Alkali metal-doped transition metal oxides active for oxidative coupling of methane

Addition of alkali metals to the oxides of transition elements endowed the oxides with the ability for converting methane into C2 compounds (C2H6 + C2H4). Among the combinations of alkali metals and transition metal oxides tested, the lithium added nickel oxide was the most active catalyst for the reaction. X-ray diffraction (XRD) analysis showed that the catalyst was a solid solution of lithium in NiO. The reaction of methane with the lattice oxygen atoms of the stoichiometric solid solution, LiNiO2, produced C2 compounds very selectively. The XRD analysis of the sample showed that the reaction proceeded as 2LiNiO2 + 2CH4 → Li2O + 2NiO + C2H6 + H2O. Oxidation of the reduced catalyst by oxygen regenerated LiNiO2 as Li2O + 2NiO + 1/2O2 → 2LiNiO2. Thus, it is concluded that the oxidative coupling of methane proceeds via the redox mechanism of LiNiO2. The stability of the solid solution of alkali metals with transition metal oxides under steady state reaction conditions is essential for the alkali-doped oxides to be effective in the oxidative coupling of methane.