Effect of Waveforms of Applied Voltage on CO2 Reforming of CH4 in an Atmospheric Plasma Reaction

CO₂ reforming of CH₄ to syngas has been the subject of great interest because two greenhouse gases are consumed and several valuable products can be produced. The products, such as ammonia, methanol, acetic acid, dimethyl ether, synthetic gasoline, and so on, can be used as the basic materials for other chemical reactions. Recently and traditionally, a catalytic method, a plasma method and a combined catalytic and plasma method have been employed for the reaction of  CO₂ reforming of CH₄.

Reaction with a catalyst is still considered an attractive method. However, the high temperature operation required for this method increases its cost. Also, the continuous formation and deposition of carbon black on the catalyst surface leads to the deactivation of the catalyst, which is the main disadvantage of this method. As an effective approach, a plasma method was suggested as a dry method of reforming methane without the concern about the formation of carbon black. Several plasma systems have been employed for CO₂ reforming of CH₄, such as thermal plasma, corona discharge, arc discharge and dielectric barrier discharge (DBD). Among the plasma systems, reaction by DBD has produced a relatively low degree of conversion of feed gases and selectivity of products. Therefore, many research groups have researched ways to improve the efficiency of reaction by DBD. Several research groups presented that CO₂-CH₄ reforming could be improved by a pulse type power supply. It was reported that the reaction by a DBD reactor was enhanced using a pulsed plasma, while the pulse width was not effective to enhance the conversion of reactants.

In this study, CO₂ reforming of CH₄ to syngas was performed by an atmospheric dielectric barrier discharge reactor immersed in an electrically insulating oil bath. For comparison of the effects of applied voltage waveforms on the reaction, two kinds of waveforms, namely, sinusoidal and pulse, were supplied to the plasma reactor for CO₂ reforming of CH₄. Several parameters such as reaction time and applied voltage were evaluated for the conversion of reactants, the selectivity of products, and energy efficiency for both waveforms of applied voltage.