Oxidative coupling of methane over alkali chloride–Mn–Na2WO4/SiO2 catalysts: Promoting effect of molten alkali chloride

• Performance of alkali chloride–Mn–Na2WO4/SiO2 catalysts was investigated.
• Ethylene yield of 31% was obtained.
• Oxidative coupling of methane was promoted by molten alkali chloride species.

We investigated the effect of alkali chloride (MCl = LiCl, NaCl, KCl, CsCl, and equimolar mixture of NaCl and KCl) on catalytic performance of MCl–Mn–Na2WO4/SiO2 catalysts for oxidative coupling of methane. The MCl–Mn–Na2WO4/SiO2 catalysts exhibited higher methane conversion and ethylene selectivity than the catalyst without MCl, with the highest ethylene yield (31%) obtained with the NaCl-promoted catalyst at a reaction temperature of 1023 K. However, catalyst deactivation occurred because of the evaporation of MCl from the catalysts. Activity tests and high-temperature X-ray diffraction showed that molten MCl species promote the oxidative coupling reaction. Thus, the vapor pressure and melting point of MCl have a significant influence on the catalytic activity of the MCl–Mn–Na2WO4/SiO2 catalysts.