Plasma assisted non-oxidative methane coupling over Ni-Fe mixed metal oxides

In this work, Ni-Fe mixed metal oxides with different Fe/Ni molar ratios of 0.33, 1 and 3 were synthesized by hydrothermal method at a constant pH. The obtained catalysts were characterized via XRD, TEM, ICP-OES, XPS and nitrogen physisorption. The catalysts were tested at room temperature for plasma-assisted non-oxidative coupling of methane with a mixture of 20 vol% CH₄ in Ar in a planar DBD reactor with an electrode gap of 1.5 mm. The Fe₃Ni showed the highest methane conversion of 7.4% with a 26% selectivity towards ethylene and an energy consumption as low as 0.55 MJ·mol_C2H4^-1. The XPS spectra of Fe₃Ni showed a surface enrichment in Ni³⁺ and Fe²⁺ promoting ethylene desorption rate as compared with the other two synthesized catalysts. The CH₄ conversion increases up to 5 times with decreasing the CH₄/Ar molar ratio in the feed at constant flow rate of 100 ml∙min^-1. All the catalysts showed a similar relative decrease of conversion and increase of energy consumption. Negligible carbon deposition rate was observed and the total selectivity to C₂ and C₃ hydrocarbons was close to 100%, indicating the advantages of the catalytic formulation proposed for methane activation in plasma environment.