Hydrogen fuel cells are expected to be pivotal in the energetic transition towards renewable energy sources such as solar and wind power. However, their industrial scalability is severely hindered... Show moreHydrogen fuel cells are expected to be pivotal in the energetic transition towards renewable energy sources such as solar and wind power. However, their industrial scalability is severely hindered by the high cost and degradation rate of platinum catalysts, one of their key components. Addressing this challenge necessitates developing better catalysts, which requires a better fundamental understanding of their reactivity and degradation mechanism. In this thesis, we investigate the (in)stability of model platinum surfaces submerged in liquid and under applied voltage, thus simulating the operational conditions of fuel cells. For this we use a home-build Electrochemical Scanning Tunneling Microscope (EC-STM), which allows us to observe, in real time, the surface structure at the atomic scale. Our findings elucidate the origin of the platinum surface roughening that takes place upon voltage cycling. Moreover, we demonstrate that closely-spaced atomic steps are prone to bunch together, resulting in steps with multi-atomic height. This structural change has a significant effect on the catalyst reactivity, as we explain in detail. Overall, this dissertation contributes to a deeper fundamental understanding of the surface processes that drive platinum surface restructuring as well as their implications for reactivity. Show less
The research presented in this thesis explores the chemotherapeutic potential of metal-based compounds as chemotherapy agents, with an initial focus on the synthesis and DNA interaction studies of... Show moreThe research presented in this thesis explores the chemotherapeutic potential of metal-based compounds as chemotherapy agents, with an initial focus on the synthesis and DNA interaction studies of platinum and palladium compounds utilizing the [Pt(bapbpy)]2+ scaffold. The study identifies intercalation as the primary mechanism of action for these complexes. Furthermore, it provides a detailed structure-activity relationship analysis, highlighting the critical role of the complex's protonation state in influencing its biological activity and efficacy. Subsequently, the study delves into photoactivated chemotherapy (PACT) using ruthenium (II) complexes, where light activation of ruthenium complexes enables targeted drug delivery to tumor cells, thereby reducing adverse effects. This research emphasizes the development of ruthenium-based compounds that can photorelease a DNA repair inhibitor, specifically targeting the RAD51 protein, essential for Homologous Recombination (HR). By disrupting the DNA repair mechanisms in cancer cells, this approach seeks to enhance the cytotoxicity of the therapy and address drug resistance. Show less
Heterogeneous catalysis is essential to many industrial applications. These catalysts are often comprised of supported nanoparticles, which contain various different surface sites. For some... Show moreHeterogeneous catalysis is essential to many industrial applications. These catalysts are often comprised of supported nanoparticles, which contain various different surface sites. For some reactions, the presence of specific surface sights dominates the overall reactivity. Fundamental insight into the influence of different surface sites on the surface reaction dynamics may lead to better catalyst design in the future. In this thesis, we combine ultra-high vacuum techniques and (curved) single crystal surfaces to study surface structure effects relevant to heterogeneous catalysis. We study how step edges on a platinum surface affect (elementary) reactions that occur in oxygen reduction: hydrogen dissociation, hydrogen recombination, and oxygen reduction. Show less
In most applications, electrocatalysts exhibit a large surface area to volume ratio, for example using nanoparticles. To fully understand fundamental electrochemical processes at the length scale... Show moreIn most applications, electrocatalysts exhibit a large surface area to volume ratio, for example using nanoparticles. To fully understand fundamental electrochemical processes at the length scale of these nanoparticles, it is necessary to use specialized experimental techniques. In this thesis, the stability and activity of platinum electrode surfaces are studied at the nano- and micrometer scale using Electrochemical Scanning Probe Microscopy (EC-SPM) techniques. Chapters 2 and 3 describe the roughening of an atomically flat Pt(111) surface upon repetitive oxidation and reduction. These data were acquired using a combination of Electrochemical Scanning Tunneling Microscopy (EC-STM) and Cyclic Voltammetry (CV). Chapter 4 describes the development of a new technique to resolve small differences in local reactivity: voltammetric Scanning Electrochemical Cell Microscopy (SECCM). The power of this technique is demonstrated by studying the reactivity of a polycrystalline Pt sample towards hydrazine oxidation. Finally, Chapter 5 compares the reactivity of small Pt ultramicroelectrodes to that of conventional macroelectrodes. Show less
