Carbon dioxide conversion and characterization of microwave-induced plasma

Abstract

Microwave-induced non-thermal plasma technology is a promising solution to dissociate carbon dioxide, opening the possibility of carbon dioxide upgrade to value-added products and therefore providing an attractive approach in recent decarbonization endeavors. This study aims to comprehensively characterize and optimize microwave-induced pure carbon dioxide plasma focusing on the enhancement of conversion and energy efficiency. Analysis of optical emission spectra and gas composition under varying flow rates, introduced microwave power, and operating pressures was performed, while specific calculations were applied to support the measurement including electron concentration, electron temperature, and plasma gas temperature. A characteristic curve of carbon dioxide plasma is introduced as a novel outcome, which helps to elucidate the positive impact of applying reduced pressure. 46.4% carbon dioxide conversion efficiency was demonstrated by applying 5 NL·h⁻¹ flow rate, 80 mbar, and with 14.5 MJ·mol⁻¹ molar energy input utilizing only neat carbon dioxide, and achieved with continuous operation, without using any catalyst, in a straight waveguide system. The results indicate that lowering the pressure enhances the specific power absorption of plasma from the electromagnetic field through electron collisions, which increases the carbon dioxide conversion instead of converting it into heat.