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 (Ce_nZFO) spinel catalyst that synergistically enhances CO₂ conversion and olefin selectivity through oxygen vacancy (O_V) engineering and phase modulation. Incorporating Ce³⁺ into the ZnFe₂O₄ lattice induces lattice distortion and Ce³⁺/Ce⁴⁺ redox cycles, increasing oxygen vacancy (O_V) 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: O_V-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 O_V 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.