LI-DOPED MGO AS CATALYSTS FOR OXIDATIVE COUPLING OF METHANE - A POSITRON-ANNIHILATION STUDY

Magnesium oxides intentionally doped with lithium (with a maximum Li content of 40 mol%) for use as catalysts for oxidative coupling of methane were characterized by means of positron annihilation. The positron lifetime spectra, which could be reasonably well interpreted within the framework of the well-known trapping model, depend on the amount of Li doping of the MgO suggesting that positrons are trapped at dispersed small Li2CO3 precipitates. Very similar dependencies on lithium doping of the C2 selectivity and the positron trapping rate-kappa imply an intimate relationship between the concentration of [Li]0-centers (also referred to as [Li+O-] centers) and the selective activity of Li/MgO during catalytic reactions.