Boosting NOxremoval by perovskite-based catalyst in NSR-SCR diesel aftertreatment systems

Abstract

A detailed analysis of the DeNOx 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 (TNSR/TSCR = 150-450 °C) and H2 concentration (CH2 = 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 NOx 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 NOx slipping NSR catalyst in the SCR system placed downstream. The novel NSR-SCR system shows N2 yields above 75% in a wide working window (TNSR/TSCR = 175-425 °C and CH2 = 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 NOx 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 NOx removal by NSR and NSR-SCR technologies.