Ambient-Pressure CO ₂ Hydrogenation to Light Olefins Over Calcium-Modified FeMnK Catalysts: Fe ₃ O ₄ /Fe ₅ C ₂ Phase Balance and Electron Enrichment Effects

Achieving high selectivity to light olefins from CO2 hydrogenation under ambient pressure remains challenging due to unfavorable phase dynamics and excessive RWGS activity in iron-based catalysts. Comprehensive characterization reveals that moderate Ca addition inhibits water-induced oxidation of Fe5C2, stabilizes carbide phases, promotes electron transfer from CaCO3 to Fe species, and enhances CO transferfrom Fe3O4 (RWGS sites) to Fe5C2 (FTS sites). These effects synergistically suppress CO and CH4 formation while facilitating C–C coupling. The optimized Ca8K8FeMn catalyst delivers 26.9% CO2 conversion, 68.6% CO selectivity, 59.3% light olefins selectivity in hydrocarbons, and a space-time yield of 33.5 gC2‐C4=kgcat‐1h‐1 at 320 °C, 0.1 MPa, H2/CO2 = 3, GHSV = 3600 mL·g–1·h–1. Compared to the unmodified K8FeMn, CO selectivity decreases by ∼30%, CH4 by ∼10%, light olefins selectivity increases by 7.7%, and STY improves 6-fold. This work elucidates the critical roles of phase equilibrium and electronic modulation in ambient-pressure CO2-to-olefins catalysis.