Specific energy cost for nitrogen fixation as NO_xusing DC glow discharge in air

We report on factors influencing the specific energy costs of producing NO_xfrom pin-to-pin DC glow discharges in air at atmospheric pressure. Discharge current, gap distance, gas flowrate, exterior tube wall temperature and the presence and position of activated Al₂O₃catalyst powder were examined. The presence of heated catalyst adjacent to the plasma zone improved energy efficiency by as much as 20% at low flows, but the most energy efficient conditions were found at the highest flowrates that allowed a stable discharge (about 10-15 l min^-1). Under these conditions, the catalyst had no effect on efficiency in the present study. The lowest specific energy cost was observed to be between about 200-250 GJ/tN. The transport of active chemical species and energy are likely key factors controlling the specific energy costs of NO_xproduction in the presence of a catalyst. Air plasma device design and operating conditions must ensure that plasma-generated active intermediate chemical species transport is optimally coupled with catalytically active surfaces.