Oxygen exchange reaction kinetics for cerium(IV) oxide at 1000 °C

Mechanisms and kinetics of the oxygen exchange reaction with CeO2 at high temperatures

“…Previously, we reported extremely rapid and consistent oxygen exchange behavior on a wide variety of CeO 2 powders at 1000°C, and observed that the exchange is independent of oxygen partial pressure, total pressure, and most particle characteristics, including specific surface area (SSA) [10]. The results from this report are intriguing for two reasons.…”

“…When the temperature is ≥ 1000°C, both the − 325 mesh and 70-100 nm samples produce identical rate constants and have an activation energy (E a ) of 11.0 ± 0.4 kJ/mol (0.114 eV). This high temperature, low E a reaction observed was previously determined to be independent of oxygen partial pressure, total pressure, and most particle characteristics including particle size and SSA; leading to the conclusion that the rate is dominated by an internal chemical reaction that is occurring through the bulk and not at the surface of the material [10]. As the temperature decreases below 1000°C, the reaction governing the rate of exchange changes for the − 325 mesh sample with an E a = 29.1 ± 1.2 kJ/mol (0.287 eV).…”

“…Our previous report describes in detail the in-house constructed fused silica reaction chamber with on-line sampling and residual gas analyzer (RGA) mass spectrometric detection that was used to perform all of the oxygen exchange experiments [10]. While this same report also describes the experimental procedure in detail, an abbreviated version of the procedure is also given here.…”

“…While a detailed description of the methods used to analyze this data were also discussed previously [10], we feel it is important to review some of the salient details. First, the derived rate law is:…”

“…It is interesting to note that ThO 2 [2,15] exhibits oxygen exchange behavior similar to CeO 2 at lower temperatures while PuO 2 [16][17][18][19] exhibits oxygen exchange behavior similar to CeO 2 at 1000°C [10]. Similarities in these systems raise an intriguing question: is this novel oxygen exchange behavior the result of chemical similarities between these systems, similarities in the solid state ionic structure, or some combination of chemistry and structure?…”