Non-thermal plasma assisted methane oxidation inside a DBD reactor: Effect of monometallic catalyst on energy efficiency and CO2 selectivity

The oxidation of methane was studied in a co-axial dielectric barrier discharge (DBD) quartz tube reactor at room temperature and atmospheric pressure. Methane oxidation was investigated in two reactor configurations: an empty DBD reactor and a packed-bed DBD reactor containing various oxidation catalysts (Co/Al2O3, Cu/Al2O3, Fe/Al2O3, Pt/Al2O3, and Pd/Al2O3). Methane oxidation was examined at plasma power levels ranging from 20 to 40 W. In the empty DBD reactor, methane conversion was initiated at 23 W plasma power. Methane conversion increased with increasing plasma power due to generation of more active species. The main methane oxidation products were CO and CO2. Both CO2 selectivity and energy efficiency improved with increasing plasma power. However, methane conversion, CO2 selectivity, and energy efficiency declined as the gas flow rate was increased due to the reduced residence time of gases inside the plasma discharge zone. In the packed-bed DBD reactor, methane conversion was lower than in the empty reactor due to the reduced residence time of gases inside the plasma discharge zone. The presence of catalyst increased the plasma power requirements for methane conversion. Among the catalysts, Co/Al2O3 and Cu/Al2O3 catalysts exhibited higher methane conversion at lower plasma power (<30 W), while Pd/Al2O3 catalyst demonstrated higher methane conversion at higher plasma power (>35 W). The presence of catalysts generally improved CO2 selectivity, with noble metal catalysts achieving above 95 % CO2 selectivity across all plasma power levels studied. Despite the higher plasma power requirements in packed-bed DBD, both Pd/Al2O3 and Co/Al2O3 improved energy efficiency compared to the empty reactor.