The topics on conversion and utilization of methane and carbon dioxide are important issues in tackling the global warming effect from the two greenhouse gases. In the present study, pure plasma and plasma catalytic activation of methane and carbon dioxide were investigated for syngas production. For pure plasma process, the effects of discharge power, CH4/CO2 ratios in the feed, total flow rate, as well as the concentration of the balanced gas of Ar were studied. Ar in the feed has great effects on the conversion and the stability of the reaction. At 120 degrees C and atmospheric pressure, the conversion of CH4 increased from 39% to 56% and that of CO2 increased from 23% to 30% when the Ar content in the feed increased from 0% to 50%, whereas Ar showed little effect on the H-2/CO ratios in the products. Moreover, the conversions of CH4 and CO2 remained unchanged within the testing hours in the presence of 50% of Ar, which was contrastive with those obtained without Ar in the feed. When Cu-Ni/Al2O3 catalyst was filled in the discharge gap at 450 degrees C, the synergism between the catalyst and dielectric-barrier discharge (DBD) plasma was achieved. Conversions of CH4 for plasma alone, plasma-catalysis and catalysis alone were 13%, 69% and 10%, respectively. Selectivities to CO and H-2 under the plasma-catalytic process were, respectively, 76% and 57%. (C) 2009 Published by Elsevier B.V.