The carbon dioxide reforming of methane was performed with a cordierite honeycomb monolith packed-bed and dielectric barrier discharges. The reactor performance (reactant conversions and product selectivities) was evaluated with and without a nickel catalyst and by comparing two different power supplies, a pulsed excitation (fast-rising voltage) and a sinusoidal excitation. The chemical reactivity of the plasma discharges generated by the pulsed power supply was higher than that by the sinusoidal power supply. A positive effect on the chemical reactivity, ascribed to the promotion of reactant activation (dissociative adsorption) on the nickel particles, was observed in the case of sinusoidal-excitation-nickel-catalyst association.