A coaxial double dielectric barrier discharge (DBD) reactor is developed for plasma-catalytic conversion of CH4 and CO2 into syngas and other valuable products. A supported metal catalyst (Ni/Al 2O3) reduced in a methane discharge is fully packed into the discharge region. The influence of the Ni/Al2O3 catalyst packed into the gas gap on the electrical characteristics of the discharge is investigated. The introduction of the catalyst pellets leads to a transition in discharge behaviour from a typical filamentary microdischarge to a combination of spatially limited microdischarges and a predominant surface discharge on the catalyst surface. It is also found that the breakdown voltage of the CH4/CO2 discharge significantly decreases when the reduced catalyst is fully packed in the discharge area. Conductive Ni active sites dispersed on the catalyst surface contribute to the expansion of the discharge and enhancement of charge transfer. In addition, plasma-catalytic dry reforming of CH4 is carried out with the reduced Ni/Al 2O3 catalyst using a mixing ratio of CH 4/CO2 = 1 and a total flow rate of 50 ml min-1. An increase in H2 selectivity is observed compared with dry CH 4 reforming with no catalyst, while the H2/CO molar ratio significantly increases from 0.84 to 2.53 when the catalyst is present. © 2011 IOP Publishing Ltd.