Umicore Ag & Co Kg

Wilfried Mueller

Thomas Kreuzer

Ulrich Goebel

Stephan Eckhoff

Stephan Bremm

Christian Manfred Tomanik

Lothar Mussmann

Martin Votsmeier

Andreas Geisselmann

Ina Grisstede

Ingo Lappas

Joerg-Michael Richter

Martin Roesch

Gerald Jeske

Franz Dornhaus

Paul Spurk

Alfons Baiker

Ruediger Hoyer

Anke Woerz

Stefan Franoschek

Marek Maciejewski

Meike Wittrock

Jan-Dierk Grunwaldt

Olivier Teysset

Maria Cristina Casapu

Aflons Baiker

Stèphanie Frantz

Thomas Le Tallec

Susanne Philipp

A process which solves the problem of supplying NOin accordance with requirements by means of temperature control of the precatalyst which is decoupled from the operating state of the engine. In an associated apparatus, a precatalyst which contains at least one oxidation component and whose temperature can be controlled independently of the operating state of the engine and an active SCR stage comprising an SCR catalyst with upstream metering facility for a reducing agent from an external source are arranged in series. A particle filter can be arranged between precatalyst and metering facility. The precatalyst preferably additionally contains a nitrogen oxide storage material.

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The adherence to future legally obligatory exhaust gas limit values for diesel vehicles in Europe, North America and Japan requires not only the removal of particles but also effective removal of nitrogen oxides from the exhaust gas ('deNOx'). The 'active SCR process' is the preferred method for this. The nitrogen oxide conversions achieved by means of this process are particularly high when an optimal NO/NOratio, preferably 0.5, is set upstream of the SCR catalyst. The invention proposes a process which solves the problem of supplying NOin accordance with requirements by means of temperature control of the precatalyst which is decoupled from the operating state of the engine. In an associated apparatus, a precatalyst () which contains at least one oxidation component and whose temperature can be controlled independently of the operating state of the engine and an active SCR stage comprising an SCR catalyst () with upstream metering facility () for a reducing agent from an external source () are arranged in series. A particle filter () can be arranged between precatalyst and metering facility. The precatalyst preferably additionally contains a nitrogen oxide storage material.

The present invention relates to an exhaust-gas aftertreatment system which comprises a preferably catalytically active particle filter (wall-flow filter) which is followed in turn by a throughflow monolith (flow-through monolith) which is preferably provided with a catalytically active function. Both components have the same storage functions for gaseous substances present in the exhaust gas of internal combustion engines. The system is suitable in particular for the simultaneous removal of particles and pollutants from the exhaust gas of both predominantly lean-operated internal combustion engines and also of internal combustion engines operated predominantly with a stoichiometric air/fuel mixture. Likewise described is a process for the production and the use of such a system for exhaust-gas aftertreatment.

Exhaust-gas aftertreatment system with catalytically active wall-flow filter with storage function upstream of catalytic converter with identical storage function

Described is a method for cleaning the exhaust gases of internal combustion engines, which method is suitable for reducing harmful gases and particle emissions. Here, the exhaust gas to be cleaned is conducted, under operating conditions, with a discontinuous profile of the air ratio &#x3bb; across a wall-flow filter substrate which comprises a catalytically active coating containing one storage material. The storage material is suitable for temporarily storing one or more exhaust-gas components under certain operating conditions and releasing said exhaust-gas components again in a targeted fashion in the event of a suitable change in the operating conditions. The coating is configured such that the component has a gradient of the storage material concentration and/or of the total coating amount, with the highest concentration of the storage material in the longitudinal direction of the component being present on the inflow side. At least 60% by weight of the storage material in relation to its total amount is present in the walls between inflow and outflow ducts, and at least 50% by weight of the storage material in relation to its total amount is present in a first, inflow-side zone in the wall-flow filter substrate.

Method for cleaning internal combustion engine exhaust gases

Nitrogen oxide storage catalysts are used to remove the nitrogen oxides present in the lean exhaust gas of lean-burn engines. As a result of the stress due to high temperatures in vehicle operation, they are subject to thermal aging processes which affect both the nitrogen oxide storage components and the noble metals present as catalytically active components. The present invention provides a process with which the catalytic activity of a nitrogen oxide storage catalyst which comprises, in addition to platinum as a catalytically active component, basic compounds of strontium and/or barium on a support material comprising cerium oxide, said catalytic activity being lost owing to the thermal aging process, can be at least partly restored. The two-stage process is based on the fact that strontium and/or barium compounds formed during the thermal aging with the support material, which also comprise platinum, are recycled to the catalytically active forms by controlled treatment with specific gas mixtures.

