Analytical model of CeO₂ oxidation and reduction

In this work, an Arrhenius-based model for the high-temperature reduction and oxidation of CeO₂ is developed. The model is shown to agree well with both literature data for the equilibrium oxygen vacancy concentration and novel experimental kinetics of oxidation and reduction obtained by the authors. The form of the Arrhenius rate equation was determined from the properties of the reaction. Equilibrium data from the literature was analyzed with respect to our rate equation. From this analysis, a number of constraints on the model parameters were determined, and some of the constants of the model were fixed. The model accurately predicts the equilibrium composition of CeO₂ over a wide range of oxygen partial pressures (10^-2 to 10 ^-8 bar) and temperatures (1000-1900 C). Novel results of the experimental reoxidation of ceria were analyzed to fix the remainder of the constants. Porous cerium dioxide pellets produced by the authors were reduced at high temperature (1650 C) and low oxygen partial pressure (10^-5 bar). The reduced cerium pellets were then reoxidized in an oxygen atmosphere of 1.4 × 10^-4 bar at temperatures in the range 500-1000 C. The reoxidation was conducted in a sealed vacuum chamber. The reaction was monitored via the change in pressure and gas composition measured by a manometer and mass spectrometer. The results from this reoxidation experiment allowed us to fix the values of the activation energies and frequency factors of the oxidation and reduction. The model was then compared with experimental reaction kinetics of thermal oxidation and reduction and showed good agreement.