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

Abstract

Direct utilization of impure CO2, especially with O2 impurities, bridges the technology gap between carbon capture and utilization (CCU), by reducing the overall carbon footprint. In this work, we developed Ni-substituted LaFe3Al9O19 hexaaluminates as oxygen carriers to efficiently reduce CO2 into high value-added substances, with the presence of a large amount of O2 impurities via a chemical looping scheme. With O2 to CO2 ratio of 0.857:10, LaFe2.9Ni0.1Al9O19 exhibited high CO2 conversion of ∼ 92% and synthesis gas yield of ∼ 4.26 mmol/g with a suitable H2/CO ratio (∼ 2.0) during the redox cycles. Even with extremely high content of O2 (O2 to CO2 ratio of 38:10), an acceptable CO2 conversion (over 50%) and synthesis gas yield (∼ 3.84 mmol/g, H2/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 CH4 partial oxidation. Meanwhile, in O2-containing CO2 splitting step, Ni-Fe bimetallic hexaaluminate enhanced the ability of the oxygen carriers to activate CO2 and suppressed the oxidative competition of O2 compared with pure Fe hexaaluminate. Our work presents a promising approach for direct utilization of impure CO2 and achieving carbon–neutral economic development.