Activity of perovskite-type mixed oxides for the low-temperature CO oxidation: Evidence of oxygen species participation from the solid
Résumé
Oxygen mobility in LaFe1−x−yCuxPdyO3−δ is evaluated using oxygen isotopic exchange and equilibration techniques. Reducibility and oxygen desorption are strongly altered by the properties of the substituting cation, even if iron remains hardly reducible up to 1000 °C. In addition, large differences in oxygen mobility are measured by oxygen isotopic exchange. Large higher oxygen mobility is achieved over the Cu-containing sample, while Pd substitution inhibits oxygen mobility. These observations correlate well with the evolution of catalytic activity for low-temperature CO oxidation. Indeed, Cu-containing materials present the highest catalytic activities, while Pd-substituted structure shows a low-temperature activity similar as the Fe parent material. CO oxidation is usually considered as a suprafacial reaction, where only adsorbed gas-phase species are involved. Nevertheless, the participation of oxygen surface species to the reaction (in pure ferrite structure), or from the bulk (in Cu-substituted material), is strongly suggested by oxygen mobility measurement, suggesting a redox-type oxidation mechanism.