摘要:
In exhaust gas purification units for decreasing nitrogen oxides in lean-burn exhaust gas of internal combustion engines by selective catalytic reduction by means of ammonia, introduction of excess ammonia leads to undesirable emissions of unused ammonia. These emissions can be decreased by means of ammonia barrier catalysts. In the ideal case, ammonia is oxidized to nitrogen and water by these catalysts. These require additional space in the exhaust gas purification unit which may have to be taken away from the space provided for the SCR main catalyst. In addition, the use of such ammonia barrier catalysts can result in overoxidation of the ammonia to nitrogen oxides.To overcome these disadvantages, a catalyst containing two superposed layers is proposed for the removal of nitrogen-containing pollutant gases from diesel exhaust gas. The lower layer contains an oxidation catalyst and the upper layer can store at least 20 milliliters of ammonia per gram of catalyst material. This catalyst displays reduced ammonia breakthrough at good SCR conversions in the low-temperature range. It can be used as SCR catalyst having reduced ammonia breakthrough or as ammonia barrier catalyst.
摘要:
The reductive removal of nitrogen oxides from the exhaust gas from internal combustion engines operated predominantly under lean conditionstakes place in a selective catalytic reduction (SCR) of the nitrogen oxides by means of ammonia or a compound which can be decomposed into ammonia as reducing agent. Conventional SCR catalysts typically have a relatively narrow working temperature window, usually 350° C. to 520° C., in which good nitrogen oxide conversions can be achieved with sufficient selectivity. SCR catalyst formulations whose working window is in the temperature range from 150° C. to 350° C. generally not be used at higher temperatures since they oxidize the ammonia required as reducing 18 agent to nitrogen oxides at above 350° C. To cover the entire exhaust gas temperature range typical of vehicles having been operating internal combustion enginesextending from 200° C. to 600° C., it has therefore mostly been necessary to use complicated exhaust gas systemscontaining a plurality of catalysts having different working temperature ranges. Disclosed is a structured SCR catalyst whose working range extends over a significantly broader temperature window and by means of which complicated exhaust gas units can be considerably simplified, with a saving of components.
摘要:
The reductive removal of nitrogen oxides from the exhaust gas from internal combustion engines operated predominantly under lean conditions takes place in a selective catalytic reduction (SCR) of the nitrogen oxides by means of ammonia or a compound which can be decomposed into ammonia as reducing agent. Conventional SCR catalysts typically have a relatively narrow working temperature window, usually 350° C. to 520° C., in which good nitrogen oxide conversions can be achieved with sufficient selectivity. SCR catalyst formulations whose working window is in the temperature range from 150° C. to 350° C. generally not be used at higher temperatures since they oxidize the ammonia required as reducing 18 agent to nitrogen oxides at above 350° C. To cover the entire exhaust gas temperature range typical of vehicles having been operating internal combustion engines extending from 200° C. to 600° C., it has therefore mostly been necessary to use complicated exhaust gas systems containing a plurality of catalysts having different working temperature ranges. Disclosed is a structured SCR catalyst whose working range extends over a significantly broader temperature window and by means of which complicated exhaust gas units can be considerably simplified, with a saving of components.
摘要:
The invention relates to a catalyst arrangement for purifying the exhaust gases of internal combustion engines operated under lean conditions. It is proposed that a thinwalled, porous carrier be coated on one side with a nitrogen oxide storage catalyst and on the other side with an SCR catalyst. When the exhaust gas is passed through the catalytic coatings and the support material, a significant improvement in the nitrogen oxide conversion is achieved compared to a series arrangement of the catalysts on separate carriers. Wall flow filters have been found to be useful as thin-walled carriers.
摘要:
The invention relates to a catalyst arrangement for purifying the exhaust gases of internal combustion engines operated under lean conditions. It is proposed that a thinwalled, porous carrier be coated on one side with a nitrogen oxide storage catalyst and on the other side with an SCR catalyst. When the exhaust gas is passed through the catalytic coatings and the support material, a significant improvement in the nitrogen oxide conversion is achieved compared to a series arrangement of the catalysts on separate carriers. Wall flow filters have been found to be useful as thin-walled carriers.
摘要:
A catalytically active diesel particulate filter with ammonia trap action is presented, which, in addition to an oxidation-active coating (2), comprises a coating (1) which is catalytically active in the SCR reaction. By means of this inventive diesel particulate filter, it is possible to make exhaust gas aftertreatment systems for removing nitrogen oxides and particulates from the exhaust gas of lean engines considerably simpler and less expensive.
摘要:
An exhaust gas purification system (method and device) for the treatment of diesel exhaust gases containing nitrogen oxides and hydrocarbons is disclosed, which comprises the addition of ammonia or of a compound decomposable to ammonia into the exhaust gas stream and the subsequent leading of the exhaust gas stream over two successively arranged SCR catalysts with different properties and compositions. Both SCR catalysts are free of vanadium compounds and only the downstream SCR catalyst contains zeolite compounds. The exhaust gas purification system according to the invention is characterized by good “kick-off” behavior at low temperatures and a simultaneously high conversion performance over a wide temperature range.
摘要:
An exhaust gas purification system (method and device) for the treatment of diesel exhaust gases containing nitrogen oxides and hydrocarbons is disclosed, which comprises the addition of ammonia or of a compound decomposable to ammonia into the exhaust gas stream and the subsequent leading of the exhaust gas stream over two successively arranged SCR catalysts with different properties and compositions. Both SCR catalysts are free of vanadium compounds and only the downstream SCR catalyst contains zeolite compounds. The exhaust gas purification system according to the invention is characterized by good “kick-off” behavior at low temperatures and a simultaneously high conversion performance over a wide temperature range.
摘要:
A catalytically active diesel particulate filter with ammonia trap action is presented, which, in addition to an oxidation-active coating (2), comprises a coating (1) which is catalytically active in the SCR reaction. By means of this inventive diesel particulate filter, it is possible to make exhaust gas aftertreatment systems for removing nitrogen oxides and particulates from the exhaust gas of lean engines considerably simpler and less expensive.
摘要:
Selective catalytic reduction with ammonia or a compound that decomposes to ammonia is a known method for the removal of nitrogen oxides from the exhaust gas of primarily lean-burn internal combustion engines. The vanadium-containing SCR catalysts that have long been generally used for this are characterized by a good conversion profile. However, the volatility of vanadium oxide can, at higher exhaust gas temperatures, lead to the emission of toxic vanadium compounds. Zeolite-based SCR catalysts, which are used in particular in discontinuous SCR systems, constitute a very cost-intensive solution for the problem.A method is proposed by which a homogeneous cerium-zirconium mixed oxide is activated for the SCR reaction in a defined manner by the introduction of sulphur and/or transition metal. Using this method, a highly active, ageing-resistant SCR catalyst is provided, which represents a vanadium-free, cost-effective and high-performance alternative to the existing SCR catalysts and is suitable in particular for use in motor vehicles.