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Ceria is widely used in heterogeneous catalysis owing to its redox properties. Engineering the shape of ceria particles offers a powerful tool to develop materials with enhanced catalytic properties. In this study, we provide evidence for the shape-dependent dioxygen adsorption and activation of ceria nanoparticles with (111) and (100) facets by in situ Raman spectroscopy and relate these properties to unique adsorption sites employing density functional theory. Temperature- and gas-phase-dependent experiments demonstrate facilitated formation of peroxide, superoxide, and weakly bound dioxygen species on the (100) facets as rationalized by calculated vibrational frequencies of O₂²⁻, O₂⁻, and O₂ species on CeO₂₋ₓ(100) surfaces. Our results show that localization of the excess charge, driving the Ce⁴⁺ → Ce³⁺ reduction, significantly affects the stretching vibrations. Our approach provides a powerful basis for future developments of ceria-based catalysts by bridging the materials gap between idealized and real catalytic systems.