THE EFFECTS OF TRANSITION-METAL OXIDES ON THE METHANE OXIDATIVE COUPLING ACTIVITY OF DOPED MGO CATALYSTS .1. ZINC AND MANGANESE

Magnesium oxide samples doped with different loadings of zinc and manganese oxides with and without lithium carbonate being present in the preparation were evaluated for their catalytic activity towards the oxidative coupling of methane to higher hydrocarbons. When Li2CO3 is excluded, the exhaustive reactions of methane to form carbon oxides are favoured. With a doped Li2CO3/MgO catalyst, a methane conversion of >25% and a selectivity to C, hydrocarbons of near 60% was retained but not enhanced in the presence of different loadings of Zn oxide at 805°C. Low loading of Mn oxide on Li2CO3/Mg0 resulted in a methane conversion of >35% and a selectivity to C2 hydrocarbons of near 50%. At high Mn oxide loadings the methane conversion decreases and the C2 selectivity is less than 30% due to more exhaustive oxidation. The activity of the doped catalyst is related to the physico-chemical properties, especially surface morphology, and metal oxide reducibility on the basis of SEM, XRD, TRP, and electron microprobe analysis. © 1991.