[CCoE Notice] Cullen College Dissertation Defense Announcement - Sadia Afrin

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[Dissertation Defense Announcement at the Cullen College of Engineering]

Insights into ceria reduction and the roles of oxygen-vacancies in redox and acid-catalyzed reactions over ceria surfaces



Sadia Afrin

April 8, 2022; 12:30-2:30 PM (CST)
Location: AERB 320



Committee Chair:
Praveen Bollini, Ph.D.

Committee Members:
Michael Harold, Ph.D. | Vincent Donnelly, Ph.D. | Robert Comito, Ph.D. | Kaiwalya Sabnis, Ph.D.

Abstract

     Cerium oxide is a versatile catalyst that is well known for its propensity to undergo rapid reduction-oxidation cycles in response to exposure to sub and over-stoichiometric amounts of oxygen, respectively. We investigate different classes of surface reactions to assess the origin of catalytic functionality of ceria surfaces based on qualitative and quantitative kinetic analyses. Bulk cerium oxide is found to catalyze anisole hydrodeoxygenation at 698K and ambient pressures of hydrogen with high selectivity towards benzene, demonstrating its utility toward reducing oxygen content of biomass derived oxygenates with a high hydrogen efficiency. Quantitative analyses of four sets of aerobic/anaerobic ethanol conversion transients point to the evolution of a native high surface area cerium oxide surface due to the reduction half of the ethanol oxidation turnover to catalyzing, exclusively, non-oxidative ethanol dehydrogenation upon complete surface reduction. We quantify and exploit the existence of a well-defined peak near 2150 cm-1 corresponding to the 2F5/2 to 2F7/2 electronic transition of reduced cerium, and demonstrate its utility in the quantification of oxygen vacancy concentrations during the occurrence H2-D2 exchange and tert-butanol dehydration catalysis over ceria surfaces. Mechanistic analyses for ethene hydrogenation over H2-treated ceria surfaces suggest the prevalence of rate determining sequential H-addition steps involving multiple active sites, as well as an optimum density of active sites for the maximization of areal rates. Lastly, overestimation of active site densities due to unselective adsorption during breakthrough experiments has been demonstrated using in-situ CO titrations, and methods for the interpretation of such titration data that can provide meaningful information discussed. Overall, the work conducted as part of this dissertation advances our understanding of the precise catalytic function of oxygen understoichiometry on reducible metal oxide surfaces.



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