Promoting effect of F− on Sr/La oxide catalysts for the oxidative coupling of methane Original Research Article

The catalytic performance evaluation results showed that the CH4 conversion, C2 selectivity and ethylene to ethane ratio were significantly higher over LaF3/SrO and SrF2/La2O3 than those over SrO/La2O3 and the maximum C2 yields of 18–20% were achieved over the LaF3/SrO and SrF2/La2O3 catalysts at 650–750°C. XRD analysis of the fresh catalysts indicated that, with the addition of LaF3 to SrO and treatment in air at high temperature, anionic and/or cationic exchange between oxides and fluorides lattices took place to some extent, leading to the formation of SrF2 and LaOF. The UV spectra of pyridine adsorption and the temperature-programmed desorption spectra of CO2 adsorption on SrF2/La2O3 and SrO/La2O3 showed that surface of the catalyst containing fluoride was more acidic and less basic than that of the corresponding oxide system. The XPS characterizations of O2-adsorbed catalysts revealed that the catalysts containing F− were more conducive to the formation of the oxygen species with fewer negative charges. The results of in situ IR characterization of the surface oxygen species at 650°C suggested that O2− might be the active oxygen adspecies for the oxidative coupling of methane reaction.