Boosting NO x Removal by Perovskite-Based Catalyst in NSR–SCR Diesel Aftertreatment Systems

A detailed analysis of the DeNO x activity of the novel 0.5% Pd-30% La0.5Ba0.5CoO3/Al2O3 formulation in its application to the single-NSR and combined NSR–SCR systems is carried out using response surface methodology (RSM). The complete operational map of the NSR and NSR–SCR configurations has been obtained for any combination of reaction temperature in each catalytic bed (T NSR/T SCR = 150–450 °C) and H2 concentration (C H2 = 1%–4%) in the feed stream during the rich period. In the NSR–SCR configuration, a 4% Cu/SAPO-34 catalyst is placed downstream of the perovskite-based formulation as a SCR formulation. On the basis of the response surface curves of single-NSR system, the operational conditions have been tuned in order to maximize the NO x to N2 conversion of the coupled NSR–SCR system, minimizing the NH3 and N2O productions. The H2 concentration and reaction temperature of the NSR system must be controlled to generate a stoichiometric amount of NH3 to reduce the NO x slipping NSR catalyst in the SCR system placed downstream. The novel NSR–SCR system shows N2 yields above 75% in a wide working window (T NSR/T SCR = 175–425 °C and C H2 = 2%–4%). Specifically, the maximum N2 yield is as high as 92%, when NSR and SCR catalysts were working at 300 °C with a H2 concentration of 3%. Under these conditions NH3 slip and N2O production were nearly zero. In fact, the NO x removal efficiency and hydrothermal stability of NSR and NSR–SCR systems based on 0.5% Pd-30% La0.5Ba0.5CoO3/Al2O3 and model NSR catalysts (1.5% Pt-15% BaO/Al2O3) are comparable. Taking into account the significant decrease of noble metal content, these results demonstrate that the developed catalyst can be considered as a promising alternative for NO x removal by NSR and NSR–SCR technologies.