The impact of light and heavy hydrocarbons on the NH3-SCR activity of commercial Cu- and Fe-zeolite catalysts

Low temperature operation of NH3-SCR systems for NOx abatement in lean burn and Diesel engines poses new demanding challenges due to the necessity of solving issues related to poor catalyst activity, urea injection management and system control. A typical example of these problems is represented by unconverted hydrocarbons (HCs) slip (e.g. during cold start or long idling) onto the SCR catalyst leading to a subsequent decrease of the DeNOx activity. In the present work, a detailed evaluation of the impact of different hydrocarbons (namely C3H6 and C10H22) on the performances of two new generation commercial zeolite SCR catalysts promoted with Fe and Cu is carried out by means of transient response method (TRM) experiments. Particular attention is devoted to elucidate the interaction between HCs and the typical constituents of SCR feed such as NH3, NO, NO2, O-2 and H2O and their influence on the overall reactivity, in order to possibly clarify the associated mechanistic steps.