Method for the catalytic removal of nitrogen oxides from exhaust gases by means of a reducing agent

A method of removing nitrogen oxides contained in exhaust gases with a temperature from 0.degree.-600.degree. C. comprising treating said exhaust gases with a reducing agent in the presence of a nitrogen oxide reducing catalyst having active centers at a stoichometric ration between the concentration of reducing agent and the initial concentration of nitrogen oxide, dosing the reducing agent into the exhaust gas to be treated in a controlled discontinuous manner in such a manner to avoid adsorption of the reducing agent and blocking of the active centers of said catalyst by said reducing agent, said dosing being in pulses t.sub.A of 0.01 to 15,000 sec. duration with stop intervals t.sub.Z therebetween of 0.1 to 15,000 sec. duration.