Date of Award
Open Access Dissertation
Chemistry and Biochemistry
College of Arts and Sciences
Donna A. Chen
Heterogeneous catalysis plays a vital role in the commercial production of chemicals. However, much is still unknown about the fundamental surface chemistry involved in catalyst preparation and the surface chemistry of the catalysts themselves. In the first part of this work, a surface science approach was employed to develop a fundamental understanding of the surface chemistry of strong electrostatic adsorption (SEA) of metal precursors on a model carbon support, highly oriented pyrolytic graphite (HOPG). SEA is a wet impregnation method in which anionic/cationic metal precursors are adsorbed onto positively/negatively charged functional groups by adjusting the pH of the solution above or below the point of zero charge of the support. The precursors are subsequently reduced to generate small, well-dispersed nanoparticles. Our findings show that hydroxyl groups on the surface of HOPG mediate the adsorption of Pt and Pd cationic precursors by deprotonating under basic conditions and accumulating a negative charge. In the case of Pt and Pd anionic precursors, hydroxyl groups did not mediate the adsorption of the precursors under acidic conditions. Moreover, the adsorption of the Pt anion was not purely electrostatic and most likely involves a chemical interaction with the support. The reduction of Pt precursors adsorbed onto HOPG lead to the formation of dendritic like clusters, indicative of Pt being highly mobile on the surface and having a weak interaction with the support. The addition of hydroxyl groups did not influence the nucleation of Pt for either precursor.
In the second part of this work, model surfaces were prepared and characterized under ultra-high vacuum conditions, enabling excellent control over the surface composition and morphology of the sample. Re clusters of varying sizes were grown on HOPG to help distinguish between cluster size effects and chemical interactions between Re and oxygen on TiO2(110). Our findings suggest there is indeed a strong chemical interaction that takes place between Re and oxygen on TiO2(110). Lastly, the oxidation states of Re in PtRe catalysts may play an important role in the aqueous phase reforming of oxygenated hydrocarbons and the water gas shift reaction. To understand how the presence of Pt may facilitate the oxidation state of Re, XPS was used to determine the oxidation states that were present on Re films grown on Pt(111) after exposure to oxygen. Based on these studies, it was concluded that the presence of Pt does not facilitate the oxidation of Re films.
Seuser, G. S.(2018). Understanding The Adsorption And Nucleation Of Transition Metals On A Model Carbon Support. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/4878