Abstract: An internal combustion engine with a reducing agent-generating unit for generation of an H2-containing and/or NH3-containing reducing gas, which can be added to an exhaust gas line upstream from an NOx reducing catalytic converter, and a procedure for the operation of such an internal combustion engine are proposed. The reducing agent-generating unit has an NOx generation step and an H2 generation step in serial arrangement. NH3 is formed at least temporarily by chemical reaction by the reducing agent-generating unit from NOx produced in the NOx generation step. The invention is applicable in motor vehicles, especially in passenger vehicles with Diesel engines.