Catalytic and Non-catalytic Conversion of Methane to C2 Hydrocarbons in a Low Temperature Plasma

The direct conversion of methane to C2 hydrocarbons, in a quartz tube reactor enforced by a DC corona discharge, was investigated at atmospheric pressure. The process was carried out in the presence of metal oxide catalysts of Mn/W/SiO2, Mn/W/SiO2 (tetraethyl orthosilicate, TEOS), and Mn/W/CNT (supported on carbon nanotubes). The total yield to C2 hydrocarbons in the presence of metal oxide catalysts in plasma environment was in the order of Mn/W/SiO2> Mn/W/SiO2 / TEOS> Plasma only> Mn/W/CNT. The order changes to Mn/W/SiO2>Mn/W/CNT>Plasma only> Mn/W/SiO2/ TEOS, when the selectivity and yield of ethylene is considered. The highest yield to C2 hydrocarbons was 15.8%, which was obtained by using Mn/W/SiO2 in combination with gas discharge plasma without external heating; it was lower when the same feed composition was tested over this catalyst at 825 °C. The catalyst Na2WO4/Mn2O3/SiO2 –b1, which produces the least carbon oxides, gives rise to the highest production of higher hydrocarbons and ethylene. Catalysts Na2WO4/Mn2O3/SiO2 /TEOS-b2 and Na2WO4/Mn2O3/‍CNT-b3,due to their high selectivity toward carbon oxides, show low efficiency in producing more valuable hydrocarbons.