Reactivity of lanthanum substituted cobaltites toward carbon particles

This work reports on the reactivity toward carbon of a La0.5Sr0.5CoO3−δLa0.5Sr0.5CoO3−δ perovskite prepared by spray pyrolysis. It is shown that this perovskite presents a moderate activity for the thermal oxidation of carbon, producing a decrease in its temperature of combustion of ca. 150 °C and a significant increase in the selectivity toward CO2. Different experiments were carried out with electron energy loss spectroscopy (EELS) and X-ray photoemission spectroscopy (XPS) for the perovskite and its physical mixture with a high-surface area carbon material. In the physical mixture, the cobalt at the surface was partially reduced to Co2+ even at room temperature. XPS demonstrated a species of oxygen with low electron density at the catalyst surface. This species seemed to play a significant role in the oxidation processes at the perovskite surface. A model is proposed to account for the changes exhibited by the catalyst during its reaction with carbon.