The effect of alkali promoters in oxidative coupling of methane with Mn-oxide catalysts

The catalytic oxidalive coupling of metnane to ethylene and ethane with manganese oxide catalysts promoted with alkali metal and alkali metallic-chloride has been studied at atmospheric pressure in a fixed bed flow reactor. The main studies of reaction were carried out over maganese oxide catalysts promoted with sodium chloride and the structure and surface morphology of these catalysts was characterized by an X-ray diffraction and a scanning electron microscope. The powdered MnO₂ was changed into Mn₂O₃, and MnO₂ containing alkali metallic-chlorides was not changed to new ternary oxides but changed into Mn₃O₄ and/or Mn₂O₃ at higher calcination temperature(above 780°C). The optimum content of NaCl promoted was 10–20wt%, an in over 10wt%, the conversion and the selectivity were kept constant. The main factor on deactivation of catalysts was the loss of thepromoter(NaCl). The addition of alkali metal salts to manganese oxide catalyst has enhanced C₂(C₂H₄ + C₂H₆) selectivity due to neutralizing acid sites more than the electronic factor. It was confirmed that chlorine in alkali metallicchloride has enhanced the formation of C₂H₄, resulting in a good C₂-yield (up to 25.7%).