Dielectric Barrier Discharges in CO₂ and CH₄ at Sub-Atmospheric Pressures

The following investigation is a study of low-pressure, non-thermal plasma catalysis of greenhouse gases (GHGs), particularly CO₂ and CH₄, into high-value products. Non-thermal plasmas (NTPs), with mean energy of 1-10 eV, have potential to activate and dissociate ground-state gas molecules and allow reactions to occur at relatively low temperatures and atmospheric pressure. NTPs have shown to break the chemical bonds of the CO₂ and CH₄ molecules without the presence of a catalyst; however, the selectivity of desired products is poor due to unselective collisions between the active species. Dielectric Barrier Discharge (DBD) plasma of these gases at atmospheric pressures has been widely studied for the mitigation of waste; however, little to no literature is available on the behavior of these DBD plasmas at sub-atmospheric conditions. Preliminary data has shown that these processes at sub-atmospheric pressures are more efficient and require significantly less energy consumption to convert inert gases. Various designs of plasma reactors, which were based on DBD, have been designed to test their ability to operate efficiently low temperatures. All tested reactors had very low fabrication cost and simplicity in design. All prototype DBD reactors have been operated at pressures below 200 Torr. They have been investigated utilizing CO₂ and CH₄ gases at different flow rates and ratios of gas components. Plasma drivers used in this study included a nanosecond pulsed power source with square wave pulses up to 20 kV and operated at frequencies up to 10 kHz as well as a low frequency plasma driver for capacitive loads with voltages up to 40 kV at 300W power. The in-situ plasma species depending on pressure, frequency, and reactor configuration were analyzed using optical emission spectroscopy (OES). Downstream products were analyzed using Fourier transform infrared spectroscopy (FTIR) and gas chromatography (GC), equipped with flame ionization detection (FID), thermal conductivity detector (TCD), and mass spectrometer (MS).