OXIDATIVE COUPLING OF METHANE .1. BEHAVIOR AND CHARACTERISTICS OF PB-MG-O CATALYSTS

The role of the lead active species has been studied for PbMgO catalysts in the oxidative coupling of methane. In general, the effect of adding lead to MgO was to increase the rate of total methane conversion. The C2 selectivity exhibited a volcano-type pattern with a maximum of 51% being achieved at about 0.4 at.% Pb. This volcano-type behavior is interpreted in terms of an "isolated site"-type mechanism. Addition of PbO in small amounts to a relatively inert MgO matrix results in the formation of a number of isolated strong oxidizing sites which can generate the methyl radicals more efficiently. Since these sites are isolated, the methyl radical has little likelihood of being further oxidized and can desorb into the gas phase where it can couple to form ethane. Surface and bulk characterization studies of the catalysts suggest that at low loadings the lead is indeed highly dispersed on the surface of the catalyst. © 1990.