Heterocoordination-driven regulation of Ca₂Fe₂O₅ lattice oxygen for high selectivity syngas and hydrogen production via chemical looping

Regulating lattice oxygen in metal oxides to balance methane C–H activation and syngas selectivity in the chemical looping steam methane reforming (CLSMR) process remains a significant challenge. This study investigates the effects of B-site doping of Ni, Co, and Al in the Ca₂Fe₂O₅ oxygen carrier, focusing on the impact of Al doping concentration on reaction selectivity and activity. The results demonstrate that moderate Al doping effectively introduces oxygen vacancies, significantly increasing the proportion of surface-adsorbed oxygen and selective oxygen, thereby promoting partial oxidation. At 850 °C, the Ca₂Fe_1.4Al_0.6O₅ oxygen carrier exhibits excellent performance, achieving a CO selectivity of 95.48 %, a syngas yield of 6.94 mmol g⁻¹, and a hydrogen yield of 3.16 mmol g⁻¹, with nearly no carbon deposition observed. Density Functional Theory (DFT) calculations indicate that, at an Al doping concentration of 0.2, oxygen vacancies in the Fe-O-Al (3.11 eV) structure are more stable than those in the Fe-O-Fe (3.01 eV) structure. As the Al doping concentration increases to 0.6, the formation energy of oxygen vacancies further decreases (Fe-O-Al: 1.81 eV), lowering the reaction energy barrier, thus facilitating oxygen transport and enhancing reaction activity. This study provides theoretical and innovative strategies for the high-selectivity production of syngas and hydrogen.