Promoter effects of dichloromethane on the oxidative coupling of methane over MnMgO catalysts Original Research Article

Small amounts of manganese oxide incorporated on MgO enhanced C2+ hydrocarbon selectivity during the oxidative coupling of methane (OCM). Both C2+ selectivity and CH4 conversion were also improved by adding alkaline metal halides. Dosing CH2Cl2 pulses into the CH/4O2 feed stream over alkali promoted Mnsingle bondMgO catalysts led to an improvement in the yield to C2+ hydrocarbons. The extent of this effect and the stability of the alkali phases were found to depend on the type of promoter. Photoelectron spectroscopy (XPS) revealed that all the used catalysts retained important amounts of chlorine in the form of Cl− ions, and simultaneously manganese was oxidized to Mn4+. In the light of quantitative XPS data, a redox mechanism consisting of the decomposition of halocompound at catalyst surface through formation of an oxyhalide of the type MnO2−x2Cl/x has been proposed. The different patterns for CH4 conversion and C2+ selectivity indicate a key role of the alkali promoter and its distribution on the surface, on the formation of this Cl-containing species.