Identifying the Role of A-Site Cations in Modulating Oxygen Capacity of Iron-Based Perovskite for Enhanced Chemical Looping Methane-to-Syngas Conversion

Suppressing coke deposition over reduced oxygen carriers, the key to breaking competing effects between oxygen supply and methane-to-syngas selectivity, is an important but challenging task for chemical looping partial oxidation technology. We report that A-site engineering of La1-xSrxFe0.8Al0.2O3 oxides significantly adjusts the oxygen capacity, which nearly triples from 1.0 mmol/g (x = 0.1) to 2.7 mmol/g (x = 0.5) with CO selectivity maintaining above 94%. Characterization results show that doping of Sr at the La-site induces dynamic crystal reconstruction from perovskite to Fe-0 and LanSrFen-xAlxO3n+1 (n = 1 and 2) oxides with Ruddlesden-Popper (RP) structure, possessing good methane activation and oxygen transport property, respectively. Spontaneously growth of RP oxides around Fe-0 rapidly delivers lattice oxygen from perovskite oxide to Fe-0. Density functional theory calculations further suggest that introduction of Sr notably reduces oxygen vacancy formation energy, leading to better oxygen donating ability. The synergy between dynamic structure evolution and oxygen mobility modulation greatly improves methane-to-syngas performance, which provides meaningful guidance to design advanced catalysts with better oxygen capacity for specific catalytic transformations.