DE10252733A1 - Device for purifying vehicle exhaust gases used in diesel engines comprises a filter body having a region for sulfur oxides storage - Google Patents

Abstract

Device for purifying vehicle exhaust gases comprises a filter body having a first region (18) for SOx storage.

Description

The invention relates to a device for cleaning exhaust gases from a motor vehicle.

In the case of diesel motor vehicles in particular, the reduction of NO _x and particle emissions is a problem when the exhaust gas limit values are reached. For diesel vehicles, for example, a denitrification process based on the effect of a NO _x storage catalytic converter is being tested. In this, the nitrogen oxides are generally adsorbed and the adsorbed nitrogen oxides are periodically reductively desorbed from the storage within short fat phases and converted on the catalyst.

However, the problem with NO _x storage catalysts is their susceptibility to sulfur oxides. These are more strongly adsorbed on the storage component than nitrogen oxides and therefore block the access of the nitrogen oxides to the storage locations. For this reason, a sulfur-poisoned catalyst must be freed of sulfur after a certain period of time. Desulphurization can be achieved in whole or in part by such a desulfurization process. This takes place at temperatures from 400 to 800 ° C and an air ratio of λ <1 in a period of several seconds to several minutes.

It should be noted that high sulfur concentrations in the exhaust gas and high exhaust gas temperatures the growth of metal sulfate crystals promote from the active components (e.g. Ba, Sr). This increases the danger that the Catalyst no longer completely can be desulfurized. Therefore, it is necessary to have higher regeneration temperatures use. Both very high desulfurization temperatures as well an incomplete Desulfurization can but irreversible loss of activity of the catalyst.

Therefore, the prior art tries to to protect the catalyst from sulfur. A possibility is to eliminate sulfur components in the fuel. So far, however, residual amounts of sulfur remain present as 5 ppm in the fuel. It also currently starts at Fuel sulfur levels of less than 10 ppm contribute of the engine oil to Outweigh the sulfur content of the exhaust gas.

A known measure provides for so-called SO _x traps to be provided in the exhaust tract in order to protect the NO _x storage catalytic converter from sulfur. It has proven to be expedient to implement a spatial separation between the SO _x trap and the NO _x store, so that the SO _x -containing exhaust gas first comes into contact with the SO _x trap.

Furthermore, it is known to coat a layer containing a NO _x storage catalyst with a layer of SO _x storage material. It is also known to arrange a SO _x trap upstream of a NO _x storage device. In a construction of a two-line system based on this, each line contains a NO _x store and an upstream SO _x store. It is arranged upstream of the NO _x storage catalyst during the SO _x -Einspeicherung the SO _x storage. In the SO _x regeneration, a flap system is used to implement the reverse order.

NO _x reduction methods may no longer be sufficient for future exhaust gas regulations. The installation of post-engine NO _x and particle reduction devices may be necessary for these vehicles. Several models, for example catalytic converters or filters, have to be connected in series in the exhaust line, which is costly and space-intensive and can furthermore lead to high pressure losses in the exhaust line.

It has been shown that a module which combines several components, for example particles and NO _x reduction systems, has the advantage of saving costs and space. At the same time, high pressure losses in the exhaust system are counteracted.

Systems of this type are already known which contain a particle filter and a NO _x storage catalytic converter. With these it is advantageous that a NO _x storage desulfation and a particle filter regeneration can take place simultaneously.

From the publication DE 198 50 757 A1 a method and a device for desulfating a catalyst device are known. In the method presented, the heat released during the regeneration of a particle filter is used to regenerate the deactivated catalyst surface. The described device comprises a catalytic converter, a particle filter and a heat transfer device.

In contrast, in the device according to the invention for cleaning exhaust gases from a motor vehicle, a particle filter body is provided which has or carries an area which is designed for SO _x storage.

SO _x traps or SO _x stores preferably contain moderately to strongly basic element oxides, for example their hydroxides, carbonates such as SrO, CaO, Li ₂ O, MgO, Ag ₂ O or compounds of the later rare earths as well as Sc and Y.

In an embodiment of the device according to the invention, a second region is optionally additionally provided, which serves as a NO _x storage catalytic converter. In this extended embodiment, SO _x traps are thus integrated in a particle filter provided with a NO _x storage catalytic converter function, the NO _x and SO _x storage devices being spatially separated from one another. Thus, a NO _x storage radio tion and a SO _x storage function combined on a particle filter and the NO _x storage catalytic converter is protected against sulfur.

