The predominance of the Fe 4+ /Fe 3+ ratio over the oxygen vacancy concentration as the determining factor of the catalytic activity was also pointed out by Barbero et al . in their investigation of the catalytic performance of LaFeO3 perovskites doped with varying amounts of Ca for ethanol oxidation. It is noteworthy, however, that these authors reported an inverse order of influence for both aspects (number of vacancies > Fe 4+ /Fe 3+ ratio) in the case of the oxidation of another type of molecule, such as propane.