The effect of oxygen-anion conductivity of metal-oxide doped lanthanum oxide catalysts on hydrocarbon selectivity in the oxidative coupling of methane

La2O3 was doped with cations of valencies different to La3+ (Sr2+, Zn2+, Ti4+, Nb5+) to alter the concentration of oxygen-anion vacancies in the host lattice and, hence, oxygen-anion conductivity. The conductivity and catalytic properties of these solids were determined between 700 and 850 degrees C. An increase in oxygen-anion conductivity improved C2+ selectivity. A high concentration of anion vacancies in the catalytic material favours the adsorption of gaseous oxygen and its immediate transformation into lattice oxygen; therefrom it is suggested, that the relative amount of weakly adsorbed electrophilic oxygen species (possibly O-2(-), O-2(2-)) is diminished in favour of more strongly bounded, nucleophilic species (O2-). Thereby, nonselective surface reactions of methyl radicals and/or C2+ hydrocarbons with electrophilic oxygen are suppressed. (C) 1997 Academic Press.