The field of transition-metal based chemotherapeutics are dominated by derivatives of cisplatin, but a major downside of these platinum based chemotherapeutics is their lack of selectivity... Show moreThe field of transition-metal based chemotherapeutics are dominated by derivatives of cisplatin, but a major downside of these platinum based chemotherapeutics is their lack of selectivity that leads to undesirable side effects. In this work we present alternative strategies such as light-activation with different transition-metals such as ruthenium and palladium that have the potential to be more selective than cisplatin type of drugs. Show less
Today, the energy sector is highly dependent on heterogeneous catalysis because a future solution to end our dependency on natural sources lies in generating hydrogen by splitting water. Several... Show moreToday, the energy sector is highly dependent on heterogeneous catalysis because a future solution to end our dependency on natural sources lies in generating hydrogen by splitting water. Several transition metals, such as Pt, are known to be good catalyst materials for water splitting reactions. They play a key role in understanding the fundamental aspects of the elementary interactions occurring on the surfaces of catalysts. These surfaces, however, are generally very complex and contain a wide distribution of structurally and chemically different sites with different activities. One of the key issues in optimizing the activity of the catalysts is to distinguish and specify the active sites on the surface. In this thesis we use highly corrugated Pt surfaces and UHV techniques (TPD, LEED, and STM) to explore the effects of surface defects on adsorption and desorption of water and related adsorbates. We elucidate to what extent the substrate type influences the structure of interfacial water both in the monolayer and thin film regime. Our studies also show that step geometry is the determining factor in low temperature oxygen dissociation. Show less
Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean... Show more Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean fuels and needed for the abatement of exhaust gases. Frequently, the employed catalysts are being discovered in a very empirical way; by trial and error. However, designing catalysts based on detailed understanding is preferred. Obtaining understanding is very difficult, because catalysts are very complex materials. Furthermore, its properties often depend on the atmosphere surrounding the catalysts, i.e., the temperature and pressure of reactants and products, which they are exposed to, and these properties also change over time. The major part of this thesis focuses on structural changes of Pt model catalysts exposed to high oxygen pressures at elevated temperatures. The changes were measured with a ReactorSTM, a special version of a scanning tunneling microscope (STM) adapted to operate at high pressure and temperatures. These observations show that various surface oxide with a single-layer thickness form under reaction conditions. These oxides are structurally and chemically different from the Pt bulk oxides. The second part describes a set of experiments to understand the role of low-coordinated atoms and water in Au-catalyzed CO oxidation. Show less
Heterogeneous catalysis is very important for industrial applications and the environment. It is known that precious metals, such as Pd and Pt, can be good catalyst materials for various reactions.... Show moreHeterogeneous catalysis is very important for industrial applications and the environment. It is known that precious metals, such as Pd and Pt, can be good catalyst materials for various reactions. However, these metals are expensive and their catalytic action is not yet completely understood. In the search for better and cheaper materials, more fundamental knowledge is necessary. We use ultra-high vacuum techniques and well-ordered Pd and Pt single crystals to further investigate the oxygen dissociation process and the interaction of water with deuterated surfaces. Show less
In this thesis two subjects are treated. The first one is the poisoning of hydrogen dissociation on Pt(533) by CO. It was found that decorating the step edges of Pt(533) by CO does not only block... Show moreIn this thesis two subjects are treated. The first one is the poisoning of hydrogen dissociation on Pt(533) by CO. It was found that decorating the step edges of Pt(533) by CO does not only block the indirect dissociation mechanism and the direct dissociation at step edges but also introduces an additional barrier for dissociation at the terraces. The second area contains a description of how a cylindrical Ni single crystal is employed in dissociation dynamics measurements. The analysis of the circumference by LEED is explained. Results for hydrogen dissociation are shown. They are analyzed by means of a model introduced for hydrogen dissociation on stepped Pt surfaces with (111) terraces and (100) steps. Show less
