This thesis systematically studies the physicochemical properties of non-planar, propeller-shaped, polycyclic aromatic hydrocarbons. The synthesis of several so-called propellerenes is described on... Show moreThis thesis systematically studies the physicochemical properties of non-planar, propeller-shaped, polycyclic aromatic hydrocarbons. The synthesis of several so-called propellerenes is described on a gram scale, using optimized procedures aimed at using less hazardous reagents and reducing the amount of organic solvent used. The conformational behavior of several propellerenes is studied experimentally using variable temperature NMR, and findings corroborated using high-level DFT computations. The origin of the conformational preference of propellerenes is elucidated using a novel adaptation of the activation-strain model. By computationally dissecting propellerenes into its constituent parts, the preference of these parts can be analyzed. The spectroscopic properties of conformationally pure propellerenes are studied experimentally, and experimental findings explained on a molecular orbital level, using time dependent DFT computations. Lastly, the supramolecular behavior of propellerenes is studied by the production of molecularly thin films, using the Langmuir-Blodgett technique. These thin films are imaged using electron microscopy, the molecular dynamics at the air-water interface studied computationally, and the physical properties of the thin films quantified using AFM nanoindentation. These propellerene-based thin films are, for the first time, found able to be free-standing over nanometer distances. Combined, this thesis establishes propeller-shaped, polycyclic aromatic hydrocarbons as an independent field of study. Show less
Catalysis is of extreme relevance in the production of everyday materials and plays a central role in many aspects of our life. On the industrial level, metal based catalysts are widely used to... Show moreCatalysis is of extreme relevance in the production of everyday materials and plays a central role in many aspects of our life. On the industrial level, metal based catalysts are widely used to produce molecular hydrogen, which can be used as fuel, or nitrogen, one of the building blocks in the fertilizers synthesis, and other fundamental molecules. A better understanding of heterogeneous catalyzed processes would help to design better and more efficient catalysts but it is hard to achieve because of their high level of complexity. Molecular dissociation on metal surfaces is usually a multi-step process which can be best investigated through a joint experimental and theoretical effort. The comparison of molecular beam experiments with molecular dynamics simulations can help to improve over the theoretical method used, called density functional theory (DFT), in order to achieve chemical accuracy (i.e., errors smaller than 1 kcal/mol) for the reaction studied. As we show in the research reported in the thesis, being able to accurately compute the dissociation barriers for methane on metals like nickel and platinum is of great importance in order to make predictions about the most reactive sites on the surface and possibly, in the future, it can help improving over industrial catalysts. Show less
In this thesis we have discussed several parameters that affect the electrochemical conversion of enviromentaly harmful molecules such as nitrates and carbon dioxide to more valuable and less... Show moreIn this thesis we have discussed several parameters that affect the electrochemical conversion of enviromentaly harmful molecules such as nitrates and carbon dioxide to more valuable and less deleterious compounds, in order to cast light onto the mechanism of the reaction to achieve an efficient and selective system.The thesis is divided in two main parts, the reduction of nitrates(chapter 2) and the mechanistic study of CO2 conversion to different products such as ethanol(chapter 3), ethylene(chapters 4 and 5) and propylene carbonate (chapter 6). Show less
In this study we focused on the simulation of the interaction of water and its dissociation products hydrogen, oxygen and OH with platinum surfaces that contain a periodic arrangement of single... Show moreIn this study we focused on the simulation of the interaction of water and its dissociation products hydrogen, oxygen and OH with platinum surfaces that contain a periodic arrangement of single-atom-high steps. We simulate these interactions using the framework of density functional theory and employ high-performance computing resources such as the Cartesius supercomputer of SURFsara. We find that the two possible types of step edges exhibit increased binding strengths compared to the flat parts of the interface. This binding strength is a key factor in the chemical reactivity of these surfaces. Furthermore, we investigate the structure of higher coverages of water molecules around the step edges, where we observe surprising changes, namely the appearance of four, five and seven-membered rings, compared to the six-membered rings that are usually observed on the flat surfaces. Our predictions for these structures are confirmed using high-resolution scanning tunneling microscopy data. Our results are among the first simulations of high-coverage water adsorption on regularly stepped platinum surfaces, which will help advance our understanding of solvation effects at the step edges, which are relevant for the fields of solvation science, electrochemistry and surface science. Show less
What is the catalytic role played by titanium in the hydrogen storage material NaAlH4? This thesis aims at unraveling the dynamics of an elementary reaction: H2 dissociation on Ti/Al(100) surfaces.... Show moreWhat is the catalytic role played by titanium in the hydrogen storage material NaAlH4? This thesis aims at unraveling the dynamics of an elementary reaction: H2 dissociation on Ti/Al(100) surfaces. Although this reaction is not the rate limiting step in the hydrogen storage of NaAlH4, it is an important reaction to produce atomic hydrogen for the other reaction steps. To achieve the stated goal, we test a large set of possible slab models to represent the Ti/Al(100) surface. After considering the stability of the slab model itself and the barrier height for H2 dissociation, we carefully select two possible slab models: (1) the 1/2 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface with Ti atoms in the second layer, (2) the 1 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface with Ti atoms in the first and third layers. Using these two slab models, potential energy surfaces (PES) are calculated. The H2 dissociation probabilities and rate constants are then calculated. The results suggest that the 1 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface may be the most realistic model for H2 dissociation on Ti/Al(100) surfaces relevant for the hydrogen storage material NaAlH4. In this thesis, time-dependent wave packet, quasi-classical and classical dynamics, and transition state theory have been imployed to calculate the micro-canonical reaction probabilities and canonical reaction rate constants. Show less
