Plasma-Catalysis of Non-Oxidative Methane Coupling: A Dynamic Investigation of Plasma and Surface Microkinetics over Ni(111)

A heterogeneous catalytic microkinetic model is developed and implemented in a zero4 dimensional plasma model for the dynamic study of methane non-oxidative coupling over Ni(111) at residence times and power densities consistent with experimental reactors.
The microkinetic model is thermodynamically consistent and is parameterised based on the heats of chemisorption of surface species on Ni(111). The surface network explicitly accounts for the interactions of plasma species, namely molecules, radicals and vibrationally excited states with the catalyst active sites via adsorption and Eley-Rideal reactions. The Fridman-Macheret model is used to describe the enhancement of the rate of the dissociative adsorption of vibrationally excited CH4, H2 and C2H6. In combination with a previously developed detailed kinetic scheme for non-thermal methane plasma, 0D simulation results bring insights on the complex dynamic interactions between
the plasma phase and the catalyst during methane non-oxidative coupling. Differential turnover frequencies achieved by plasma-catalysis are higher than those of equivalent plasma-only and catalysis-only simulations combined, however this performance can only be sustained momentarily. Hydrogen produced from dehydrogenation of ethane via electron collisions within the plasma is found to quickly saturate the surface and even promote the conversion of surface CH3∗ back to methane.