Abstract: Nitrogen oxide storage catalysts are used to remove nitrogen oxides from the exhaust gas of internal combustion engines operated predominantly under lean burn conditions. When these catalysts are used in diesel vehicles, the increased sulfur content in the fuel during operation results in poisoning of the catalyst, which is reversible at high temperatures under reduced exhaust gas conditions. In the case of conventional nitrogen oxide storage catalysts, temperatures of more than 600° C. have to be obtained for desulfurization. This is not always possible in diesel vehicles with a nitrogen oxide storage catalyst in the underbody area. The invention presents a process whose application allows the desulfurization temperature of conventional nitrogen oxide storage catalysts which comprise a platinum component and at least one nitrogen oxide storage material to be lowered. The basicity of the chemical environment of the platinum is lowered, while the nitrogen oxide storage material can remain unchanged as such.

Abstract: An emission control system for the cleaning of the exhaust gases of a lean burn engine with two or more cylinders comprises a first exhaust leg for the exhaust gases of a first group of cylinders and a second exhaust leg for the exhaust gases of a second group of cylinders. A nitrogen oxide storage catalyst is arranged in each exhaust leg. The two exhaust legs are combined downstream of the storage catalysts at a confluence to form a common exhaust leg. The common exhaust leg contains an SCR catalyst. The first and second groups of cylinders are each supplied alternately in periodic intervals with lean and rich air/fuel mixtures. Lean or rich exhaust gases are thus obtained in the combustion in the cylinders and released into the corresponding exhaust legs. Lean and rich exhaust gases are adjusted with respect to one another so as to result in a lean exhaust gas after the combination of the exhaust gases in the common exhaust leg.

Abstract: Nitrogen oxide storage catalysts are used for removing the nitrogen oxides present in the lean-burn exhaust gas of lean-burn engines. Here, the purifying action is based on the nitrogen oxides being stored in the form of nitrates by the storage material of the storage catalyst during a lean-burn operating phase of the engine and the previously formed nitrates being decomposed in a subsequent rich-burn operating phase of the engine and the nitrogen oxides which are being liberated again being reacted with the reducing exhaust gas constituents over the storage catalyst to form nitrogen, carbon dioxide and water. Storage catalysts are thermally aged by high temperatures. The aging is due to sintering of the catalytically active noble metal components of the catalyst and to formation of compounds of the storage components with the support materials.

Abstract: The invention relates to a process for coating ceramic honeycomb bodies with a coating suspension containing, in a carrier liquid, catalyst components as solids and/or in dissolved form. The honeycomb bodies have parallel flow channels running through them. The walls of the flow channels generally have an open pore structure. To coat the channel walls and in particular also the interior surfaces of the pores with the coating suspension, it is proposed that the flow channels be temporarily alternately closed and the coating suspension be forced through the open pore structure of the channel walls. The coating is subsequently dried and calcined. To close the flow channels, it is possible to use thermally or chemically decomposable or soluble compositions which are decomposed or dissolved either during calcination or by means of a subsequent chemical treatment. The coated honeycomb bodies are preferably used for the purification of exhaust gases from automobiles.

Abstract: The invention provides a process for reducing the amounts of carbon monoxide, hydrocarbons and soot particles in the lean exhaust gas from an internal combustion engine using a particle filter, wherein the soot particles have a soot ignition temperature TZ and the particle filter is regenerated from time to time by raising the temperature of the particle filter to above the soot ignition temperature and burning the soot particles, wherein the temperature of the filter is increased to the temperature required to initiate soot ignition by burning additional fuel on the catalytic coating when the exhaust gas back pressure reaches a predetermined value. The process is characterised in that the particle filter is provided with a catalytic coating comprising a first group of components for reducing the ignition temperature of soot, said first group of components contains at least one oxygen storage component and at least one platinum group metal selected from the group consisting of platinum, palladium and rhodium.

Abstract: 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.

Abstract: The present invention relates to a catalyst for the purification of exhaust gases from an internal combustion engine, which comprises a catalytically active coating on an inert ceramic or metal honeycomb body, said coating comprising at least one platinum group metal selected from the group consisting of platinum, palladium, rhodium and iridium on a fine, oxidic support material. As an oxidic support material, the catalyst comprises a low-porosity material on the basis of silicon dioxide that comprises aggregates of essentially spherical primary particles having an average particle diameter of between 7 and 60 nm.

Abstract: 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.

Abstract: 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.

Abstract: The invention proposes a particulate filter having a catalytic coating which contains two catalysts arranged one behind the other. The first catalyst is located in the gas inlet region of the filter and contains a palladium/platinum catalyst. The second catalyst is arranged downstream of the first catalyst and preferably contains platinum alone as catalytically active component. The combination of these two catalysts provides the coated filter with a good ageing stability and resistance to sulphur poisoning.

Abstract: Coating a wall-flow filter with a catalytically active coating generally increases the exhaust-gas backpressure in the filter. The increase in the exhaust-gas backpressure is particularly pronounced if a slurry of fine-particle catalyst materials is used for the coating operation. The increase in the exhaust-gas backpressure can be restricted to a tolerable level if, prior to the coating operation, the slurry is so finely milled that virtually the entire mass of the catalyst materials is introduced into the pores of the filter and deposited on the inner surfaces of the pores. This is the case if the d90 diameter of the particles in the slurry is reduced to below 5 ?m by milling.