Dual-stage method for the reactivation of thermally aged nitrogen oxide storage catalysts

To adhere to legal exhaust-gas regulations, the exhaust gases of a lean-burn engine must be freed from soot particles and nitrogen oxides. It is proposed that the cylinders of the lean-burn engine be divided into two groups which discharge their exhaust gases into two associated exhaust lines which each comprise a soot filter and which are merged at an opening-in point into a common exhaust line. The common exhaust line comprises the catalytic converter for the removal of the nitrogen oxides. By regenerating the two soot filters at different times, the exhaust-gas temperature in the common exhaust line is limited to a mean temperature between the exhaust-gas temperature of normal operation and that of regeneration operation, and the catalytic converter for the removal of the nitrogen oxides is preserved.

Method for regenerating soot filters in the exhaust gas system of a lean mix engine, and exhaust gas system therefor

Modern exhaust-gas purification systems in motor vehicles with a lean-burn engine include a starting catalyst fitted close to the engine and a main catalyst arranged in the underbody region, with both the starting catalyst and the main catalyst being formed by nitrogen oxide storage catalysts. The nitrogen oxide storage catalysts are in each case regenerated by the engine being briefly switched from lean-burn mode to rich-burn mode when the nitrogen oxide concentration in the exhaust gas downstream of the storage catalysts rises above a predetermined value. The starting catalyst is exposed to particularly high temperatures and is therefore prone to faster ageing of its nitrogen oxide storage capacity than the main catalyst. To check the nitrogen oxide storage capacity of the starting catalyst, a regeneration which is due for the catalyst system is selected in such a way in terms of its duration and the extent to which the exhaust gas is enriched that substantially only the starting catalyst is regenerated, whereas the main catalyst is not. In this arrangement, the criterion for terminating this partial regeneration is the breakthrough of rich exhaust gas through the starting catalyst. After the engine has been switched back to lean-burn mode, the time which elapses until the concentration of nitrogen oxides in the exhaust gas downstream of the catalyst requires regeneration again is measured. The measured time is a measure of the remaining nitrogen oxide storage capacity of the starting catalyst.

Method for monitoring the nitrogen oxide storage capacity of a nitrogen oxide storage catalyst used in the form of a primary catalytic converter

Soot filters for removing soot from the exhaust gas of lean-burn engines become blocked with progressive operating duration on account of the deposition of soot, and must therefore be regenerated at regular intervals. It has been found that reliable operation of the soot filter is possible only if an active regeneration is carried out from time to time by increasing the exhaust-gas temperature to the soot ignition temperature. For this purpose, an oxidation catalytic converter is usually arranged upstream of the soot filter, and the exhaust-gas temperature is increased by means of the catalytic combustion of additionally injected fuel. Here, the oxidation catalytic converter is subjected to high temperature loading and therefore ages very quickly. It has surprisingly been found that the ageing of the oxidation catalytic converter can be slowed if said oxidation catalytic converter is split into at least two separate catalytic converters and the distance between said separate catalytic converters is 2 to 30 mm.

Catalyst system and use thereof

Nitrogen oxide storage catalytic converters for purifying the exhaust gas of lean-burn engines are periodically regenerated by switching the engine from lean-burn mode to rich-burn mode. After regeneration has taken place, the engine is switched back to lean-burn mode. At this time, rich exhaust gas is still flowing in the exhaust line from the engine to the catalytic converter, which rich exhaust gas is ejected via the catalytic converter into the environment by the following, lean exhaust gas. This leads to brief emissions peaks of the rich exhaust gas constituents and impairs the level of exhaust gas cleaning which can be obtained. In order to solve said problem, it is proposed to create oxidizing conditions by injecting air upstream of the storage catalytic converter, so that the rich exhaust gas constituents still flowing in the exhaust line upstream of the storage catalytic converter can be converted at the storage catalytic converter to form non-harmful products. The proposed method can lead to a considerable improvement in exhaust gas purification in particular in the case of catalytic converters which are already impaired in terms of their storage capacity through aging, and which must be regenerated significantly more frequently than fresh catalytic converters.

Method for regenerating nitrogen oxide storage catalysts

To remove the nitrogen oxides from the exhaust gas from lean-burn engines, these engines are equipped with a nitrogen oxide storage catalyst, which has to be regenerated frequently by the engine being briefly switched to rich-burn mode. The regeneration is usually initiated when the nitrogen oxide concentration downstream of the catalyst rises above a permissible value. In this context, there is a risk of the bed temperature of the catalyst during and after regeneration being pushed into a range with incipient thermal desorption of the nitrogen oxides on account of the heat which is released during the conversion of the nitrogen oxides by the reducing constituents of the exhaust gas. This can lead to increased nitrogen oxide emission both during the regeneration itself and after the engine has been switched back to lean-burn mode. To eliminate this problem, it is proposed to divide the rich-burn mode into two rich pulses which follow one another in time, the first rich pulse being of shorter duration than the second rich pulse.

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Karben, Germany

Wilfried Mueller