Composite catalysts based on the CaO‒Fe₂O₃ system for the oxidative conversion of methane

The catalysts of the CaO‒Fe2O3 system with Fe2O3 content in the range of 0‒100 wt.% were synthesized by the solid state method at 900 and 1000 °C. The catalysts were characterized by XRD and SEM‒EDX methods, and their activity in the oxidative conversion of methane at 750 °C was studied. The phase composition of the catalysts corresponds to the CaO‒Ca2Fe2O5, Ca2Fe2O5‒CaFe2O4 and CaFe2O4‒a-Fe2O3 regions of the phase diagram. The specific catalytic activity dependence on the Fe2O3 content has an extremum. The CaO‒Ca2Fe2O5 catalysts have the highest reactivity and the active centers in them are localized at the phase interface. The activity of Ca2Fe2O5–CaFe2O4 samples decreases with an increase in the CaFe2O4 content. The CaFe2O4‒a-Fe2O3 catalysts have a core-shell structure and exhibit the least activity, which is determined by the CaFe2O4 shell.