Detailed thermal and chemical characterization of ammonia dissociation and oxidation in a plasma-stirred reactor

This study explores the effects of plasma property and composition parametric variation on plasma temperature and various output species. A non-equilibrium nanosecond-pulsed high-frequency dielectric barrier discharge (DBD) plasma was employed in this work. Targeting the “second positive system” of nitrogen (C3Πu -> B 3Πg) optical emission spectroscopy (OES) was utilized to determine the rotational and the vibrational temperature of N₂ present in the plasma. Specific energy input (SEI) strongly influenced rotational temperature, varying from 430 to 900 K for SEI of 0.14 to 1.5 J/cm³, compared to vibrational temperature, which showed no definitive trend. Ammonia conversion and hydrogen production were quantified using Fourier transform infrared (FTIR) spectroscopy and gas chromatography (GC), respectively. SEI again was determined as the driving factor of NH3 dissociation and H₂ production with pulse repetition frequency being the most efficient method to increase conversion efficiency compared to applied voltage. By varying the reactor’s operating conditions these methods were used to identify the effects of wide-ranging conditions on product yield, species distributions, and efficiency of plasma-assisted dissociation and oxidation of ammonia mixtures.