Arrangement for reducing nitrogen oxides in exhaust gases

摘要

An arrangement and method for reducing the nitrogen oxide content in the exhaust gas of an internal combustion engine with the aid of ammonia and/or ammonia-releasing reduction agents, whereby ammonia and/or ammonia-containing reduction agent is added to the exhaust gas stream upstream of a catalyst combination composed of an SCR catalyst and a subsequent NH3-oxidation catalyst in such a way that a homogeneous mixture of exhaust gas and ammonia is present upstream of the SCR catalyst. To optimize the reaction or conversion of nitrogen oxides, disposed downstream of the combination of a first SCR catalyst and a first NH3-oxidation catalyst is at least one second catalyst having SCR activity in order in this way to reduce the nitrogen oxides formed at the first NH3-oxidation catalyst due to insufficient selectivity of the catalyst to nitrogen with not yet oxidized NH3.