CO2 conversion in a non-thermal, barium titanate packed bed plasma reactor: The effect of dilution by Ar and N2

Abstract

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 36kJL−1. The energy efficiency was approximately constant at ca. 0.24mmolkJ−1 for pure CO2 dissociation upon increasing SIE, but decreases upon dilution by Ar and is more pronounced by N2. In addition to the major products of CO and O2, up to 100ppm of ozone was produced in a CO2/Ar plasma, but not in a CO2/N2 plasma where some nitrogen oxides (N2O, NO and NO2), were observed with a total maximum concentration of 3120ppm. Possible mechanisms are presented for the effect of Ar and N2 on the dissociation of CO2 and for the formation of O3, N2O and NOx based on discharge processes in the plasma and the subsequent chemistry. Electrical characterisation of the pure CO2, CO2/Ar and CO2/N2 plasmas was also undertaken. The results suggest the formation of by-products can be controlled by varying the dilution gas fraction and operating conditions.