(400a) The Oxidation Kinetics of Two Step Solar Thermochemical H2O and CO2 Splitting with CeO2

The two step solar thermochemical H₂O and CO₂ splitting with CeO₂ has been investigated. We observe that the thermal reduction process of CeO₂, to form the nonstoichiometric CeO_2-δ, is fast for particles of order 5 µm diameters. Furthermore, we introduce a novel numerical model fitting method to implement solid state kinetics theory to study the oxidation process of CeO_2-δ. The advantage of this method is that the kinetic parameters obtained are fitted over the complete conversion range and not limited to a specific range of reaction extent. We are unaware of this methodology used to analyze high temperature ceria kinetics elsewhere in the literature.

The objective of the kinetic analysis is to determine the intrinsic kinetic parameters of the oxidation process: energy of activation (E_a), reaction mechanism (f(α)), and oxidant concentration dependence (γ). In this work, we determine that the oxidation of CeO_2-δ by H₂O and CO₂ is surface reaction limited in the range of 0 < d < 0.04. The H₂O oxidation kinetics can be modeled very well; the kinetic parameter for the water splitting reaction is reported. CO₂ oxidation on the other hand, cannot be adequately described by a simple application of solid state kinetic theory because it fails to describe the complete temporal behavior of the CO evolution process.