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The targeted design of new catalyst materials can only be accomplished once a fundamental understanding of the interactions between material surfaces and adsorbed molecules is developed. In situ infrared spectroscopy and mass spectrometry methods were employed to probe interactions at the gas-surface interface of oxide-supported metal nanoparticle materials. High vacuum conditions allowed for systematic investigations to describe detailed reaction mechanisms. Specifically, variable temperature infrared spectroscopy was utilized to uncover the binding energetics of CO to the oxide surface of TiO2-based materials. As binding energetics are related to the electronic structure of the adsorption site, differences in evaluated binding enthalpies are hypothesized to probe electronic metal-support interactions that describe charge transfer between the supported metal nanoparticles and TiO2. Cu/TiO2 aerogels were identified as a candidate for more in-depth studies. Flow reactor methods in combination with the surface-based infrared spectroscopy were utilized to elucidate the CO oxidation reaction mechanism over Cu/TiO2 aerogels. Bridging oxygen atoms on TiO2 regions of the material were identified as the active site for catalysis in a Cu-assisted Mars-van Krevelen lattice extraction mechanism. Methanol oxidation was then studied with similar methods to show the complete conversion to CO2 and H2O at high temperatures through the reduction of titania and formation of a formate intermediate. Higher-order carbonaceous alcohols were probed for adsorption and reactivity on Cu/TiO2 aerogels and were observed to follow a similar reaction pathway. The higher-order alcohols, however, were shown to undergo a partial oxidation pathway in the absence of gaseous O2 that is hypothesized to originate from enhanced binding to Cu sites. The decomposition of the chemical warfare agent simulant dimethyl chlorophosphate was also investigated. A hydrolysis pathway to form the significantly less toxic molecule CH3Cl was observed, highlighting the unique promotional effects and chemistry on Cu/TiO2 aerogels. The results presented exemplify both the influence of electronic metal-support interactions on catalysis and the versatile reactivity of Cu/TiO2 aerogels. / Doctor of Philosophy / Interactions between small gaseous molecules and material surfaces have very important implications for applications regarding the environment, industry, and military/public safety. The mechanisms in which gases interact with a solid surface can determine how the material can be functionally used as catalysts. Scientists and engineers start to build a fundamental understanding of what makes a catalyst successful for different applications by understanding the location and strength of interactions. A catalyst's surface acts to lower activation barriers and provide low-energy pathways for interacting molecules to chemically change, by breaking bonds for molecular decomposition and/or forming new bonds. The vibrations of chemical bonds that break and form on surfaces are probed with infrared spectroscopy at the gas-surface interface to study molecular adsorption and reactivity. In addition, a flow cell reactor is used to characterize reaction progress and identify products in real-time. A class of reactive nanoparticulate materials is utilized as a model system on which to study various chemical reactions for important applications including small molecule oxidation for industrial detoxification and clean energy applications, as well as the decomposition of chemical warfare agents. Reaction mechanisms for the oxidation of carbon monoxide and alcohols were elucidated through the utilization of the methods described above. In addition, the decomposition of a chemical warfare agent simulant is characterized. The discoveries and understanding of important chemical properties presented in this dissertation will aid in the synthesis of effective next-generation catalyst materials.

Made available in DSpace on 2016-08-19T12:56:38Z (GMT). No. of bitstreams: 1 Jaldyr de Jesus.pdf: 960775 bytes, checksum: 15b1d54e03bab9da8818d65bfa95a1e8 (MD5) Previous issue date: 2006-07-14 / This work presents oxygem reduction reaction (ORR) studies on platinum (Pt/C) and platinum-chromium alloys containing 50% (PtCr/C) or 70% in chromium (Pt3Cr) dispersed on high surface area, in acid aqueous solutions with and without metanol, with cyclic voltammetry, chronoamperometry and rotating disk electrode techniques. Electrochemical measurements have been also performed in a direct methanol unit fuel cell. The electrocatalysts were characterized by energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analyses. The ORR studies in absence of methanol in solution showed that chromium adittion does not change the reaction mechanism observed on the Pt/C and the electrocatalytic activity increases in the order PtCr/C < Pt/C < Pt3Cr/C. Such increase was attributed to a favourable interatomic distance for O2 dissociative adsorption. The alloys showed higher tolerance to methanol presence in solution than Pt, mainly the PtCr electrode due to smaller amount of active sites to methanol adsorption with respect to Pt. In solutions containing low concentration of methanol, the ORR mechanism was not affected by methanol presence. The polarization curves recorded with the unit cell showed that na increase in temperature results in an increase in the electrocatalitic activity of the anode, as well as na increase in methanol diffusion through the Nafion® membrane with consequent cathode depolarization. Furthermore, the system containing Pt3Cr/C as cathodic electrode material presented the best electrochemical performance, with power densities of ~ 55 mW cm-2, in contrast to ~ 40 mW cm-2 for the unit cell with Pt/C cathode and ~ 20 mW cm-2 with PtCr/C. / This work presents oxygem reduction reaction (ORR) studies on platinum (Pt/C) and platinum-chromium alloys containing 50% (PtCr/C) or 70% in chromium (Pt3Cr) dispersed on high surface area, in acid aqueous solutions with and without metanol, with cyclic voltammetry, chronoamperometry and rotating disk electrode techniques. Electrochemical measurements have been also performed in a direct methanol unit fuel cell. The electrocatalysts were characterized by energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analyses. The ORR studies in absence of methanol in solution showed that chromium adittion does not change the reaction mechanism observed on the Pt/C and the electrocatalytic activity increases in the order PtCr/C < Pt/C < Pt3Cr/C. Such increase was attributed to a favourable interatomic distance for O2 dissociative adsorption. The alloys showed higher tolerance to methanol presence in solution than Pt, mainly the PtCr electrode due to smaller amount of active sites to methanol adsorption with respect to Pt. In solutions containing low concentration of methanol, the ORR mechanism was not affected by methanol presence. The polarization curves recorded with the unit cell showed that na increase in temperature results in an increase in the electrocatalitic activity of the anode, as well as na increase in methanol diffusion through the Nafion® membrane with consequent cathode depolarization. Furthermore, the system containing Pt3Cr/C as cathodic electrode material presented the best electrochemical performance, with power densities of ~ 55 mW cm-2, in contrast to ~ 40 mW cm-2 for the unit cell with Pt/C cathode and ~ 20 mW cm-2 with PtCr/C.

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.

In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.

<p>In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.</p>

<p>In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.</p>

In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.

Philosophiae Doctor - PhD / In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation. / South Africa