Role of alkali metal in maintaining iron integrity during direct CO₂ hydrogenation

Iron catalysts have been extensively investigated for the direct hydrogenation of CO₂ into light olefins and long-chain hydrocarbons. However, rapid catalyst deactivation is caused by the reoxidation of iron carbides to iron oxides by water. In this study, we developed a highly stable iron catalyst to produce high-yield liquid hydrocarbons (C₅₊). The presence of excess Na (20 wt%) as a promoter in the iron-aluminum oxide (FeAlO_x) catalyst facilitated the formation of highly aggregated, highly crystalline metallic iron particles during reduction, which in turn produced large Hägg carbide core-Fe₃O₄/AlO_x shell particles during CO₂ hydrogenation. Excess Na maintained the integrity of these core-shell particles over 2000 h on stream, resulting in a very low C₅₊ yield decay rate (0.005 % h⁻¹). Thus, Na was proposed to act as a structural promotor that maintains the integrity of iron domains during direct CO₂ hydrogenation by suppressing particle pulverization and water reoxidation.