Methane oxidative conversion pathways in a dielectric barrier discharge reactor—Investigation of gas phase mechanism

Non-thermal plasma, over the past few years, is being investigated for methane conversion. In order to improve the efficiency, combined plasma and catalyst is being explored to exploit possible synergetic effects. The present paper investigates plasma assisted methane conversion in gas phase by partial oxidation at low energy density (80–200 kJ/mol CH4) and low reactor temperatures (130–140 °C). Although non-thermal plasma has the inherent advantage of initiating reactions, a disadvantage is the unfavorable selectivity to the desired product. The investigation attempts to identify the plasma initiated chemical reaction pathways by combining experiments and kinetic modeling. Sensitivity analysis indicates reaction intermediates leading to formation of oxygenates as an alternative oxidation pathway at the investigated temperatures (T < 200 °C). The selectivity for synthesis gas formation could be increased by partial oxidation at higher CH4/O2 ratios. Combined partial oxidation and steam reforming was as well investigated in order to increase H2 concentration. Isotopes were used in order to identify reaction pathways for the case of steam reforming experiments. However, experiments at lower energy density indicate negligible steam conversion. At lower temperatures, the input plasma energy is primarily used for CH4/O2 conversion.