Interaction between soot particles and NOx during dielectric barrier discharge plasma remediation of simulated diesel exhaust

Plasma remediation is being investigated as a means to remove NOx from combustion effluent and from diesel exhausts in particular. Soot particles are inevitably present in actual exhausts and may, through heterogeneous chemistry, affect the remediation process. In this article, a computational investigation of the effect of soot on the plasma chemistry of NOx removal in a simulated diesel exhaust processed in a dielectric barrier discharge reactor is presented using a zero-dimensional global-kinetics simulation. A surface chemistry model is employed to describe soot oxidation by O and OH radicals, and soot-NOx interactions. The NOx chemistry may be substantially affected by the reactions at the soot surface. In particular, for soot particles having densities of 108 cm−3 and diameters of 100 nm, significant increases of NO are obtained when taking into account NO2→NO conversion on the soot surface. Heterogeneous reaction of NO2 also results in an increase in the gas-phase OH density which results in the increased formation of HNO2, thereby adding to the NOx remediation. NO2→NO heterogeneous conversion also results in an increase of CO and a subsequent reduction of the soot mass. The mechanism for soot-NOx interactions depends on the deactivation of active hydrocarbon radicals on the soot.