Numerical study on the reaction mechanism of CO2 hydrogenation in atmospheric-pressure dielectric barrier discharge

Abstract

Recently, the catalytic conversion of greenhouse gases by plasma technology has attracted more and more attention. In this paper, a two-dimensional fluid model is developed to study the reaction mechanism of plasma CO2 hydrogenation in atmospheric-pressure dielectric barrier discharge (DBD). The effect of varying volume ratio of CO2/H2 on reaction mechanism of CO2 hydrogenation is studied carefully, such as temporal and spatial density distributions of main radicals and ions, dynamics of streamer propagation, and generation and loss pathways of H, CO, and CH3OH. It is found that H, O, and CO are the three most abundant species, and lower hydrogen content in gas mixture promotes streamer propagation and the formation of conduction current in plasma column. Besides, H is mainly produced by electron-impact dissociation of H2 (e + H2 ⇒ e + 2H); O and CO are dominantly produced by electron-impact dissociation of CO2 (e + CO2 ⇒ e + CO + O). Interestingly, H addition reaction to the intermediate species CH3O (CH3O + H ⇒ CH3OH) is found to be the main reaction pathway for methanol formation. Finally, a schematic overview of dominant reaction pathways for plasma CO2 hydrogenation in atmospheric DBD is presented, which ultimately leads to a better understanding of the intrinsic reaction mechanism.