Understanding the Structure of Ti-Doped Ceria Nanoparticles and Tuning Their Reducibility

Doped ceria-based materials are leading candidates for advanced catalytic applications and fuel cells. To achieve a high oxygen storage capacity (OSC), these materials must simultaneously exhibit robust framework stability and high reducibility, which is driven by the Ce4+/Ce3+ redox cycle. In this work, using density functional theory (DFT) simulations on a Ce140O280 nanoparticle model, we elucidate Ti dopant site preferences and structural evolution under mono-, bi-, and multidoping strategies. The impact of Ti4+ dopants on host reducibility was also evaluated via calculated oxygen vacancy formation energies. Our results reveal that, although ionic radius trends suggest Ti4+ should favor subsurface occupancy, Ti ions undergo surface segregation near (100) facets. This divergence was rationalized by the higher thermodynamic stability of the CeO2 host relative to bulk TiO2. Low-level Ti4+ substitution (one or two ions) into the ceria framework results in significantly enhanced reducibility compared to its Group 4 counterparts (Zr and Hf), thus providing a theoretical foundation for further experimental investigations.