Direct In Situ TEM Visualization of Atom Migration in SiO2-Coated Core-Shell NiFe2O4 Redox Catalyst During Chemical Looping CO2 Conversion.

Chemical looping technology utilizes the redox process and catalytic effects of metal oxides to convert carbon-containing fuels and carbon dioxide into value-added chemicals. Currently, cation diffusion, sintering, agglomeration, and the inactivation of metal oxides during cyclic redox reactions are the key challenges hindering the widespread industrialization of the chemical looping. While encapsulation strategies using supports have shown potential for prolonging redox catalyst lifespan, the fundamental mechanisms of support-redox catalyst interactions and deactivation pathways under prolonged cycling remain elusive. In this study, the varying structural evolution pathways of redox catalysts from in situ transmission electron microscopy (TEM) indicate that the SiO2 shell can suppress Ostwald ripening during the reduction process through a confinement effect, thereby preventing the agglomeration of metal particles. Moreover, the activity-related size-dependent of Ni nanoparticles is elucidated through density functional theory (DFT) simulations. SiO2 support affects the migration path during the oxidation process. Finally, redox catalysts struggle to remain stably embedded within support or securely anchored on their surfaces. The continuous separation between Ni-Fe and support may serve as a critical factor in deactivation in the long-term. This study offers new insights into designing hierarchical redox catalysts with enhanced thermal and redox stability through in situ observation of the actual reaction process under high-temperature.