Nitrate reduction on Sn-modified polycrystalline Pt has been investigated. NO is the main product at high Sn coverage, whereas N2O is dominant at low Sn coverage. The N2O reduction on Sn-modified... Show moreNitrate reduction on Sn-modified polycrystalline Pt has been investigated. NO is the main product at high Sn coverage, whereas N2O is dominant at low Sn coverage. The N2O reduction on Sn-modified Pt electrodes indicates electrochemical formation of N2 is related to pristine Pt sites. Moreover, homogeneous chemical reactions of intermediates products also contribute to N2O and N2 formation of in solution. The p-block metals have been studied: Cd, In and Sn show a promoting effect; Ga shows a limited enhancement; Tl shows a special promoting effect in sulfuric acid; Pb shows a weak formation of N2O. Density Functional Theory calculations show that Sn and In enhance nitrate adsorption compared with pristine Pt. Moreover, ammonia is found as the only product on Pt. After modification by Sn, hydroxylamine is specifically found with nitrite, which supports that nitrate reduction to nitrite is enhanced by Sn and Sn could steer the hydrogenation of NOads. However, solution pH is an important factor. On Pt, nitrate reduction is only observed in acidic solution. On Rh, a higher activity is observed in wide pH, which suggests a mechanism that HNO3 molecule is the active species. However, Rh additionally shows a special ability to reduce NO3- directly. Show less
This project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater... Show moreThis project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater remediation; electrochemistry strives to achieve selectivity to harmless products (N2). A multi-pronged approach has been followed, aimed at establishing the influence of several variables (electrocatalyst material, surface structure, pH and electrode potential) on the catalytic activity and the product distribution, which has been determined with in situ analytical techniques (mass spectrometry and infrared spectroscopy). The molecular underpinnings of nitrite reduction have thereby been unravelled for transition metals, showing that an optimal catalytic performance is achieved when metals intermediate affinities to reaction intermediates (Sabatier Principle). The all-important concept of structure sensitivity also applies to nitrite reduction at Pt electrodes, although only in alkaline media: a Pt(100) single-crystal is the sole Pt surface able to achieve the desired direct conversion of nitrite into 100% N2. Such selectivity is unparalleled for a simple monometallic surface and is an outstanding finding. Additionally, the nitrite-reducing performance of bio-inspired catalysts, (electroactive metalloporphyrins) was investigated. A further side-project of this PhD thesis has also been the electrochemical characterization of preferentially-oriented cuboid Pt nanoparticles synthesized with the innovative __cathodic corrosion__. Show less
This thesis describes the construction of a second generation high-pressure, high-temperature scanning tunneling microscope, the ReactorSTM, with which the surfaces of catalysts can be studied... Show moreThis thesis describes the construction of a second generation high-pressure, high-temperature scanning tunneling microscope, the ReactorSTM, with which the surfaces of catalysts can be studied under relevant reaction conditions. Furthermore, the thesis describes three separate catalytic systems at ~ 1 bar, and elevated temperatures. Firstly, NO reduction on Pt(100), in which a mathematical model for the reaction mechanism, following Langmuir-Hinshelwood kinetics, is proposed. Secondly, CO oxidation, in which the Pt(110) surface is atomically resolved at high p, T. Thirdly, the thesis describes a successful pilot experiment about the hydrodesulphurization of thiophene, which is catalytically activated by molybdenum disulphide nano-crystallites on an Au(111) support. Show less
We have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those... Show moreWe have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those sites. Under UHV conditions OH groups can be formed on Pt(111) by pre-covering the surface with O adatoms, causing water to dissociate. We have shown that on stepped platinum surfaces OHad might not be as readily formed as one would assume based on the energetics of OH adsorption alone. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on D/Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on D/Pt(553). Under electrochemical conditions we show that in spite of the similar looking cyclic voltammograms, the kinetics of underpotential deposited hydrogen are significantly different in acidic and alkaline media. In alkaline media the ad- and desorption process is slow, whereas it is very fast in acidic media. We have pointed out three discrepancies in the current interpretation of the blank cyclic voltammetry of stepped platinum surfaces and propose a co-adsorption model that accounts for these discrepancies. Show less
