Experimental and theoretical studies reveal performance descriptors and provide molecular-level understanding of HCl oxidation over CeO₂. Steady-state kinetics and characterization indicate that CeO₂ attains a significant activity level, which is associated with the presence of oxygen vacancies. Calcination of CeO₂ at 1173 K prior to reaction maximizes both the number of vacancies and the structural stability of the catalyst. X-ray diffraction and electron microscopy of samples exposed to reaction feeds with different O₂/HCl ratios provide evidence that CeO₂ does not suffer from bulk chlorination in O₂-rich feeds (O₂/HCl ? 0.75), while it does form chlorinated phases in stoichiometric or sub-stoichiometric feeds (O₂/HCl ? 0.25). Quantitative analysis of the chlorine uptake by thermogravimetry and X-ray photoelectron spectroscopy indicates that chlorination under O₂-rich conditions is limited to few surface and subsurface layers of CeO₂ particles, in line with the high energy computed for the transfer of Cl from surface to subsurface positions. Exposure of chlorinated samples to a Deacon mixture with excess oxygen rapidly restores the original activity levels, highlighting the dynamic response of CeO₂ outermost layers to feeds of different composition. Density functional theory simulations reveal that Cl activation from vacancy positions to surface Ce atoms is the most energy-demanding step, although chlorine-oxygen competition for the available active sites may render re-oxidation as the rate-determining step. The substantial and remarkably stable Cl₂ production and the lower cost of CeO₂ make it an attractive alternative to RuO2 for catalytic chlorine recycling in industry.