Complementary effects between NO oxidation of DPF and NO2 decomposition of SCR in light-duty diesel engine

This study was conducted as part of the development process of the diesel oxidation catalyst, diesel particulate filter, and selective catalytic reduction systems of old diesel vehicles for particles and NOx reduction. While SCR plays the most important role in the reduction of NOx emissions, the contribution of the DOC and DPF cannot be ignored. The conversion, generation, and reduction of NO, NO2, and N2O emissions through DOC, DPF, and SCR were tracked for use as basic data for the development of the catalyst and control logic. The results of the experiment show that NO was converted to NO2 at over 300 degrees C by Pt catalytic oxidation reaction. The highest conversion rate appeared at 450 degrees C for DOC and at 350 degrees C for DPF. NO2 was converted to NO in the operating range of 150-300 degrees C by de-oxidation reaction. Under most operating conditions, NOx reduction efficiency in SCR was maximized when the NH3 to NOx ratio was 1, but the reduction efficiency was deteriorated by excessive NO2 conversion in DOC and DPF. In SCR, NO2 decomposition without NH3 could convert NO2 to NO, showing improved NO2 reduction efficiency under some operating conditions, where NO2 was excessively converted in DOC and DPF. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.