First-principles investigation of the coupling-induced dissociation of methane and its transformation to ethane and ethylene

Highlights: • Novel bimolecular coupling induced mechanism for CH bond dissociation of methane. • Direct formation of ethane and hydrogen radicals via a symmetric transition state. • High activation barrier due to severe repulsion and deformation of molecules. • Formation of ethylene and H₂ molecule via two symmetric sequential transition states. • Lower barrier for H₂ molecule assisted dehydrogenation of ethane. Quantum chemical computations predict that compression of the methane dimer to an inter-nuclear separation lower than 2 Å facilitates a concerted coupling and dissociation of CH bonds of the molecules to form ethane/ethylene. In this bimolecular, concerted mechanism, ethane formation is accompanied by production of H radicals from each methane moiety that may further abstract hydrogen atoms to lead to ethylene formation. Alternatively, transformation to ethane and ethylene proceeds via stepwise molecular hydrogen elimination, with the first eliminated hydrogen molecule originating from one of the methane moieties, accompanied by an intermolecular hydrogen transfer, and the second originating from both methyl groups.