SYSTEM TO REDUCE THE TOXICITY OF EXHAUST ENGINE GASES USING A SELECTIVE CATALYTIC REDUCTION CATALYST

摘要

1. A method for reducing the toxicity of exhaust gases (OG) containing nitrogen oxides and hydrocarbons of diesel engines, which consists in that! (a) ammonia or a decomposition compound is added to the exhaust gas stream containing nitrogen oxides and hydrocarbons from a source not related to the exhaust tract,! (b) an exhaust gas stream containing nitrogen oxides, hydrocarbons and ammonia or a compound decomposing to it is passed over the first selective catalytic reduction catalyst (SCR) located on the inlet side, which effectively catalyzes the compression of nitrogen oxides with ammonia in the temperature range from 300 to 500 ° C and at least partially oxidizes the hydrocarbons in the exhaust gas, and! (c) exhaust gases from step (b) are passed over a second SCR catalyst located on the downstream side, which efficiently catalyzes the compression of nitrogen oxides with ammonia in the temperature range from 150 to 400 ° C and simultaneously accumulates excess ammonia. ! 2. The method according to claim 1, characterized in that the exhaust gas stream containing nitrogen oxides and hydrocarbons is passed over an oxidation catalyst, which catalyzes the oxidation of at least part of the nitrogen contained in the nitrogen oxides, before adding ammonia or a compound decomposing to it in step (a) NO to NO2. ! 3. The method according to claim 2, characterized in that the ratio of NO2 / NOx in the exhaust gas is changed in such a way that it is in the exhaust gas stream before it is passed in step (b) over the first SCR catalyst located on the inlet side from 0.3 up to 0.7. ! 4. The method according to claim 1, characterized in that ammonia or a compound decomposing to it is added in step (a) to the sweat