Enhanced oxygen storage capacity of CeO2 with doping-induced unstable crystal structure

Abstract

Doping CeO2 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 CeO2 from the perspective of crystallography. In the present study, we improved the OSC by construction of an extremely unstable CeO2 crystal structure based on crystallographic principles. By doping CeO2 with smaller Hf4+ and Sn4+ 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 Hf4+ and Sn4+, respectively. Our results showed that smaller dopant cations (radius of Sn4+ < Hf4+) led to more vacancies. The low temperature OSC of a CeO2 sample doped with a saturated amount of Hf4+ was 2.2 times as high as that of undoped CeO2 with a similar BET specific surface area. The partial least squares method was used to construct two linear functions for the Hf4+- and Sn4+-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 CeO2 three-way catalysts.