The Effect of Oxygen-Anion Conductivity of Metal–Oxide Doped Lanthanum Oxide Catalysts on Hydrocarbon Selectivity in the Oxidative Coupling of Methane
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文摘
La2O3was 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°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 O2−O22−) 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.