Study of glow and RF discharges in CO2/H2 mixtures*

CO2/H2 plasmas are promising for methanation process. However, full hydrogenation into CH4 cannot be achieved in a pure CO2/H2 mixture without catalysts, which complicates drastically the chemistry induced in such systems. As a first step, this study focusses on fundamental mechanisms of plasma and chemical kinetics taking place in pure CO2/H2 mixtures. To this end two complementary experiments were carried out: the study of a continuous glow discharge in flowing conditions and a RF pulsed plasma in a closed reactor. The glow discharge is homogeneous and allows measuring electric field, temperatures and species densities, making it suitable as benchmark for 0D kinetic model (LoKi-C in our case).  The second experiment enables to assess the chemical kinetics in consecutive RF plasma pulses ignited while the densities of IR-reactive molecules are monitored in time by infrared absorption, until all molecular densities reach their steady-state values [1]. The influence of processes with different characteristic times is investigated by varying the plasma pulse duration and frequency. The influence of surface processes in the chemical kinetics of this discharge is evinced, in particular the role of water adsorption on the reactor walls.

[1] Morillo Candas et al, J. Phys. Chem. C 2020, 124, 32, 17459–17475