Oxidative coupling of methane over Na⁺-ZrO₂-Cl^-/Al₂O₃ catalysts

Oxidative coupling of methane (OCM) was carried out over Na⁺-ZrO₂-Cl /Al₂O₃ catalysts in a temperature range from 1023 to 1123 K. The catalysts were prepared by impregnating the α- or γ-Al₂O₃ supports with sodium carbonate and/or zirconyl chloride. The OCM activity was examined using the catalysts prepared by three different preparation procedures. The best catalyst was the one prepared by subsequent impregnation of sodium carbonate-preimpregnated γ-Al₂O₃, with a mixed solution of sodium carbonate and zirconyl chloride. It was found that preimpregnated sodium played an important role in reducing the combustion activity of the γ-Al₂O₃. The catalyst with an optimal composition showed the highest C₂ selectivity and yield of 40.8% and 15.1 %, respectively. From the X-ray diffraction analysis it was found that tetragonal ZrO₂ was formed and that NaCl existed in the catalysts with relatively high sodium contents.