A new method for the model-based optimization of the time-dependent urea dosing for SCR catalysts (selective catalytic reduction) is presented. Optimized dosing profiles are computed for two different catalysts (Fe- and Cu zeolite). It is shown that the relative performance of the two catalysts depends on the choice of the dosing profile. This means that a meaningful comparison between different catalysts is only possible if each catalyst is tested with an individually optimized urea dosing strategy.