Avoiding solid carbon deposition in plasma-based dry reforming of methane

Solid carbon deposition is a persistent challenge in dry reforming of methane (DRM), affecting both classical and plasma-based processes. In this work, we use a microwave plasma in reverse vortex flow configuration to overcome this issue in CO2/CH4 plasmas. Indeed, this configuration efficiently mitigates carbon deposition, enabling operation even with pure CH4 feed gas, in contrast to other configurations. At the same time, high reactor performance is achieved, with CO2 and CH4 conversions reaching 33% and 44% respectively, at an energy cost of 14 kJ L-1 for a CO2 : CH4 ratio of 1 : 1. Laser scattering and optical emission imaging demonstrate that the shorter residence time in reverse vortex flow lowers the gas temperature in the discharge, facilitating a shift from full to partial CH4 pyrolysis. This underscores the pivotal role of flow configuration in directing process selectivity, a crucial factor in complex chemistries like CO2/CH4 mixtures and very important for industrial applications.Our work demonstrates that solid carbon-free conversion of green-house gases into value-added compounds is possible by changing the gas flow configuration in a microwave plasma, making significant strides in green chemistry.