Upstream from the precatalytic converter 16 (and/or the particulate filter) there is an oxygen-sensitive gas sensor 22, in particular a lambda probe which regulates the lambda regulation [sic; enables lambda regulation] of the air-fuel mixture of the internal combustion engine 10 in a known way. Another oxygen-sensitive gas sensor 24 is arranged downstream from the H.sub.2S storage catalytic converter 20. This may also be a lambda probe or a NO.sub.x sensor, which supplies an oxygen-dependent signal. Additional gas sensors and/or temperature sensors may also be additionally installed in the exhaust gas duct 14.

[0032] The internal combustion engine 10 is supplied with air through an air intake duct 26 in which there is an adjustable throttle valve 28. An electronic engine control unit 30 which is provided for controlling the internal combustion engine 10 receives the signals of the gas sensors 22 and 24, any other gas and/or temperature sensors that might be present as well as various operating parameters of the internal combustion engine 10, e.g., rotational speed, the driver's intended torque, etc. Depending on this data, the engine control unit 30 executes the control using stored characteristic lines and/or engine characteristics maps, to which end the control unit influences parameters, e.g., the quantity the fuel, the injection point in time, the firing angle (in gasoline engines), the exhaust gas recirculation EGR rate, air mass, etc. The engine control unit 30 in particular also contains a program algorithm for operating the exhaust gas system 12, in particular for performing the desulfurization of the NO.sub.x storage catalytic converter 18.

[0033] FIGS. 2 and 3 show other embodiments of the inventive catalytic converter configuration 12, whereby corresponding elements are labeled with the same reference numerals as those shown in FIG. 1. For the sake of simplicity, the signal lines and the engine control unit are not shown in FIGS. 2 and 3.

[0034] The system shown in FIG. 2 differs from that in FIG. 1 in that the NO.sub.x storage catalytic converter 18 and the H.sub.2S storage catalytic converter 20 are not installed adjacent to one another but instead are installed with a distance between them in the exhaust gas duct 14. In this constellation, the oxygen-sensitive gas sensor 24 is preferably arranged between the storage catalytic converters 18 and 20.

[0035] In the embodiment shown in FIG. 3, the NO.sub.x storage catalytic converter 18 and the H.sub.2S storage catalytic converter 20 are present as a mixed coating on the same catalytic converter support, i.e., no local separation of the two functions is provided here.

[0036] Performance of a method for desulfurizing a NO.sub.x storage catalytic converter in a system according to FIG. 1 but without the H.sub.2S storage catalytic converter 20 is illustrated in a typical embodiment on the basis of the curve of various exhaust gas parameters as a function of time in FIG. 4. The NO.sub.x storage catalytic converter used here has a total noble metal load of Pt, Pd and Rh amounting to 110 g/ft.sup.3 as well as barium (Ba) and cerium (Ce) as NO.sub.x storage components. In FIG. 4, curve 100 shows the lambda value measured with the lambda probe 22 upstream from the NO.sub.x storage catalytic converter 18 during its desulfurization, while curve 102 shows the lambda value measured with the lambda probe 24 downstream from the NO.sub.x storage catalytic converter 18. Curves 104 and 106 show the emissions of sulfur dioxide SO.sub.2 and/or hydrogen sulfide H.sub.2S measured at the exhaust outlet downstream from the NO.sub.x storage catalytic converter. Except for the H.sub.2S curve (curve 106), the execution of the inventive method for desulfurizing the NO.sub.x storage catalytic converter 18, i.e., using an H.sub.2S storage catalytic converter 20, corresponds in principle to that illustrated in FIG. 4.

[0037] First, starting from a leaner exhaust gas atmosphere with lambda.apprxeq.1.01 a rich exhaust gas atmosphere with lambda.apprxeq.0.98 is adjusted for heated the NO.sub.x storage catalytic converter 18 and for initiating its desulfurization. As soon as the rich exhaust gas reaches the NO.sub.x storage catalytic converter 18, it leads to an intense release of SO.sub.2 (curve 104, point in time 176000). However, release of SO.sub.2 drops again very rapidly in favor of an increase in the H.sub.2S emissions (curve 106). Starting approximately at the point in time 192000, so-called wobble operation is begun, in which the internal combustion 10 is operated alternately with a lean air-fuel mixture with lambda.apprxeq.1.01 and a rich air-fuel mixture with lambda.apprxeq.0.98. The lambda curve 102 measured downstream from the NO.sub.x storage catalytic converter 18 follows this change with a certain delay and with reduced amplitudes, which is caused first by the exhaust gas running time and secondly by the consumption of oxygen in the exhaust gas to reduce the sulfur. Switching between lean and rich intervals is regulated by the lambda probe 24 downstream from the NO.sub.x storage catalytic converter 18. The switch from lean to rich is made as soon as the probe detects a lean exhaust gas. Conversely, the switch from rich to lean is made as soon as the lambda probe 24 records the breakthrough of rich exhaust gas. In each rich interval, an increase in SO.sub.2 emission 104 downstream from the NO.sub.x storage catalytic converter 18 can be observed, declining toward the end of the rich interval--with increasing consumption of the oxygen incorporated in the lean intervals--in favor of the H.sub.2S emission 106.

