Ni-Fe bimetallic hexaaluminate for efficient reduction of O₂-containing CO₂ via chemical looping

Direct utilization of impure CO ₂, especially with O ₂ impurities, bridges the technology gap between carbon capture and utilization (CCU), by reducing the overall carbon footprint. In this work, we developed Ni-substituted LaFe ₃Al ₉O ₁₉ hexaaluminates as oxygen carriers to efficiently reduce CO ₂ into high value-added substances, with the presence of a large amount of O ₂ impurities via a chemical looping scheme. With O ₂ to CO ₂ ratio of 0.857:10, LaFe _2.9Ni _0.1Al ₉O ₁₉ exhibited high CO ₂ conversion of ∼ 92% and synthesis gas yield of ∼ 4.26 mmol/g with a suitable H ₂/CO ratio (∼ 2.0) during the redox cycles. Even with extremely high content of O ₂ (O ₂ to CO ₂ ratio of 38:10), an acceptable CO ₂ conversion (over 50%) and synthesis gas yield (∼ 3.84 mmol/g, H ₂/CO ratio, ∼ 2.0) were obtained. These results benefited from the synergistic effect of Ni and Fe that low amounts of Ni sufficed to activate methane splitting and Fe increased the resistance to coke formation during CH ₄ partial oxidation. Meanwhile, in O ₂-containing CO ₂ splitting step, Ni-Fe bimetallic hexaaluminate enhanced the ability of the oxygen carriers to activate CO ₂ and suppressed the oxidative competition of O ₂ compared with pure Fe hexaaluminate. Our work presents a promising approach for direct utilization of impure CO ₂ and achieving carbon–neutral economic development.