As can be seen, BaFeO2.90 exhibits better performance over the whole temperature range tested, achieving significantly higher conversion values than BaFeO2.78 even at low temperatures. The superior behavior of BaFeO2.90 is also evident from the values obtained for the light-off temperature which is almost 120 ºC lower for BaFeO2.90 (320 and 440 ºC for BaFeO2.90 and BaFeO2.78, respectively). According to the previous characterization of the samples, the above results suggest a clear influence of the oxidation state of iron on the CO conversion capacity of the perovskite, which increases as the Fe 4+ content increases or, in other words, with the Fe oxidation degree. ratio would be the key parameter to explain the catalytic activities shown by the BaFeO3δ oxides here investigated. Accordingly, we may propose a mechanism for CO oxidation on these materials based on a redox cycle, in which iron is initially reduced, by providing the necessary oxygen for CO oxidation, and subsequently undergoes re-oxidation through interaction with gaseous oxygen. This mechanism is allowed by the remarkable reversibility of the anionic lattice to release and incorporate oxygen over a very large compositional range (0 <  < 0.40) while keeping the main structural features of the 6Hpolytype.