Abstract: A stream of exhaust gases from the combustion of hydrocarbon-containing fuels with a variable temperature can be produced by dividing the exhaust gases into two separate part-streams, cooling one part-stream and then combining the two part-streams again. The temperature of the exhaust-gas stream which has been combined again can be set to between the temperature of the combustion of the hydrocarbon-containing fuels and the temperature of the cooled exhaust-gas part-stream by corresponding throttling of the two part-streams before they are brought together again. The exhaust-gas stream produced in this way is preferably used for the defined ageing of automotive exhaust catalysts. In this context, it is particularly advantageous that the change in the temperature of the exhaust-gas stream has no influence on its air/fuel ratio.

Abstract: Nitrogen oxide storage catalysts are used for removing the nitrogen oxides present in the lean-burn exhaust gas of lean-burn engines. Here, the purifying action is based on the nitrogen oxides being stored in the form of nitrates by the storage material of the storage catalyst during a lean-burn operating phase of the engine and the previously formed nitrates being decomposed in a subsequent rich-burn operating phase of the engine and the nitrogen oxides which are being liberated again being reacted with the reducing exhaust gas constituents over the storage catalyst to form nitrogen, carbon dioxide and water. Storage catalysts are thermally aged by high temperatures. The aging is due to sintering of the catalytically active noble metal components of the catalyst and to formation of compounds of the storage components with the support materials.

Abstract: A nitrogen oxide storage material which is based on storage compounds of elements selected from the group consisting of magnesium, calcium, strontium, barium, the alkali metals, the rare earth metals and mixtures thereof and has a homogeneous magnesium-aluminium mixed oxide doped with cerium oxide as support material for the storage compounds is described. Nitrogen oxide storage catalysts using this storage material display a broad working range, a high storage efficiency and good ageing resistance.

Abstract: An oxygen storage material comprising cerium oxide and at least one second oxide of a metal M1 is disclosed as well as a process for manufacturing the material and the use of this material in an exhaust gas cleaning catalyst. In a preferred embodiment the oxygen storage material comprises particles from a Ce/M1 mixed oxide solid solution coated with an oxide of another metal M2. Metal M1 e.g. can be calcium or zirconium while metal M2 most preferably is aluminum.

Abstract: The fuel qualities for vehicles differ, for example, in Europe on a regional basis. This applies in particular to the sulphur content of the fuel. If vehicles with modern lean engines or with diesel engines which are equipped with nitrogen oxide storage-type catalytic converters in order to reduce the nitrogen oxide content in their exhaust gas pass through regions with a sulphur content in the fuel which is above the sulphur content which is specified for the vehicle, the engine controller will correspondingly frequently initiate desulphurization of the storage-type catalytic converter after the vehicle has been refuelled with this fuel. Any desulphurization entails an increased level of fuel consumption and greater ageing of the catalytic converter. It is proposed to avoid these adverse effects in that in lean motors the engine controller switches to stoichiometric operation in such a case, and in a diesel engine said engine controller prevents the desulphurization.

Abstract: The preparation of finely divided, alkali metal-containing metal oxide powders which contain at least one alkali metal and at least one further metal from the group consisting of the transition metals, the remaining main group metals, the lanthanides and actinides is described. Precursor compounds of these components are introduced in solid form or in the form of a solution or a suspension into a pulsation reactor having a gas flow resulting from a flameless combustion and partly or completely converted into the desired multicomponent metal oxide powder.

Abstract: An exhaust gas treatment unit for the selective catalytic reduction of nitrogen oxides under lean exhaust gas conditions which contains at least one catalyst with catalytically active components for selective catalytic reduction (SCR components). The exhaust gas treatment unit is characterised in that the catalyst also contains, in addition to SCR components, at least one storage component for nitrogen oxides (NOx components).

Abstract: This invention relates to a method and a corresponding apparatus for coating open-pored bodies with at least one coating suspension. In particular, the coating suspension has solids and solutes in a liquid medium in a quantity in wet state which is to correspond to at least a required target quantity. The coating operation has a variation in the applied wet coating quantity from one body to the other. The method according to the invention is characterized by the steps of: coating the body with an actual quantity of the coating suspension, which is always larger than the required target quantity taking the variation of the coating operation into account, determining the difference between the actual quantity and the required target quantity, and reducing the difference between actual quantity and target quantity by removing still wet coating suspension.

Abstract: The present invention is directed to a particle filter to remove soot from the exhaust gas of a diesel engine. The particle filter contains a catalytically active coating on a filter body to accelerate bum-off during a regeneration phase of the soot particles collected on the filter. The particle filter comprises a catalytic coating containing compounds of barium, compounds of magnesium, and at least one element of the platinum group metals. The invention is further directed to a process for accelerated combustion of soot particles collected on the filter from lean exhaust gas of a diesel engine in which the soot particles have a soot ignition temperature and the particle filter is actively regenerated from time to time by raising the temperature of the particle filter above the soot ignition temperature and burning off the soot particles.