Chemical looping combustion characteristics and kinetic behaviour of Sr‐doped perovskite‐type CaFeO₃ oxygen carriers: Theoretical and experimental investigations

Abstract

Oxygen carriers (OCs) with typical perovskite structures have attracted attention for use in chemical looping combustion (CLC) owing to their unique tunable structures and excellent performance. Thus, a further improvement in the reactivity and a deep understanding of the kinetic behaviour in CLC are highly desirable for such perovskite OCs. In this study, a series of Sr-doped perovskite-structured CaFeO 3 OCs (denoted as Sr x Ca 1Àx FeO 3 ) were synthesized. The CLC characteristics, kinetic behaviour, and doping mechanism were systematically investigated via experiments and density functional theory (DFT) calculations. The activation energies of Sr x Ca 1Àx FeO 3 OCs with various Sr contents were found to be in the range of 36.6-40.1 kJ/mol and lower than that of CaFeO 3 (62.7 kJ/mol), indicating that the Sr doping enhanced the reactivity of CaFeO 3 . Among the OCs, Sr 0.4 Ca 0.6 FeO 3 , which had the lowest activation energy and the fastest release of lattice oxygen, was regarded as the optimum OC. DFT calculations indicated that the reaction energy barrier of Sr x Ca 1Àx FeO 3 (0.73-1.06 eV) was lower than that of CaFeO 3 (2.18 eV). This suggests that Sr doping and the regulation of the reaction pathways are essential drivers for enhancing the reactivity of Sr x Ca 1Àx FeO 3 , which affects the release of lattice oxygen and the morphological properties of OC particles.