Carbon dioxide conversion upon dilution by argon and nitrogen at atmospheric pressure has been studied using a barium titanate packed bed, non-thermal plasma reactor. The results show that the packed bed reactor with the BaTiO3 ferroelectric packing material directly contacting to electrodes provided a higher CO2 conversion and energy efficiency than a dielectric barrier discharge reactor with and without packed materials using electrodes covered by dielectric layers. In the packed bed reactor, the CO2 conversion increased from 19% in pure CO2 to 36% upon diluting the CO2 with 80% argon and to 35% with 80% nitrogen at a specific energy input (SIE) of 36 kJ L-1. The energy efficiency was approximately constant at ca. 0.24 mmol kJ(-1) for pure CO2 dissociation upon increasing SIE, but decreases upon dilution by Ar and is more pronounced by N-2. In addition to the major products of CO and O-2, up to 100 ppm of ozone was produced in a CO2/Ar plasma, but not in a CO2/N-2 plasma where some nitrogen oxides (N2O, NO and NO2), were observed with a total maximum concentration of 3120 ppm. Possible mechanisms are presented for the effect of Ar and N-2 on the dissociation of CO2 and for the formation of O-3, N2O and NOx based on discharge processes in the plasma and the subsequent chemistry. Electrical characterisation of the pure CO2, CO2/Ar and CO2/N-2 plasmas was also undertaken. The results suggest the formation of by-products can be controlled by varying the dilution gas fraction and operating conditions. (C) 2017 Elsevier B.V. All rights reserved.