Conversion of CO2 in a packed-bed dielectric barrier discharge reactor

The conversion of CO2 into CO and O2 in a quartz cylindrical packed-bed dielectric reactor has been studied using CO2 and Ar gas mixtures at atmospheric pressure and near ambient temperature with quartz wool, γ-Al2O3, and TiO2 packing. The highest energy efficiencies and conversion rates were observed with TiO2 packing in 20% CO2 in Ar: 30% conversion with 2.9% energy efficiency, and 17.5% conversion with 5.0% energy efficiency. Both γ-Al2O3 and quartz wool also showed an enhancement in conversion over an unpacked reactor. The percentage of CO2 to Ar in the range of 20%–60% is shown to have only a minor effect on reactor performance. Conversion as a function of power input and flow rate is studied in detail for γ-Al2O3 and TiO2 packing with similar particle sizes. In both cases, simple chemical kinetic models show that the CO production rate is nearly equal for both materials, while reverse reaction rates to CO2 are doubled for γ-Al2O3 compared to TiO2. From detailed charge–voltage (Q-V) analysis of all four reactor configurations, it is revealed that the electric field at which discharging occurs is higher for both γ-Al2O3 and TiO2 as compared to the empty or quartz wool filled reactors. Comparing kinetic model results with the electrical Q-V analysis, it appears likely that the higher and similar magnitude electric fields occurring with γ-Al2O3 and TiO2 are directly responsible for the increased CO production rates via increased electron energies in the discharge. The higher reverse reaction rates for γ-Al2O3, and its subsequent poorer performance compared to TiO2, can be attributed to a significantly higher effective surface area, which increases undesirable surface reactions between CO and oxygen species.