Heterogeneous catalysis is one of the fundamental processes of modern life, being common in industrial refinery and hydrogen vehicles, all the way to the living cell. The dissociation of H2 on Cu... Show moreHeterogeneous catalysis is one of the fundamental processes of modern life, being common in industrial refinery and hydrogen vehicles, all the way to the living cell. The dissociation of H2 on Cu(111) is an important benchmark system for studying heterogeneous catalysis, with a large and varied amount of experimental and theoretical data available.In this thesis I present my recent advances in including the effects of surface temperature on the H2/Cu(111) reaction in not only classical dynamics, but also quantum dynamics. I show how we can include surface temperature effects by treating the surface as static, but distorted, and present how the neglect of energy exchange between the surface and the hydrogen molecule does not appear to affect the dissociation or (ro)vibrationally elastic scattering probabilities of the H2 molecule. Furthermore, I show how treating the hydrogen at a quantum dynamical level has some minor effects on the scattering probabilities when compared to classical dynamics, but in general agrees very well. Finally, I also discuss how including the surface temperature effects improves agreement with the experimentally obtained dissociation curves, but also how smaller features of the experimental results are not reproduced by our models. Show less
Heterogeneous catalyzed processes are highly significant to the chemical industry. Dissociative chemisorption (DC) of molecules on surfaces is always considered as a step with a high degree of rate... Show moreHeterogeneous catalyzed processes are highly significant to the chemical industry. Dissociative chemisorption (DC) of molecules on surfaces is always considered as a step with a high degree of rate control for heterogeneous catalysis. Our ability to comprehend the different mechanisms underlying DC on metal surfaces could benefit significantly from the availability of an accurate database for the barrier heights of elementary molecule-metal surface reactions. In this work, we used a recent implementation of specific reaction parameter (SRP) to density-functional theory (DFT) (SRP-DFT) to develop potential energy surfaces (PESs) for molecule-surface reactions. The PESs were used for molecular beam simulations and compared with molecular beam experiments. The barrier heights extracted from these PESs are now used for benchmarking. Show less
In this thesis, we consider various (electro)chemical phenomena at surfaces and nanoparticles and their underlying atomistic processes, which we studied using first-principles methods such as... Show moreIn this thesis, we consider various (electro)chemical phenomena at surfaces and nanoparticles and their underlying atomistic processes, which we studied using first-principles methods such as density functional theory. These phenomena range from CO2 reduction to C2 and C3 species, through solvation of adsorbates on various surface features of late transition metals, to the impact of graphene on hydrogen evolution reaction, cathodic corrosion and surface oxidation of Pt. With our thermodynamic and kinetic calculations, we provide explanations for experimental observations by unraveling underlying phenomena, support novel computational methods and techniques, and propose new atomic structures that explain prior findings and provide inroads into future electrocatalytic research. Show less
Metals surfaces form a group of effective catalysts for the reaction of small molecules such as hydrogen (H2). In order to improve the predictive power of theory with respect to the catalytic... Show moreMetals surfaces form a group of effective catalysts for the reaction of small molecules such as hydrogen (H2). In order to improve the predictive power of theory with respect to the catalytic activity of small molecules reacting at metal surfaces, the way in which metal surfaces modify the potential energy of molecules needs to be understood at a fundamental level. Currently density functional theory (DFT) is the only electronic structure method that is accurate enough to achieve chemical accuracy while being cheap enough to make large comparative studies feasible. The work in this thesis is concerned with the creation of highly accurate density functionals that can give a simultaneously good description of the metal surface, the molecule, and the molecule interacting with the metal surface, as well as the description and simulation of supersonic molecular beam experiments and associative desorption experiments needed to validate the obtained results. Show less
This research was about to better understanding of heterogeneous catalyzed processes which would help to design better and more efficient catalysts but it is hard to achieve because of their high... Show moreThis research was about to better understanding of heterogeneous catalyzed processes which would help to design better and more efficient catalysts but it is hard to achieve because of their high level of complexity. In this way, we compared molecular beam experiments with molecular dynamics simulations to improve over the theoretical method used, called density functional theory (DFT), to achieve chemical accuracy (i.e., errors smaller than 1 kcal/mol) for the reaction studied. Show less
A catalyst is a compound that speeds up a chemical reaction without being consumed itself. The proces of catalysis is one of the most important technologies in the modern world. Approximately 90%... Show moreA catalyst is a compound that speeds up a chemical reaction without being consumed itself. The proces of catalysis is one of the most important technologies in the modern world. Approximately 90% of all chemicals and materials around us is produced using catalysis. To get a better understanding of these industrial processes, it is important to investigate the exact role of the catalyst in the process, and the factors that can influence the outcome of the reaction. Therefore, it is necessary to first comprehend simple processes, such as the dissociation of hydrogen, the smallest molecule on Earth, on metal surfaces. In addition, this reaction is an elementary step in many industrial processes. My thesis describes the dissociation of hydrogen on bare and CO-precovered ruthenium, and on stepped platinum. These metals are important catalysts in e.g. ammonia synthesis (ruthenium) and fuel cells (platinum). I have discovered that ruthenium is a very good catalyst for hydrogen dissociation. The presence of CO, however, poisons the catalyst, and less hydrogen is able to dissociate. The presence of steps on a platinum surface increases the catalytic activity of the metal significantly. Show less
Sodium alanate (NaAlH4) is a prototype system for storage of hydrogen in chemical form. However, a key experimental finding, that early transition metals (TMs) like Ti, Zr, and Sc are good... Show moreSodium alanate (NaAlH4) is a prototype system for storage of hydrogen in chemical form. However, a key experimental finding, that early transition metals (TMs) like Ti, Zr, and Sc are good catalysts for hydrogen release and re-uptake, while traditional hydrogenation catalysts like Pd and Pt are poor catalysts for NaAlH4, has so far gone unexplained. We have performed density functional theory calculations at the PW91 generalised gradient approximation level on Ti, Zr, Sc, Pd, and Pt interacting with the (001) surface of nanocrystalline NaAlH4, employing a cluster model of the complex metal hydride. A key difference between Ti, Zr, and Sc on the one hand, and Pd and Pt on the other hand is that exchange of the early TM atoms with a surface Na ion, whereby Na is pushed on to the surface, is energetically preferred over surface absorption in an interstitial site, as found for Pd and Pt. The theoretical findings are consistent with a crucial feature of the TM catalyst being that it can be transported with the reaction boundary as it moves into the bulk, enabling the starting material to react away while the catalyst eats its way into the bulk, and effecting a phase separation between a Na-rich and a Al-rich phase. In addition, the role of different active species such as Ti2 and TiH2 has been studied using the same model. The results imply that Ti2 and TiH2 are more stable in the subsurface region of the cluster than on the surface. Calculations were performed on the decomposition of two calcium alanates, to determine zero-point energy corrected enthalpies of dehydrogenation for these compounds, and to determine whether destabilization of LiBH4 by CaH2 might improve the performance of this material. Show less
