Nine imidazolium-based ionic liquids were investigated as novel catalysts for methane conversion in a direct current (DC) discharge plasma reactor. The conversion of methane increased from 21.2% to 43.6% in the plasma system when the C6MIMHSO4 IL was used as a catalyst, C6MIMBF4 successfully achieved 91.0% selectivity for C-2 hydrocarbons. The results of the optical emission spectroscopy indicate that the intensity of the C-2, CH, H, C+ and C active species from methane decomposition increased when C6MIMHSO4, C6MIMCF3COO, and C6MIMBF4 were introduced into the plasma system. FTIR analysis indicates that C6MIMBF4 is steady in the DC discharge plasma. (C) 2012 Elsevier B.V. All rights reserved.