EFFECT OF SULFUR ON THE OXIDATIVE COUPLING OF METHANE OVER A LANTHANA CATALYST

Addition of trace amounts of H2S to the reactants for methane oxidative coupling results in the formation of SO(x) and poisoning of a lanthanum oxide catalyst. Poisoning has little effect on C2+ selectivity until conversion fall to a low level. The factors controlling catalyst poisoning were found to be sulfur concentration, gas flow-rate and catalyst temperature. Poisoned catalyst was characterised by FT-IRS,XRD, O-18(2) exchange capacity and TGA, and was found to involve formation of inactive La2O2SO4 which has a decomposition temperature of ca. 900-degrees-C under reaction conditions. An equilibrium is set up between formation and decomposition of the La2O2SO4, and the extent of poisoning depends on partial pressure of SO2.