Effect of CH4 dissociation products on the vibrational excitation of CO2 and CO in CO2-CH4 plasmas

The conversion of methane and carbon dioxide into value-added products (Dry Reformation of Methane) by plasma is a promising way to reach carbon-neutral and efficient energy storage.

 However, CO2/CH4 plasmas remain poorly known despite decades of studies on CO2 plasmas. The goal of this work is to provide a description of the vibrational excitation and quenching of CO2 and CO in CO2/CH4 plasmas in order to develop kinetic models.

To this aim, a glow discharge is ignited during 5ms in flowing conditions at low pressure (1 to 5 Torr) in a dedicated pyrex reactor.

The vibrational excitation of CO and CO2 is monitored in situ, during and after the pulse, with an FTIR spectrometer in “step-scan mode”.  The temperatures are obtained by fitting infrared spectra. The flows are varied to change the proportion of the gas renewed between pulses.

H, H2 and H2O are found to limit vibrational excitation of CO2 and are excellent quenchers while CO vibrations seem to benefit from the addition of CH4 in the initial mixture. Nevertheless, CO is also quenched efficiently by CH4 dissociation products. Quenching rates of vibrationally excited CO2 by other molecules are measured and compared with existing values.