CO2 conversion in a dielectric barrier discharge plasma: N2 in the mix as a helping hand or problematic impurity?

Abstract

Carbon dioxide conversion and utilization has gained significant interest over the years. A novel gas conversion technique with great potential in this area is plasma technology. A lot of research has already been performed, but mostly on pure gases. In reality, N₂ will always be an important impurity in effluent gases. Therefore, we performed an extensive combined experimental and computational study on the effect of N₂ in the range of 1–98% on CO₂ splitting in dielectric barrier discharge (DBD) plasma. The presence of up to 50% N₂ in the mixture barely influences the effective (or overall) CO₂ conversion and energy efficiency, because the N₂ metastable molecules enhance the absolute CO₂ conversion, and this compensates for the lower CO₂ fraction in the mixture. Higher N₂ fractions, however, cause a drop in the CO₂ conversion and energy efficiency. Moreover, in the entire CO₂/N₂ mixing ratio, several harmful compounds, i.e., N₂O and NO_x compounds, are produced in the range of several 100 ppm. The reaction pathways for the formation of these compounds are explained based on a kinetic analysis, which allows proposing solutions on how to prevent the formation of these harmful compounds.