We measured the conversion percentage of CO2 resulting from a single pass through the discharge region of the DBD plasma reactor. The conversion ratio of each catalyst is shown in Figure as a function of input power. The conversion percentage of CO2 increased significantly as a function of input power for each tested catalyst. The trend of increasing CO2 conversion rate with increasing input power, regardless of catalyst, has been observed in previous work, and is typically attributed to both an increase in the frequency of micro-discharges and an increase in the average electron energy in the discharge gap. However, we observed a diminishing relationship between CO2 conversion rate and input power of the reactor in all cases. The conversion ratio and input power conversion efficiency in the empty reactor, as shown in Figure , was consistently lower than the reactor filled loaded with the bare support material or any of the tested catalyst at all input powers. While it is not possible to exclude the heterogeneous effects of the quartz tube surface, we used the empty tube measurements as the baseline for the direct, uncatalyzed plasma reaction process. It is also not possible to isolate surface interactions from the mass transport effects of the bare support. The difference in reactivity between the empty reactor and the bare support while the surface composition is practically the same (significantly SiO2) does indicate that there are non-catalytic effects of making the pathway through the reactor more tortuous. This is likely due to the characteristics of the plasma-support interactions and to the increased residence time of the gas in the plasma volume.