Oxidative dimerization of methane over lead-magnesium mixed oxide catalysts

Abstract

While both methane combustion and methane ammoxidation to HCN over metal catalysts are well known, selective dimerization of methane in the presence of oxygen over oxide catalysts has been achieved only recently. We report results of the oxidative coupling of methane to form ethane and ethylene over a mixed PbO-MgO catalyst. Selectivity for methane conversion to higher hydrocarbons rises to over 80% as reactor temperature is raised to about 800°C over these catalysts when oxygen/methane in the feed is limited. However, selectivity declines as oxygen partial pressure is increased. Both observations are consistent with recently published results for other catalysts containing PbO. Here, optimal reaction conditions give yields of nearly 20%. The PbO-MgO catalyst operates effectively both with and without co-fed oxygen. Productivity, an important consideration for practical processes, was found to be about forty times higher when oxygen is co-fed. The rate of oxygen disappearance over PbO-MgO had a 2 3 order dependence on oxygen pressure under conditions where selectivity was high, indicating that oxygen activation has an important role in the coupling mechanism.