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The selective catalytic reduction (SCR) of nitrogen oxides (NOx) is the most promising technique to meet prospective emission regulations of diesel-driven commercial vehicles. Due to the installation of SCR- systems downstream of both the oxidation catalyst and the particulate filter, the relatively long light-off phase after engine startup limits the overall efficiency of reducing emissions. Another challenge is the fact that, once the light-off temperature is achieved it must be maintained. In particular, the operation of urban busses with highly transient load profiles involves many phases of idling with low exhaust gas temperatures (e.g., during bus stops and/or at traffic lights). In contrast to previous studies, these investigations combine properties of catalysts determined in the course of experiments with the simulation of real operational profiles.