CeO₂ modification-induced spinel NiFe₂O₄ structural evolution and in situ Ni exsolution for Ni-O-Ce Interface...

A series of CeO₂-modified NiFe₂O₄ composite catalysts was prepared by a sol-gel combustion synthesis (SGCS) method, and their CO₂ methanation performance and reaction pathways were investigated. The inverse spinel NiFe₂O₄ phase served not only as a structurally stable catalytic framework but also as an effective precursor for the uniform exsolution and dispersion of active Ni species during reduction, thereby providing a robust basis for interfacial active-site construction. Among all samples, 10% CeO₂-modified NiFe₂O₄ (10Ce-NF) exhibited the best low-temperature activity, achieving 83% CO₂ conversion and nearly 100% CH₄ selectivity at 325 °C, while maintaining good catalytic activity during the 100 h stability test and five thermal cycling stability tests under practical operating conditions. Structural characterizations indicated that CeO₂ modification facilitated Ni species reduction, enhanced oxygen-vacancy concentration, and formed a stable Ni-O-Ce interfacial structure, while effectively inhibiting Ni nanoparticle aggregation. H₂-TPR, XPS, and CO₂-TPD results collectively revealed that CeO₂ modification enhanced reducibility, enriched oxygen vacancies and weak/medium basic sites, and thus improved CO₂ adsorption and activation. DFT calculations further confirmed that the Ni-O-Ce interface significantly lowered CO₂ adsorption energy and strengthened interfacial electronic coupling, thereby facilitating CO₂ activation. In situ DRIFTS showed that CH₄ formation over 10Ce-NF mainly followed a formate-dominated pathway accompanied by the parallel participation of linear CO, whereas NiFe₂O₄ mainly followed an RWGS-dominated CO route. Overall, CeO₂ modification promotes the formation of Ni-O-Ce interfacial sites and oxygen vacancies, thereby enhancing CO₂ activation and improving low-temperature methanation performance over spinel NiFe₂O₄ catalysts.