A- and B-Site Substituted Lanthanum Cobaltite Perovskite as High Temperature Oxygen Sorbent. 1. Thermogravimetric Analysis of Equilibrium and Kinetics

Perovskite samples of the general formula La 0.1 A 0.9 Co y Fe 1- y O 3- δ (where A = Ca, Sr, Ba; y = 0.1, 0.5, 0.9) were synthesized in our laboratory. Further substitution of Sr to a small extent by Ag and complete substitution of La by Sr were also studied. For a fixed perovskite composition (SrCo 0.5 Fe 0.5 O 3- δ ), samples obtained by carbonate coprecipitation and citrate methods of synthesis were compared. Use of helium as the carrier gas produced more weight loss (i.e., higher oxygen vacancy) than nitrogen in all the perovskite samples. Oxygen sorption equilibrium and sorption kinetics were thermogravimetrically studied in the temperature range 500−800 °C at atmospheric pressure using oxygen−nitrogen mixtures in which the oxygen fraction ranged from ∼5 to 50%. Desorption kinetics were studied by allowing the equilibrated sample to desorb in pure nitrogen. For a fixed B-site substitution, oxygen capacity varied with A-site substitution in the order Sr > Ba > Ca. Considering both equilibrium capacity and sorption−desorption kinetics, SrCo 0.5 Fe 0.5 O 3- δ and La 0.1 Sr 0.8 Ag 0.1 Co 0.5 Fe 0.9 O 3- δ were found to be the more promising candidates for further investigation.