Process for selective catalytic reduction of exhaust gases from Diesel engines

Process for selective catalytic reduction of exhaust gases from motor vehicle diesel engines with timed addition of NH3 or NH3-releasing substances, the timed superstoichiometric NH3 addition being controlled in such a manner that the addition, after its start, is only terminated when, at a defined site in the catalyst bed, a high NH3 concentration, which is established as a threshold value, is obtained in the gas phase and is only started again when the NH3 stored in the catalyst has been substantially consumed by the reaction, this time point being determined by calculation by approximation of the NOx, produced by the engine over the period since the beginning of metering or alternatively from the end of metering, from the engine characteristics and operating time and taking into account the average separation efficiency.