Oxygen Vacancy-Driven CO2 Adsorption/Activation and Fe5C2 Phase Evolution in Ce-Doped ZnFe2O4 Spinel Catalysts for Enhanced Light Olefins Production

Developing efficient catalysts for CO2 conversion to light olefins via hydrogenolysis-driven C–C coupling remains a critical challenge due to the inherent trade-off between CO2 activation and selective C–C coupling. This study introduces a cerium-doped ZnFe2O4 (CenZFO) spinel catalyst that synergistically enhances CO2 conversion and olefin selectivity through oxygen vacancy (OV) engineering and phase modulation. Incorporating Ce3+ into the ZnFe2O4 lattice induces lattice distortion and Ce3+/Ce4+ redox cycles, increasing oxygen vacancy (OV) concentration from 19.6% in undoped ZFO to 29.3% in Ce1ZFO. Such enhancement facilitates CO2 adsorption (*HCOO stabilization) and suppresses methane formation by inhibiting excessive H2 dissociation. The optimized Ce1ZFO catalyst achieves 38.1% CO2 conversion (290 °C, 2 MPa) with 46.5% C2═–C4═ selectivity and 28.6% C5+ yield, outperforming conventional Fe-based catalysts. In situ characterization and DFT calculations reveal that Ce doping promotes Fe3O4 → Fe5C2 transformation, lowering the energy barrier for *HCOO hydrogenation by 19.6% (1.89 vs 2.35 eV) and stabilizing Fe5C2 phases critical for chain growth. The spinel framework inhibits Fe5C2 sintering, ensuring 70 h stability with <5% activity loss. Mechanistic studies identify dual-site activation: OV-rich Ce–O–Fe interfaces drive CO2 dissociation, while electron-deficient Fe sites enable selective C–C coupling. This work establishes a universal design principle-dopant-induced OV generation coupled with phase control─for bridging CO2 activation and olefin synthesis, offering a scalable route to sustainable hydrocarbon production. The catalyst's space-time yield (4.01 mmol·g–1·h–1) and low methane selectivity position it as a promising solution for carbon-neutral chemical manufacturing.