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

Abstract

We report on factors influencing the specific energy costs of producing NOx from 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 Al2O3 catalyst 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 NOx production 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.