Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

Partial oxidations of small molecules over metal surfaces are central to many heterogeneously catalyzed reactions. However, the identity of the actual surface species that promote or hinder these reactions has remained elusive for a variety of reasons. Recently, the understanding of the role of surface oxides in catalytic activity has changed. Instead of being thought of as poisons, they are now believed to be effective promoters of selective catalysis.

Rhodium (Rh) effectively promotes oxidation reactions and is a benchmark system for models of heterogeneously catalyzed chemistry. For this reason, Rh(111) was chosen as the model system for this dissertation work. The uptake of oxygen on Rh(111) was fully characterized for coverages from 0.5 monolayers (ML) to over 8 ML. The surface oxygen coverage was determined with Auger electron spectroscopy (AES), total oxygen abundance with temperature programmed desorption (TPD), and the surface structures with low energy electron diffraction (LEED) and scanning tunneling microscopy (STM).

Careful control of the exposure parameters allowed for the selective growth of the RhO2 surface oxide, surface adsorbed oxygen, and subsurface oxygen. Following surface oxide growth, the Rh crystal was exposed to carbon monoxide (CO) to study CO oxidation as a probe reaction. Carbon dioxide (CO2) yield was measured using TPD, and surface structure evolution was tracked using STM. This is the first study that shows atomically resolved structural information regarding CO oxidation on RhO2, and reveals conclusive structural evidence of low temperature CO oxidation on RhO2 under UHV conditions.

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