This paper describes the enhancement of CO2 methanation using dielectric barrier discharge (DBD) on Ru catalyst under atmospheric conditions. The DBD plasma leads to increased deoxygenation of CO2, which is decomposed into CO. Subsequently, the Ru catalyst activates the methanation in the DBD plasma at atmospheric conditions. The effect of the discharge frequency of the DBD plasma and the H-2/CO2 mixture ratio on the CO2 conversion and CH4 selectivity is investigated. The CO2 conversion and CH4 selectivity rapidly increase at a discharge frequency above 2.5 kHz, and reach 23.20% and 95.02%, respectively, when the H-2/CO2 molar ratio is 7. CO2 methanation and deoxygenation are simultaneously enhanced by adding Ar. Optical emission spectroscopy is used for the plasma diagnostics in the CO2 methanation process. The optical emission spectra of the gamma-Al2O3 and Rui/gamma-Al2O3 catalysts are measured to investigate the effect of the presence of Ru during plasma generation. Finally, the excited and ionized hydrogen atoms are confirmed as the primary accelerators in the plasma assisted CO2 methanation process. (C) 2017 Elsevier B.V. All rights reserved.