Mechanism of lattice oxygen migration in decarburized Fe-based oxygen carriers to chemical looping gasification

Abstract

In chemical looping cycling, Fe-based oxygen carriers often suffer from agglomeration and phase separation. This study addresses these issues by developing a decarbonized Fe-based oxygen carrier with NiFe₂O₄ as the active site, CaO as the decarbonizer, and La₂O₃ as the stabilizer to enhance structural stability. The improvements are achieved through two mechanisms: restricting the thermal movement of the active site and facilitating lattice oxygen migration. Density functional theory calculations suggest that both CaO and La₂O₃ promote the detachment of lattice oxygen from NiFe₂O₄. Experimental results demonstrate that the NF@CaLa carrier exhibits a total gas production of 857.4 ml/g at 650 °C with a hydrogen selectivity of 50 %, while maintaining stable performance over 50 cycles. The decarbonized Fe-based oxygen carrier modulates the size and morphology of the active nanoparticles through interactions among the active sites, decarbonizer, and stabilizer, which enhances the size effect. Furthermore, the incorporation of CaO shifts the reaction equilibrium, further improving reactivity. The stabilizer, La₂O₃, ensures the structural integrity of the oxygen carrier throughout the cycling process.