Effect of O₂ on Plasma-Based Dry Reforming of Methane: Revealing the Optimal Gas Composition via Experiments and Modeling of an Atmospheric Pressure Glow Discharge

Abstract

Plasma technology is gaining increasing interest for the conversion of greenhouse gases, such as CO 2 and CH 4 , into value-added chemicals using (renewable) electricity. In this paper, we study the effect of O 2 addition to the combined conversion of CO 2 and CH 4 in an atmospheric pressure glow discharge plasma. This process is called "oxidative CO 2 reforming of methane", and we search for the optimal gas mixing ratio in terms of conversion, energy cost, product output and plasma stability. A mixing ratio of 42.5:42.5:15 CO 2 /CH 4 /O 2 yields the best performance, with a CO 2 and CH 4 conversion of 50 and 74%, respectively, and an energy cost as low as 2 eV molecule −1 (corresponding to 7.9 kJ L −1 and 190 kJ mol −1 ), i.e., clearly below the target defined to be competitive with other technologies. The syngas components (CO and H 2 ) are the most important products, with a syngas ratio, H 2 /CO, being 0.8. Plasma destabilization at high CH 4 fractions due to solid carbon formation is the limiting factor for further improving this syngas ratio. The solid carbon material is found to be contaminated with steel particles originating from the electrode material, rendering it unappealing as a side product. Therefore, O 2 addition helps to remove the carbon formation. Besides the experiments, we developed a 2D axisymmetric fluid dynamics model, which can successfully predict the experimental trends in conversion, product composition and temperatures, while providing unique insights in the formation of C x H y species.