Degree

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Document Type

Dissertation

Abstract

Ceria is an earth-abundant material that has been widely used in heterogeneous catalysis, environmental catalysis, and energy applications thanks for its ability to readily convert between different oxidation states. The objective of this study is to theoretically elucidate the reaction mechanisms for the conversion of model organic compounds on ceria, in order to gain insights for the design of cost-effective and selective ceria-based catalysts. Acetaldehyde, acetic acid, and para-nitrophenyl phosphate monoester were selected as the model compounds to probe ceria surfaces. Density functional theory calculations can provide accurate predictions of adsorption and reaction energetics, which can be used to calculate the necessary kinetic parameters in the microkinetic model that can validate hypothesized reaction mechanisms. This methodology is also able to generate additional insights regarding the dominant surface species, the existence of transient surface species, and the role of active sites such as defects. Based on the spectroscopic evidence from surface science experiments, we were able to validate the proposed reaction mechanism for temperature programmed desorption of acetaldehyde and acetic acid on ceria surfaces. Particularly, the catalytic role of surface oxygen vacancy during the formation of ethylene, acetylene and crotonaldehyde in the AcH-TPD was examined. The desorption of crotonaldehyde is found to be the rate-limiting step. However, pre-existing oxygen vacancy is not required in the AA-TPD due to facile surface reduction induced by deprotonation of acetic acid. We found the ketene pathway was energetically more favorable than the acetone pathway under UHV condition. Our results showed that ceria can be effective in the dephosphorylation of selected monoesters including p-NPP, due to facile P-O ester bond scission. However, the subsequent step-wise hydration is found to be rate-limiting.

Date

10-23-2018

Committee Chair

Xu, Ye

Available for download on Wednesday, January 01, 2020

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