CeO2 modification-induced spinel NiFe2O4 structural evolution and in situ Ni exsolution for Ni-O-Ce Interface construction to promote CO2 methanation.

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.