Effects of composition and method of preparation of lead-containing oxide systems on their catalytic properties in the oxidative dimerization of methane

The effects of the Pb-Sn-O composition, the method of precipitating the active components, and modification with alkaline earth metals on the physico-chemical and catalytic properties of lead-tin catalysts in oxidative dimerization of methane have been studied. The effect of the phases of lead orthostannate, Pb₂SnO₄, on the surface properties of the Pb-Sn-O system has been established. The most selective composition has a ratio PbO : SnO₂ - 80 : 20 mole % on α-Al₂O₃ with divalent metal hydroxides. Introduction of alkaline earth metals into the Pb-Sn-O/α-Al₂O₃ system leads to stabilization of lead in its 4-valent state with formation of metal orthoplumbates, M₂PbO₄, and to a decrease in selectivity with respect to C₂-hydrocarbons. The increased catalytic activity of the modified M-Pb-Sn-O/α-Al₂O₃ samples (M = Ba, Sr, Ca, and Mg) is determined by the presence of tightly bound oxygen. Conclusions about the nature of the interaction of the reagents with the surface of the catalyst were reached.