Characterization of BaX₂/Gd₂O₃ (X=F, Cl, Br) catalysts for the oxidative coupling of methane

The reactivities of the BaX₂/Gd₂O₃ (X=F, Cl, Br) catalysts in the oxidative coupling of methane (OCM) reaction have been investigated. It has been observed that BaF₂, BaCl₂, or BaBr₂ can significantly improve the catalytic performance of Gd₂O₃. The X-ray diffraction (XRD) results indicated that ionic substitutions between the BaX₂ and Gd₂O₃ phases occurred during the preparation of the BaX₂/Gd₂O₃ catalysts as well as in the course of the OCM reaction. O₂-TPD, O₂-pulse, and Raman results showed that such ionic substitutions could lead to the increase in the amount of oxygen adsorbed on the BaX₂/Gd₂O₃ catalysts, resulting in the promotion of catalytic performance. Based on the results of XPS and halide content analyses, we realized that the halides in the BaX₂/Gd₂O₃ catalysts behaved rather differently in the OCM reaction. The catalytic performance of the BaX₂/Gd₂O₃ catalysts as related to reaction time can be correlated to the behaviours of the halides in the catalysts.