CONSTITUENT SELECTION AND PERFORMANCE CHARACTERIZATION OF CATALYSTS FOR OXIDATIVE COUPLING OF METHANE AND OXIDATIVE DEHYDROGENATION OF ETHANE

The catalytic property of BaF2-doped tetragonal LaOF catalysts for oxi dative coupling of methane and oxidative dehydrogenation of ethane was evaluated in detail by independently varying the concentration of BaF 2 in the catalysts. The results indicate that addition of BaF2 into th e tetragonal LaOF significantly improves the catalytic performance of LaOF for both reactions, and the best results are observed over the Ba F2/LaOF catalysts with BaF2 content of ca. 10 mol%. The XRD analysis o f the fresh catalysts suggests that, for the catalysts with BaF2 conte nt less than 15 mol%, most of the Ba2+ ions together with the accompan ying F- and O2- may be dispersed in the LaOF, forming a Ba2+-doped LaO F phase in which some of the La3+ lattice points might be replaced by the less positively charged Ba2+, leading to the formation of an F-cen ter, anion vacancies or O- species in the LaOF lattice which will be f avorable to the adsorption and activation of O-2. The results of in si tu Raman characterization of the surface dioxygen species over the LaO F and 10% BaF2/LaOF catalysts suggest that the improvement of alkane c onversions on a BaF2-doped LaOF may be explained by the relative abund ance of the dioxygen adspecies over the catalyst. While one of the pos sible reasons for the significant improvement of the selectivities may have resulted from the favorable effect of F- ions for the isolation of the surface oxygen adspecies.