Intermittent temperature-programmed desorption study of perovskites used for catalytic purposes
Résumé
A differential desorption technique, called intermittent temperature-programmed desorption (ITPD), was used to give new insights into the properties of La1−xSrxCo0.8Fe0.2O3 perovskites as a contribution to improve their performances with respect to various important application fields such as catalysis, electrocatalysis and solid oxide fuel cells (SOFC). Both ITPD and interrupted TPD (carried out at different heating rates) evidenced two distinct oxygen adsorbed states, desorbing at temperatures lower than 400 °C, corresponding to less than 5% of a compact monolayer of oxide ions. The first one, for low desorption temperatures (lower than 290 °C) exhibits a heat of adsorption (ΔH) distribution from 101 to 121 kJ mol−1. The second one, for higher desorption temperatures (between 290 and 400 °C) corresponds to ΔH = 146 ± 4 kJ mol−1. Additionally, for temperatures higher than 400 °C, we observed a continuous desorption of oxygen species, probably originating from the sub-surface or semi-bulk, with an associated activation energy of desorption ≥175 kJ mol−1.