XANES study of Li-MgO and Li-La2O3-MgO catalysts for oxidative coupling ofmethane

To characterize the defect sites in the near-surface and bulk phase of Li-M gO and Li-La2O3-MgO, XANES at Mg K-edge and La L-3-edge was applied. For Li -MgO, it can be suggested that Li doping at a low content (2.5 wt%) brings about the formation of defect species only in the near-surface. This is due to the localization of doped Li ions in the surface, and thus the catalyti cally active species containing [Li+-O-] type center exist in the surface r egion. After OCM reaction, the defect species are formed in the near-surfac e over MgO and Li-MgO. By addition of La2O3 to Li-MgO (La/(Mg+La)=0.25), th e structural change during the reaction is almost suppressed in the surface . In addition, the Li-La2O3-MgO shows higher C-2 selectivity than Li-MgO.