Developing a fundamental understanding of the interactions between catalytic surfaces and adsorbed molecules is imperative to the rational design of new materials for catalytic, sorption and gas separation applications. Experiments that probed the chemistry at the gas-surface interface were employed through the utilization of in situ infrared spectroscopic measurements in high vacuum conditions to allow for detailed and systematic investigations into adsorption and reactive processes. Specifically, the mechanistic details of propene epoxidation on the surface of nanoparticulate Au supported on TiO2 and dimethyl chlorophosphate (DMCP) decomposition on the surface of TiO2 aerogel-supported Cu nanoparticles were investigated. In situ infrared spectroscopy illustrates that TiO2-supported Au nanoparticles exhibit the unprecedented ability to produce the industrially relevant commodity chemical, propene oxide, through the unique adsorption configuration of propene on the surface of Au and a hydroperoxide intermediate (-OOH) in the presence of gaseous hydrogen and oxygen. Whereas, TiO2-supported Cu aerogels oxidize the organophosphate-based simulant, DMCP, into adsorbed CO at ambient environments. Through a variety of spectroscopic methods, each step in these oxidative pathways was investigated, including: adsorption, oxidation and reactivation of the supported-nanoparticle systems to develop full mechanistic pictures. Additionally, the perturbation of vibrational character of the probe molecule, CO, was employed to characterize the intrinsic µ3-hydroxyls and molecular-level defects associated with the metal-organic framework (MOF), UiO-66. The adsorption of CO onto heterogeneous surfaces effectively characterizes surfaces because the C-O bond vibrates differently depending on the nature of the surface site. Therefore, CO adsorption was used within the high vacuum environment to identify atomic-level characteristics that traditional methods of analysis cannot distinguish. / Doctor of Philosophy / The interaction between small gas molecules and solid surfaces is important for environmental, industrial and military applications. In order to chemically change molecules, surfaces act to lower activation barriers and provide a low energy plane to create new chemical bonds. To study the fundamental interactions that occur between gas molecules and surfaces, we employ infrared spectroscopy in order to probe the vibrations of bonds at the gas–surface interface. By tracking the chemical bonds that break and form on the surface of different materials, we can develop surface reaction pathways for a variety of different chemical reactions. We focus our efforts on two different applications: the conversion of propene to propene oxide for industrial applications and the decomposition of chemical warfare agents. Using the techniques described above, we were able to develop reaction pathways for both propene oxidation and chemical warfare agent simulant degradation. Our work is critical to the further development of catalysts that harness the specific structural and chemical properties we identify as important and exploit them for further use.

Chemical warfare agents are a toxic class of compounds that are incredibly harmful to human health. Methods of detoxification and decontamination currently exist, however they all suffer from problems that involve logistical transport or involve technologies that directly address liquid threats instead of vapors. One promising method of detoxification involves the oxidation of these compounds into less-harmful species. The relatively large chemical size and complexity of modern-day chemical warfare agents, however, precludes a straightforward analysis of the chemical transformations that take place on novel decontaminating materials. Additionally, a fundamental understanding of reaction mechanisms that occur on novel material surfaces is required before improved materials can be developed. To this end, the oxidation of three simpler, smaller organic molecules were studied over a variety of materials in order to build up a chemical understanding of the systems under study. The photoepoxidation of propene into propene oxide was observed to readily occur over an in-house developed dual titania-silica catalyst created by atomic layer deposition. The subsequent photoinduced degradation of produced propene oxide was observed to occur over the novel catalyst. Next, the oxidation of CO was studied over a Pt/TiO2 catalyst while in the presence of humidity. The addition of water was shown to enable an alternative, low energy pathway that closely followed the water gas shift, but ended upon the production of stable surface-bound formates. Gaseous oxygen was found to subsequently oxidize these surface formates into the full oxidation product, CO2. Next, the oxidation of methanol was studied over the same Pt/TiO2 catalyst. It was discovered that the water produced when methanol initially adsorbs to the catalyst surface is responsible for unlocking the oxidative capacity of the material. Finally, a custom packedbed reactor was designed and built that enabled unique experimental capabilities not yet available in commercial systems, and will be used in the future to directly test the oxidative capabilities of novel materials for chemical warfare agent destruction. / Doctor of Philosophy / The chemical interactions and reactions that occur between gases and surfaces are incredibly important for a multitude of technologies employed by governments, militaries, and citizens alike. The precise methods in which these gases interact with materials of interest determine whether said material can be used in a catalytic fashion. Much like how an automobile catalytic converter does not have to be replaced each time the vehicle is started; a catalyst is able to be used repeatedly without loss of function. Catalysts in general are unique in that they function to create or allow for chemical reactions to proceed through alternative, lower energy pathways that are more likely to occur under milder environmental conditions. In order to understand the chemical reactions that occur on a catalyst, a combination of specialized spectroscopic methods was used that allowed for tracking the precise chemical bonds that were formed or broken during reaction. A few different model chemical reactions are explored in this work, ranging from the conversion of carbon monoxide into CO2, and the oxidation of methanol, a small alcohol commonly found in fuel cells. The experimental techniques employed herein allowed for precise chemical mechanisms to be tracked, and the information gained will certainly be useful for the design of next-generation materials by future research.