[0038] FIG. 5 shows comparatively the H.sub.2S emissions according to the state of the art (see FIG. 4) and according to the present invention for the entire duration of desulfurization. Curve 108 shows the measured final H.sub.2S emission at the exhaust gas outlet of an exhaust gas system according to the state of the art without a downstream H.sub.2S storage catalytic converter. Curve 110 however shows the corresponding curve with an exhaust gas arrangement having an H.sub.2S storage catalytic converter 20 according to FIG. 1. In both cases a NO.sub.x storage catalytic converter having a total noble metal load of 110 g/ft.sup.3 Pt, Pd and Rh plus barium (Ba) and cerium (Ce) as NO.sub.x storage components was used. In the inventive curve as represented by curve 110, an H.sub.2S storage catalytic converter 20 having a nickel load of >0.5 g/L was additionally used. It can be seen clearly here that the total H.sub.2S emissions according to the present invention are reduced to a fraction in comparison with the state of the art. To achieve a regeneration of the H.sub.2S storage catalytic converter 20 following the desulfurization and thus to restore the H.sub.2S storage function at the start of the next desulfurization process, the catalytic converter is exposed to a lean exhaust gas atmosphere at an elevated exhaust gas temperature. In doing so, the sulfur is oxidized to SO.sub.2 and removed from the surface of the catalytic converter 20. For regeneration of the H.sub.2S storage catalytic converter, standard operating situations of the internal combustion engine 10 may be utilized. For example, regeneration may be performed during the heating phase for desulfurization of the NO.sub.x storage catalytic converter 18 or--in a diesel vehicle--during a heating phase of particulate filter regeneration. In addition, it may also be performed in driving situations of moderate load, in which there is an increase in temperature of the exhaust gas in a lean exhaust gas atmosphere. With all the aforementioned modes of operation of the internal combustion engine 10, formation of SO.sub.2 is facilitated by the high exhaust gas temperature and the oxygen excess of the exhaust gas.

Claims

1. A catalytic converter configuration for an internal combustion engine that is capable of running lean, comprising: an exhaust gas duct connected with the internal combustion engine; a NO.sub.x storage catalytic converter disposed in said exhaust gas duct; and an H.sub.2S storage catalytic converter configured to store hydrogen sulfide under a rich or stoichiometric exhaust gas atmosphere with lambda.ltoreq.1 and to release the hydrogen sulfide under a lean exhaust gas atmosphere with lambda>1.

2. The catalytic converter configuration according to claim 1, wherein said H.sub.2S storage catalytic converter is disposed downstream and at a spacing distance from said NO.sub.x storage catalytic converter.

3. The catalytic converter configuration according to claim 1, wherein said H.sub.2S storage catalytic converter is disposed downstream and adjoining said NO.sub.x storage catalytic converter.

4. The catalytic converter configuration according to claim 1, wherein said H.sub.2S storage catalytic converter is integrated in said NO.sub.x storage catalytic converter.

5. The catalytic converter configuration according to claim 1, wherein said H.sub.2S storage catalytic converter contains at least one metal component suitable for binding H.sub.2S as a metal sulfide under a rich or stoichiometric exhaust gas atmosphere with lambda.ltoreq.1.

6. The catalytic converter configuration according to claim 5, wherein said metal component includes at least one metal of subgroups I, II and/or VIII of the table of elements.

7. The catalytic converter configuration according to claim 5, wherein said metal component includes at least one component selected from the group consisting of Ag, Zn, Cd, Fe, Co, and Ni.

8. The catalytic converter configuration according to claim 5, wherein a specific loading of said H.sub.2S catalytic converter with said at least one metal component amounts to at least 0.2 grams per liter.

9. The catalytic converter configuration according to claim 5, wherein a specific loading of said H.sub.2S catalytic converter with said at least one metal component amounts to at least 0.5 grams per liter.

10. The catalytic converter configuration according to claim 1, wherein said H.sub.2S storage catalytic converter additionally has an oxidation catalytic component or a three-way catalytic component.

11. The catalytic converter configuration according to claim 5, wherein said H.sub.2S storage catalytic converter contains at least one noble metal component.

12. The catalytic converter configuration according to claim 11, wherein said noble metal component is selected from the group consisting of platinum, palladium, and rhodium.

13. The catalytic converter configuration according to claim 1, which further comprises a component for storing oxygen disposed downstream of said NO.sub.x storage catalytic converter and/or of said H.sub.2S storage catalytic converter.

14. The catalytic converter configuration according to claim 1, which comprises an oxygen-sensitive gas sensor disposed downstream of said NO.sub.x storage catalytic converter and/or of said H.sub.2S storage catalytic converter.

15. The catalytic converter configuration according to claim 14, wherein said oxygen-sensitive gas sensor is a lambda probe or a NO.sub.x sensor.

16. A method of desulfurizing a NO.sub.x storage catalytic converter disposed in an exhaust gas duct of an internal combustion engine that is capable of running lean, which comprises: exposing the NO.sub.x storage catalytic converter at least temporarily to a rich or stoichiometric exhaust gas atmosphere with lambda.ltoreq.1 at a desulfurization temperature of the NO.sub.x storage catalytic converter; and storing hydrogen sulfide released from the NO.sub.x storage catalytic converter in an H.sub.2S storage catalytic converter; and releasing the hydrogen sulfide in a lean exhaust gas atmosphere with lambda>1.

17. The method according to claim 16, which comprises, during desulfurization, alternately exposing the NO.sub.x storage catalytic converter to rich intervals with a rich or stoichiometric exhaust gas atmosphere with lambda.ltoreq.1 and in lean intervals to a lean exhaust gas atmosphere with lambda>1.

18. The method according to claim 16, which comprises regenerating the H.sub.2S storage catalytic converter by an oxidation product of H.sub.2S.

19. The method according to claim 16, which comprises regenerating the H.sub.2S storage catalytic converter by regeneration of SO.sub.2 by exposure of the H2S storage catalytic converter to a lean exhaust gas atmosphere and a minimum temperature.