AdSCR Systems (Adsorption + Selective Catalytic Reduction): Analysis of the Influence of H2O and CO2 on Low Temperature NOx Emission Reduction Performances

The removal of NOx from low-temperature diesel engine emissions still represents a big challenge in view of the upcoming more stringent worldwide regulations. In our previous studies, we proved the ability of novel AdSCR (Adsorption + Selective Catalytic Reduction) systems, based on the combination of a chemical trapping compound and a conventional SCR catalyst, to trap cold start NOx emissions and to desorb and simultaneously reduce them with ammonia at higher temperature. In the present work, we extend the investigation of Cu-CHA + BaO/Al2O3 systems under more realistic conditions, focusing on the impact of H2O and CO2. The experimental results reveal a reduction of the AdSCR system performances with respect to dry and CO2-free conditions. Despite this, the system is still able to store and reduce NOx. The NOx storage capacity on barium oxide is more affected by the presence of CO2 than by H2O. However, H2O hinders the NO oxidative activation in the zeolite cages, which is a fundamental step in order to be able to trap NOx on the storage material at low temperature. We further demonstrate that the detrimental effect of H2O can be mitigated by small amounts of NO2 in the gaseous feed or by including a 13X zeolite guard bed prior to the AdSCR bed.