Plasma-Assisted Ammonia Decomposition and Oxidation

We studied the effects of non-thermal plasma on ammonia decomposition and oxidation. To this end, we designed a dielectric barrier discharge (DBD) flow reactor and interfaced it to an existing molecular-beam mass spectrometer (MBMS). We measured product species downstream of the plasma zone at low pressure (20 Torr). For studying ammonia decomposition, we supplied premixed ammonia and argon (Ar) at room temperature to the flow reactor and observed the production of nitrogen (N2) and hydrogen (H2). The H2 yield increased with an increased plasma peak voltage, a longer residence time in the DBD flow reactor, and a higher ammonia concentration in the feed gases. To study ammonia oxidation, we supplied a premixed mixture of ammonia, oxygen (O2), and argon at room temperature to the flow reactor. Ammonia oxidation by plasma produces mainly water (H2O) and nitrogen (N2). Additionally, we detected nitric oxide (NO) under lean conditions. The mole fraction of NO emission decreases as the plasma peak voltage increases or the residence time in the DBD flow reactor becomes longer. In other words, NO production is attenuated with stronger plasma effects, indicating that a plasma-produced species may prohibit NO formation, or that formed NO is reacting away more quickly.