The first area, which is designed for SO _x storage, is expediently arranged upstream of the second area, which serves as a NO _x storage catalytic converter.

The first region preferably also carries one Rußoxidationsfunktion out. The use of silver and others is recommended for this at temperatures between 200 ° C and 600 ° C mobile or fluid components.

Precious metals for oxidation are preferably additionally provided in the first region. This causes an effective oxidation of SO ₂ and SO ₃ and furthermore an oxidation of NO to NO ₂ . Precious metals, in particular platinum and other redox-active compounds, such as, for example, vanadium oxides, are advantageously provided for this.

The downstream SO _x storage function can also be modified so that it lowers the burn-off temperature of the soot accumulated on the filter or is combined with a catalyst formulation lowering the burn-off temperature of the soot accumulated on the filter. The combination of soot oxidation and SO _x storage function can be achieved by successively coating the catalyst components, by mechanical mixing and subsequent coating, by combining the active components on a washcoat, by generating mixed phases, for example by means of the sol-gel process. or by supporting one component on the other so that one component serves as a washcoat.

The device according to the invention can be designed, for example, as a wall flow particle filter or as a foam or depth filter or as a combination of these particle filter types. By combining filters with SO _x storage, regeneration of filter and SO _x storage can be carried out synchronously. Furthermore, the SO _x storage is implemented in a space-saving and spatially separate manner from the NOx storage catalytic converter on a filter medium. Catalytic material can be used efficiently by using it for SO _x storage and soot oxidation.

In an expanded form, regeneration of the SO _x storage and regeneration of the NO _x storage can be carried out synchronously.

The device according to the invention enables an effective combination of a NO _x storage catalytic converter and a soot filter function, in which an SO _x trap which improves the long-term functionality of the NO _x storage catalytic converter is integrated.

Advantageous embodiments of the Invention result from the subclaims.

Further advantages and configurations the invention will become apparent from the description and the accompanying Drawing.

It is understood that the above not only mentioned and the features to be explained below in the specified combination, but also in others Combinations or alone can be used without the frame to leave the present invention.

drawing

The invention is based on an embodiment shown schematically in the drawing and is described below Described in detail with reference to the drawing.

1 shows a preferred embodiment of the device according to the invention in a sectional view.

The device shown is as a wall flow particulate filter 10 educated. This includes a gas inflow channel 12 and a gas drainage channel 14 , The structure of the particle filter 10 through a porous wall 16 defined, which effects the filter effect.

In the area of the gas inflow channel 12 is the porous wall 16 with a first area 18 coated, which performs the SO _x storage function and possibly a soot oxidation function. In the gas drainage channel 14 is the porous wall 16 with a second area 20 , namely a NO _x storage catalyst coating, provided or coated.

In operation, the exhaust gas flows into the gas inflow channel from above 12 , penetrates the first area 18 who have favourited Porous Wall 16 and the second area 20 and finally flows out of the gas discharge channel below 14 out.

Several gas inflow channels can be used 12 or several gas drainage channels 14 be arranged in parallel and next to each other alternately, the gas inlet channels on the upstream side of the filter being open and the gas outlet channels on the downstream side of the filter being open.

Claims (8)

Device for cleaning exhaust gases from a motor vehicle with a filter body, in which a first area ( 18 ) is provided, which is designed for SOx storage. Device according to Claim 1, in which a second region ( 20 ) is provided, which serves as a NO _x storage catalytic converter. The device of claim 2, wherein the first region ( 18 ) upstream to the second area ( 20 ) is arranged. Device according to one of Claims 1 to 3, in which the first region ( 18 ) also performs a soot oxidation function. Device according to one of claims 2 to 4, the gas inflow channel ( 12 ) and a gas drainage channel ( 14 ), wherein in the gas inflow channel ( 12 ) the first area ( 18 ) and in the gas discharge channel ( 14 ) the second area ( 20 ) is provided. Device according to one of claims 1 to 5, in which in the first region ( 18 ) Precious metals are provided for oxidation. Device according to one of claims 1 to 6, which as a wall-flow particle filter ( 10 ) is trained. Device according to one of claims 1 to 6, as a depth filter is trained.