Process for reducing agent control in an exhaust gas aftertreatment system

A method of reducing agent control in an exhaust gas aftertreatment system of a combustion engine with an exhaust gas pipe in which in the direction of flow of the exhaust gas there is an SCR catalyzer, whereby a reducing agent generating system has an NOx and CO/H2 generating unit, an oxidation catalyzer, and a combined NOx storage/ammonia generating unit in a standard gas path of the reducing agent generating system, the method comprising:

• introducing ammonia as a reducing agent for a reduction of nitric oxides before the SCR catalyzer of the reducing agent generating system and directing, at least temporarily, precursor materials for generation of ammonia to the NOx and CO/H2 generating unit through a fuel feed and an air feed, wherein a CO/H2 reducing agent stream is temporally modulated during a rich phase with λ<1 serving as a reducing phase for the NOx storage/ammonia generating unit, whereby a CO/H2 concentration is primarily held constant at a high level.