Experimental and modelling study of the ammonia-SCR process for NOx abatement from mobile sources

In this Study, experimental tests have been carried out in order to comprehend the activity of Cu-CHA in comparison to more conventional SCR catalysts, e.g. V-based catalysts. The first part of the study covered Standard SCR experiments over these SCR catalysts. Moreover, a mechanistic study has been carried out, aiming at quantitatively developing and validating a kinetic model for NO oxidation on Cu-CHA catalysts, which has been proposed to be very a important step in the SCR chemistry. Firstly, the detailed steps of NO oxidation are proposed and consequently, the rate equation has been derived. Secondly, a systematic set of steady state kinetic runs have been carried out over a commercial Cu-CHA catalyst to address the effects of different operating variables on the rate of NO oxidation. Lastly, the results of these experiments have been employed to estimate the intrinsic rate parameters in the proposed kinetic mechanism. The model predictions were found truthfully in accordance with the experimental results. This mechanistic model seems therefore a step forward towards a better understanding of the SCR-DeNOx activity of Cu-CHA. This NO oxidation model is discussed in the second part of my PhD thesis. In the third part of the thesis extensive operando spatially and time-resolved XAS measurements have been carried out in order to elucidate the interaction of different species in the SCR reactions. This work was performed in collaboration with Prof. Jan-Dierk Grunwaldt at the Karlsruhe Institute of Technology (KIT). Various trends have been observed for the NH3 interaction with the active Cu sites on different loadings of Cu-SSZ-13 at low and high temperatures. Such trends supports the idea of two different dominant active sites for NH3-SCR at low and high temperatures. The nature of the active Cu sites in a wide T-range has been studied by detailed XANES and EXAFS analysis. The integration of the SCR and DPF units (SDPF) in the exhaust aftertreatment system of diesel engines is an innovative solution to decrease diesel engine emissions down to the upcoming regulated levels, which is the topic of the fourth part of my PhD thesis. In this work, the capability of a commercial SDPF, which is a DPF monolithic converter with Cu-CHA coating in the DeNOx activities has been comprehensively studied. Standard and Fast SCR, ammonia oxidation and ammonia TPD experiments have been performed on the sample. Moreover, the effect of aging as a function of time and temperature has been evaluated, employing six aged SDPF samples. The fifth part of the PhD study is dedicated to another important component of a diesel aftertreatment, i.e. the Diesel Oxidation Catalyst (DOC). As the diesel engines becomes more fuel efficient, the temperature of the tailpipe becomes lower and therefore the cold start emissions turn out to be a more significant problem. In this part of the work, we have focused on the water thermal effect on a commercial DOC in the T-range of engine cold start. The thermal effect of water vapor adsorption on DOC, which causes a strong temperature increase in the DOC monolith, and the impact of the aging process were extensively studied. Finally, the last part of the PhD work has focused on the production of pure gaseous NO. This study has investigated the feasibility of using a cheap, relatively easy and sustainable process of pure gaseous NO production according to a catalytic reaction well known in Lean DeNOx aftertreatment catalysis. To this end, a BaO/γ−Al2O3 catalyst was prepared in the laboratory of LCCP and used eventually for further investigations.