AVS 61st International Symposium & Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS+SE-ThA

Paper PS+SE-ThA6
In Situ Diagnostic Studies of CO2 containing Dielectric Barrier Discharges

Thursday, November 13, 2014, 4:00 pm, Room 308

Session: Atmospheric Pressure Plasma Processing; Fundamental and Applications
Presenter: Stefan Welzel, FOM Institute DIFFER; Eindhoven University of Technology, Netherlands
Authors: S. Welzel, FOM Institute DIFFER; Eindhoven University of Technology, Netherlands
F. Brehmer, Eindhoven University of Technology; AFS GmbH, Germany
B.L.M. Klarenaar, Eindhoven University of Technology, Netherlands
M.C.M. van de Sanden, FOM Institute DIFFER; Eindhoven University of Technology, Netherlands
R. Engeln, Eindhoven University of Technology, Netherlands
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Carbon dioxide will be a key enabler for the integration of renewable energy into a future CO2 neutral energy system as well as into chemical industry. The application of non-equilibrium plasmas offers a promising route to overcome the initial energy-demanding CO2 dissociation step. Through subsequent hydrogenation of the CO produced, gaseous or liquid hydrocarbon(ate)s are synthesised. Dielectric barrier discharges (DBDs) are known as useful tools in plasma-assisted gas conversion. The main objective was to unravel main reaction mechanisms in CO2 containing DBDs through combination of several in-situ diagnostic techniques.

Optical emission spectroscopy, (infrared) absorption spectroscopy along with rotational Raman scattering were employed to study the CO2 conversion and deduce gas temperatures in mid-frequency (kHz) driven DBDs at elevated pressures. To study the kinetics of CO formation the DBD was additionally operated in pulsed mode. Absolute densities of CO, O2 and O3 were established downstream the plasma reactor. The CO yield was typically below 5% for gas flow rates that would allow reasonable throughput. The generally weak emission of electronically excited species (CO2+, CO) was monitored during individual AC cycles. Additionally, phase- and time-resolved signals of ro-vibrational absorption lines of CO and CO2 in their (electronic) ground state were detected by quantum cascade laser absorption spectroscopy. In contrast to emission, the CO absorption remained constant throughout individual AC cycles. The modulation of CO absorption signals during pulsed operation can be successfully modelled by considering the power density of the DBD, the reactor wall and gas temperatures (up to 550 K), and the residence time of the gas along with the reactor geometry.

The results suggest electron-impact CO2 excitation and ionisation followed by potentially surface enhanced recombination. The stoichiometric CO:O2 ratio is described by a uniform trend as function of the number of charges transferred during the residence time of CO2 in the active plasma zone.