Thermal stability of doped ceria: experiment and modelling

Abstract

The process of the decrease of the surface area due to crystallite growth in ceria at 943 K is described by a kinetic model involving oxygen and cerium diffusion. The experimentally found variations in the rate of crystallite growth are reported as a function of the content (⩽ 10% cat.) of dopants, which are the cations Ca²⁺, Mg²⁺, Al³⁺, Y³⁺, Sc³⁺, Al³⁺, Th⁴⁺, Zr⁴⁺ and Si⁴⁺. The variations are discussed on the basis of the diffusion of cerium vacancies as the rate-limiting step, and on the basis of calculated expressions of the concentrations of oxygen vacancies, electrons and cerium vacancies vs. the oxygen partial pressure and the dopant content. For cations that are smaller than Ce⁴⁺, the comparison between the experimental and theoretical rates asserts the validity of the model and allows the prediction of the efficiency of a cation to stabilize the surface area, from its associations with oxygen vacancies and with the electron-bearing species, Ce′_Ce.