Plasma-Catalytic Dry Reforming of CH₄ over Calcium Oxide: Catalyst Structural and Textural Modifications

Abstract

The coupling of catalyst and nonthermal plasma for the dry reforming of methane was investigated with a special attention to the textural and structural catalyst modifications under plasma discharge. The reaction was performed using calcium oxide as material located into the DBD plasma reactor, while the deposited power was fixed at 8 W and the total gas flow at 40 mL/min (75% helium as diluent). The results obtained showed that CaO grain size affects the reactant transformation in the range: 250–1000 µm. CH₄ and CO₂ conversion increases from 18.1 to 21.1% and 8.7 to 11.2% respectively from the biggest to the smallest catalyst grain. Ethane formation is favored when the biggest particles are used, corresponding to the largest gas space between grains, suggesting the preferential recombination of CH₃ radicals to form C₂H₆ in gaseous phase and not at the surface of the solid. The reaction was performed from room temperature to 300 °C, little effect were observed for methane conversion while high CO₂ conversion was observed during the 20 min at 300 °C. The characterization of the catalyst after reaction under plasma shows structural catalyst modification and the carbonation of CaO at the highest temperatures. The amount of carbonate species was quantified and the results show that 59 monolayers of CaCO₃ are obtained after 1 h of plasma at P = 8 W using a mixture with a CH₄/CO₂ ratio of 2.