a structured catalyst for selective reduction of nitrogen oxides with ammonia using an ammonia - supplying compound . the catalyst is preferably used for exhaust gas treatment of diesel vehicles powered by diesel motors . the catalyst is characterized by the fact that it contains a reduction catalyst for selective reduction of nitrogen oxides with ammonia and a hydrolysis catalyst for the hydrolysis of urea , where the hydrolysis catalyst is applied in the form of a coating onto the reduction catalyst . by this arrangement of the two catalytic functions in one catalyst the exhaust gas system can be made very compactly and space saving . moreover , advantageous synergistic effects result from the direct contact of the hydrolysis catalyst and the reduction catalyst .