Partial reduction and re-oxidation of iron-and cobalt-containing perovskites using catalyst characterisation measurements

The oxygen uptake and release of La1−xSrxCo1−yFeyO3−δ (x=0.2, 0.4; y=0, 0.8, 1) perovskite powders was examined with temperature-programmed techniques. In addition to the commonly used temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO) was used to examine oxygen adsorption on the perovskites that had previously been partially reduced. While perovskite reduction started slowly at an offset temperature of about 300 °C, the re-oxidation already started below 100 °C resulting in a distinct re-oxidation peak. The measured oxygen stoichiometry changes were in the range of δ=0.03–0.19. For the re-oxidation process, surface-controlled kinetics was assumed, allowing the application of conventional temperature-programmed desorption (TPD) procedures to determine the activation energy of the adsorption process. Simulation of the peak profiles confirmed the predominant surface kinetics. The determined activation energies were in the range of 0.46–0.63 eV. For the measurements presented here, the demands made on preparation and experimental equipment are much lower than for other surface exchange characterisation techniques and allow a pre-selection of interesting perovskite materials for use in solid oxide fuel cells or as exhaust catalysts.