Analytical Model of CeO 2 Oxidation and Reduction

4 ABSTRACT: In this work, an Arrhenius-based model for the 5 high-temperature reduction and oxidation of CeO2 is 6 developed. The model is shown to agree well with both 7 literature data for the equilibrium oxygen vacancy concen8 tration and novel experimental kinetics of oxidation and 9 reduction obtained by the authors. The form of the Arrhenius 10 rate equation was determined from the properties of the reaction. Equilibrium data from the literature was analyzed with respect 11 to our rate equation. From this analysis, a number of constraints on the model parameters were determined, and some of the 12 constants of the model were fixed. The model accurately predicts the equilibrium composition of CeO2 over a wide range of 13 oxygen partial pressures (10−2 to 10−8 bar) and temperatures (1000−1900 °C). Novel results of the experimental reoxidation of 14 ceria were analyzed to fix the remainder of the constants. Porous cerium dioxide pellets produced by the authors were reduced at 15 high temperature (1650 °C) and low oxygen partial pressure (10−5 bar). The reduced cerium pellets were then reoxidized in an 16 oxygen atmosphere of 1.4 × 10−4 bar at temperatures in the range 500−1000 °C. The reoxidation was conducted in a sealed 17 vacuum chamber. The reaction was monitored via the change in pressure and gas composition measured by a manometer and 18 mass spectrometer. The results from this reoxidation experiment allowed us to fix the values of the activation energies and 19 frequency factors of the oxidation and reduction. The model was then compared with experimental reaction kinetics of thermal 20 oxidation and reduction and showed good agreement.