Enhanced oxygen storage capacity of CeO ₂ with doping-induced unstable crystal structure

Doping CeO ₂ with certain metallic ions has been shown to be an effective route to improving its oxygen storage capacity (OSC). We aimed to study the effects of dopants on the OSC of CeO ₂ from the perspective of crystallography. In the present study, we improved the OSC by construction of an extremely unstable CeO ₂ crystal structure based on crystallographic principles. By doping CeO ₂ with smaller Hf ⁴⁺ and Sn ⁴⁺ cations, the incorporated cations produced a lower cation to anion radius ratio in the crystal. The relative oxygen vacancy concentrations were 0.452 and 0.514, respectively, for 3 mol.% doping of Hf ⁴⁺ and Sn ⁴⁺ , respectively. Our results showed that smaller dopant cations (radius of Sn ⁴⁺ < Hf ⁴⁺ ) led to more vacancies. The low temperature OSC of a CeO ₂ sample doped with a saturated amount of Hf ⁴⁺ was 2.2 times as high as that of undoped CeO ₂ with a similar BET specific surface area. The partial least squares method was used to construct two linear functions for the Hf ⁴⁺ - and Sn ⁴⁺ -doping concentration vs. lattice parameters, and the relative oxygen vacancy concentration vs. low temperature OSC per BET surface area. Structure-performance relationships were developed to enable the design of CeO ₂ three-way catalysts.