Development of a microkinetic model for non-oxidative coupling of methane over a Cu catalyst in a non-thermal plasma reactor

A surface microkinetic plasma model for non-oxidative coupling of methane into H2 and higher hydrocarbons was developed over a Cu catalytic film. Twenty key plasma species including electron, ions, radicals, and neutrals were considered in respective chemical reactions leading to the formation of C2 hydrocarbons onto the catalyst surface. The kinetic model was coupled with a global plasma model to describe the performance of a non-thermal plasma reactor. In the reactor model, the reactant gas flows between the two coaxial cylindrical metal electrodes with a length of 50 mm and a diameter of 2 mm (inner) and 6 mm (outer electrode) coated with a Cu film. The effect of discharge power, initial CH4 concentration, and inlet flow rate on methane conversion was investigated. The surface model shows that the CH4 conversion of 47% is obtained at a discharge power of 70 W with a selectivity of C2H2 (49%). Increase in power increased the conversion of methane while increase in pressure and/or inlet gas flow rate decreased it. Also, the results of the plasma-catalyst model were compared with those of plasma alone (without catalyst). It showed that presence of the catalyst inside the plasma increases the selectivity and yield of acetylene, while it deceases the selectivity and yield of hydrogen. Also, the density of radical CH3 in the plasma phase increased in the presence of catalyst, while CH2 and CH densities decreased with that.