Plasma-enhanced NOx remediation using nanosecond pulsed discharges in a water aerosol matrix

Abstract

We report nitrogen oxides remediation using a transient pulsed plasma discharge in a water aerosol gas matrix using nanosecond high voltage pulses. While there have been many studies showing highly efficient conversion of NO to NO2 using plasma-driven processes, the total removal of NOx (i.e., NO plus NO2) is severely limited by the backreaction of NO2 to NO, which is also driven by the highly reactive radical species in the plasma. By injecting water aerosol into the gas matrix, we are able to selectively drive a plasma-based reaction which minimizes the backreaction of NO2 to NO. Here, the synergistic effect of the water aerosol and plasma discharge enables enhanced NOx removal by creating OH radicals which, in turn, drive NO2 to HNO3, which is highly soluble in water. In the presence of water aerosol, the plasma discharge results in a 100% reduction in NO and a 98% reduction in total NOx. Spectroscopic evidence of the short-lived, highly reactive OH radical is obtained through plasma emission spectroscopy and the vibrational signatures of the NO2− and NO3− intermediates are observed using SERS-enhanced Raman spectroscopy. We show that the NOx remediation increases with plasma power density demonstrating the scalability of this general approach.