USING FUNDAMENTAL SURFACE SCIENCE STUDIES TO DEVELOP STATEGIES FOR DESIGNING CHEMICAL SYSTEMS

Abstract

The works presented in this dissertation are organized into five parts. Part I - Temperature-Programmed Spectroscopy (TPS): A Novel Tool for Surface Kineticand Mechanistic Studies Part I presents a series of innovative experimental techniques designed to validate theoreticalcalculations for surface kinetic systems. Known collectively as temperature-programmed spectroscopy, these analytical tools can be utilized by a variety of spectroscopic techniques to detect subtle changes over short time intervals, facilitating the measurement of kinetic properties for surface-based processes. This approach provides a means of experimentally testing theoretical values that were previously unverifiable. The techniques described in Part I can be used to refine pseudopotentials and other parameters in computational chemistry by benchmarking against calculated values for elementary step reactions using experimental data. Furthermore, this collection of analytical methods is valuable for mechanistic studies of both elementary reactions as well as more complex processes involving multiple activation barriers. Notably, these methods enable the study of surface processes without requiring the desorption of gas-phase products, broadening their applicability in heterogeneous chemistry research. Part II - Using Fundamental Studies to Define Systems for Mechanochemical Studies:Probing the Relationship Between Terminus-Counterface Interactions and Tribological Decomposition Part II focuses on utilizing surface-selective techniques to investigate chemical states onsurfaces for further mechanochemical studies. Mechanochemistry, the study of chemical reactions initiated by mechanical forces, is one of the oldest branches of chemistry yet remains among the least understood. A particularly economically and technologically significant aspect of mechanochemistry is tribology—the study of friction, wear, and lubrication between sliding surfaces. It has been reported that approximately one-third of automotive fuel is wasted in overcoming friction within the system. Advances in tribology and lubrication technologies have the potential to reduce this waste, offering substantial economic benefits by decreasing fuel consumption in both the transportation and energy sectors, potentially saving billions of dollars annually in the United States through reduced production demands. Despite the field's underdeveloped theoretical foundation, there has been a surge in mechanochemical synthesis publications, highlighting its industrial potential. Part II of this dissertation investigates the relationship between terminus-counterface interactions and tribological decomposition. It begins by employing surface-selective techniques to characterize the orientation, structure, and thermal chemistry of various chemical systems. These findings are then correlated with tribological results to test theories linking the strength of termini-counterface interactions with the rate of tribological decomposition. Furthermore, first-principles density functional theory (DFT) calculations are employed to examine variables that may enhance or diminish termini-counterface interactions, providing insights into how these interactions can be tuned to control the rate of tribological decomposition. Part III - Fundamental Studies of Chiral Modification of Heterogeneous Reactions:Designing Strategies for Tuning Enantioselectivity Part III of this dissertation focuses on the chiral modification of chemical reactions on catalystsurfaces to investigate the mechanisms by which enantioselectivity is imparted. This research aims to understand how chirality is conferred and explores the relationship between enantioselectivity and reaction rate enhancement. The investigation began by employing surface-selective techniques to elucidate the mechanism by which a selected chiral modifier imparts enantioselectivity during the hydrogenation of methyl pyruvate to produce methyl lactate, a chiral compound. This mechanistic understanding was then used to develop a model testing whether the observed enantioselectivity in a heterogeneous reaction arises from the ratio of pro-chiral binding structures on the catalyst surface. The hypothesis was subsequently tested using both flow and batch reactors on single crystal catalysts as well as supported catalysts. Part IV - Fundamental Studies in Green Chemistry: Tuning Chemical Selectivity ofHeterogeneous Reactions Using Surface Modifiers Part IV of this dissertation is focused on developing the fundamental understanding of thelateral interactions of selected molecules during chemical reactions. The objective of this research is to tune the chemical selectivity by introducing surface organic modifiers into reaction mixtures. The potential application of this work lies in strategically altering chemical selectivity to reduce waste production, a key priority in green chemistry efforts. Minimizing waste, especially that which has significant environmental impact, aligns with the principles of a sustainable industry. An important benefit of using strongly binding organic modifiers is their ability to enhance chemical selectivity, thereby reducing the need for costly chemical separation processes and limiting the formation of undesirable byproducts. This section employs several surface-selective techniques as well as high-pressure gas-phase heterogeneous reactions to explore lateral interactions between selected organic modifiers and their impact on chemical selectivity during furfural hydrogenation reactions over model Pd(111) single crystal catalysts. The studies examine various types of surface organic modifiers and detail the mechanisms by which each influences chemical selectivity. These findings demonstrate how such modifiers can effectively minimize unwanted byproduct formation during chemical synthesis. By providing strategies to optimize reaction pathways, this research contributes to the development of more efficient and environmentally friendly chemical processes. Part V - Using Fundamental Surface Science Studies to Develop Strategies for the Design ofMolecular Electronic Circuits Part V of this dissertation focuses on leveraging fundamental surface studies to developstrategies for designing molecular electronics circuits. A primary objective in technological research and development is to create increasingly smaller device components. The advantages of miniaturization are substantial, including increased component density, faster processing speeds in computers, reduced power consumption that extends battery life, and lighter, more portable devices. Additionally, smaller components enable more efficient use of raw materials, allowing greater production on a single silicon wafer. However, there are limits to how much device density can be increased. Beyond a certain point, current etching methods become impractical, marking a deviation from Moore’s Law. Addressing this challenge may require adopting a "bottom-up" approach, where devices are built from molecular components rather than being etched from bulk materials. Part V of this dissertation employed surface-selective techniques to explore strategies for fabricating molecular electronic devices with asymmetric conductivity. These strategies were grounded in a fundamental understanding of self-assembly processes, offering a plausible pathway to overcome the limitations of traditional miniaturization methods.