Master of Science (MS)
Geology and Geophysics
Ceria (CeO2) is a fluorite type oxide that has been used extensively as an oxygen storage media in three-way catalysts, as an oxygen partial pressure regulator, as a fuel additive for the reduction of soot and for the production of syn-gas from water and carbon dioxide. It is known that exposing ceria powders to low pO2 and/or high temperature conditions will cause ceria to partially reduce. This partial reduction leads to the formation of oxygen vacancies, which up to a limit, do not significantly influence the crystal structure. When partially reduced ceria is exposed to high pO2 environments, such as open air, the ceria powders will readily reoxidize even at room temperature. The reoxidation effectively fills the oxygen vacancies with new oxygen. To analyze this process, we have devised an experimental procedure utilizing triple oxygen isotope labeled initial ceria powders. These powders are heated (700°C) and cooled under vacuum prior to exposure to air. By combining the results from independent experimental sets using different initial oxygen isotope labels we have determined the kinetic isotope fractionation factors for both high temperature reduction and low temperature reoxidation using a graphical method. Our results indicate that there is a 1.5‰ ±0.8‰ increase in the δ18O value of the remaining ceria upon heating in vacuum at 700°C for one hour. When the vacuum is broken at room temperature, the heated ceria will take in 3% to 19% oxygen from air, with a δ18O of 2.6‰ (-5.3‰; +8.3‰). These fractionation factors are consistent with a kinetic fractionation model. The issue associated with room-temperature reoxidation renders ceria a poor choice of exchange medium for oxygen isotope analysis of CO2 or other oxygen-bearing gases.
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Hayles, Justin Alan, "The reduction and reoxidation of ceria : a natural abundance oxygen isotope approach" (2013). LSU Master's Theses. 2671.