Kinetic and Thermodynamic Enhancement of Low-Temperature Oxygen Release from Strontium Ferrite Perovskites Modified with Ag and CeO(2)

[Image: see text] The redox behavior of the nonstoichiometric perovskite oxide SrFeO(3−δ) modified with Ag, CeO(2), and Ce was assessed for chemical looping air separation (CLAS) via thermogravimetric analysis and by cyclic release and uptake of O(2) in a packed bed reactor. The results demonstrated that the addition of ∼15 wt % Ag at the surface of SrFeO(3−δ) lowers the temperature of oxygen release in N(2) by ∼60 °C (i.e., from 370 °C for bare SrFeO(3−δ) to 310 °C) and more than triples the amount of oxygen released per CLAS cycle at 500 °C. Impregnation of SrFeO(3−δ) with Ag increased the concentration of oxygen vacancies at equilibrium, lowering (3 – δ) under all investigated oxygen partial pressures. The addition of CeO(2) at the surface or into the bulk of SrFeO(3−δ) resulted in more modest changes, with a decrease in temperature for O(2) release of 20–25 °C as compared to SrFeO(3−δ) and a moderate increase in oxygen yield per reduction cycle. The apparent kinetic parameters for reduction of SrFeO(3−δ), with Ag and CeO(2) additives, were determined from the CLAS experiments in a packed bed reactor, giving activation energies and pre-exponential factors of E(a,reduction) = 66.3 kJ mol(–1) and A(reduction) = 152 mol s(–1) m(–3) Pa(–1) for SrFeO(3−δ) impregnated with 10.7 wt % CeO(2), 75.7 kJ mol(–1) and 623 mol(O(2)) s(–1) m (–3) Pa(–1) for SrFeO(3−δ) mixed with 2.5 wt % CeO(2) in the bulk, 29.9 kJ mol(–1) and 0.88 mol(O(2)) s(–1) m(–3) Pa(–1) for Sr(0.95)Ce(0.05)FeO(3−δ), and 69.0 kJ mol(–1) and 278 mol(O(2)) s(–1) m(–3) Pa(–1) for SrFeO(3−δ) impregnated with 12.7 wt % Ag, respectively. Kinetics for reoxidation were much faster and were assessed for two materials with the slowest oxygen uptake, SrFeO(3−δ), giving the activation energy E(a,oxidation) = 177.1 kJ mol(–1) and pre-exponential factor A(oxidation) = 3.40 × 10(10) mol(O(2)) s(–1) m(–3) Pa(–1), and Sr(0.95)Ce(0.05)FeO(3−δ), giving the activation energy E(a,oxidation) = 64.0 kJ mol(–1), and pre-exponential factor A(oxidation) = 584 mol(O(2)) s(–1) m(–3) Pa(–1).