This thesis aimed at preparing and characterizing two different model catalysts after their exposure at different temperatures to oxygen, carbon monoxide and hydrogen. The experiments were... Show moreThis thesis aimed at preparing and characterizing two different model catalysts after their exposure at different temperatures to oxygen, carbon monoxide and hydrogen. The experiments were performed in an ultra-high vacuum (UHV) set-up using a range of techniques including scanning tunneling and atomic force microscopy. The first part of the thesis deals with platinum deposited onto highly oriented pyrolytic graphite (HOPG). It was found that a sub-monolayer of the deposited metal on this substrate forms randomly distributed two-/three-dimensional particles. Analysis of the morphology and height distribution of Pt particles on the HOPG(0001) surface after annealing in UHV and in the presence of low pressures of oxygen, carbon monoxide and hydrogen indicates that their growth proceeds via coalescence. The second part of the thesis is devoted to the preparation of model manganese oxide surfaces starting with the MnO(100) surface, which were used as a support for Pt deposits. The preparation of manganese oxide surfaces was based on annealing of MnO(100) single-crystals at different temperatures in UHV and in the presence of argon, oxygen and hydrogen. The first results of Pt deposition on the MnO(100) surface and on this surface altered by annealing in the presence of oxygen and hydrogen are described. Show less
The thesis project is devoted to the __search of antineoplastic ruthenium/platinum/copper complexes containing also intercalator ligands; such intercalators may show efficient DNA-cleaving and DNA... Show moreThe thesis project is devoted to the __search of antineoplastic ruthenium/platinum/copper complexes containing also intercalator ligands; such intercalators may show efficient DNA-cleaving and DNA-binding properties__. The studies have been carried out using a variety of techniques. Study of the in vitro cytotoxicity against human tumour cell lines along with cellular uptake has been the pivotal point of this research. Synthetic methodologies of the new complexes have been designed to establish structure-activity relation in several series of related complexes. Platinum complexes of derivatized-phenanthroline, pyridine and pyrimidine, have been synthesized and studied in detail for their biological activity. These complexes are different in structure and in overall charges, and were studied to elucidate the effects on the activity profile. A self-activating copper-complex formed from a unique amino-phenol ligand (Hpyramol) inspired the synthesis of platinum and ruthenium analogues. Biological studies including cellular uptake, conformational changes (CD and UV) and DNA cleavage have been performed to interpret the changes in activity profile upon various metal additions. Ruthenium complexes are known as suitable candidates for anticancer (specially as antimetastatic drugs) agents. A group of ruthenium(III) complexes has been studied for their anticancer activity and their DNA-binding properties. The extensive area of homo- or heterometallic dinuclear compounds opens up an interesting challenge towards the synthesis of complexes. The studies of different combinations viz., Ru-Ru, Cu-Cu and Pt-Pt, have been performed to design new series of anticancer complexes. Show less
The main theme of this thesis is the catalytic oxidation of CO, which we have investigated on several model catalyst surfaces at atmospheric pressures and elevated temperatures with the combination... Show moreThe main theme of this thesis is the catalytic oxidation of CO, which we have investigated on several model catalyst surfaces at atmospheric pressures and elevated temperatures with the combination of Scanning Tunneling Microscopy and Mass Spectrometry.The study of CO oxidation on low-index and vicinal palladium surfaces has shown that when exposed to ambient pressures of oxygen at elevated temperature, these surfaces oxidize irrespective of their orientation. In this pressure regime the oxides were shown to have a higher reactivity than the metallic surfaces.In a certain window of partial pressure combinations of O2 and CO reaction rate oscillations were observed on Pd(100) and on its vicinal surface Pd(1.1.17). ). CO adsorption on Pt(111) was found to lead to the formation of a regular overlayer structure, identified as (√19 x √19) R23.4°-13CO. The stability of this structure under different reaction conditions was discussed. These results were further used to illustrate the importance of temperature in a catalytic system.Spectacularly high conversion rates could be achieved during CO oxidation at atmospheric pressure on metallic Pt(100) surface. Show less
The research described in this Ph.D. Thesis has been devoted to the design and development of polynuclear polypyridyl ruthenium and ruthenium-platinum complexes in search of new anticancer agents.... Show moreThe research described in this Ph.D. Thesis has been devoted to the design and development of polynuclear polypyridyl ruthenium and ruthenium-platinum complexes in search of new anticancer agents. A variety of polynuclear ruthenium and ruthenium-platinum complexes has been synthesized with a long and flexible linker. The complexes are characterized and have been studied for anticancer activity. The ruthenium unit of the dinuclear complexes varies in molecular structure, which may result in different interactions with DNA, the target of anticancer platinum and ruthenium antitumor compounds. The monofunctional ruthenium unit coordinates to the DNA-model base 9-ethylguanine. Variable temperature 1H NMR experiments prove that the base is hindered in its free rotation at room temperature. The crystal structure of a dinuclear ruthenium-platinum complex shows that the platinum unit is capable of intercalation and coordination (in)to DNA. Trinuclear and tetranuclear ruthenium and ruthenium-platinum complexes show higher activity than the dinuclear derivatives. A tetranuclear ruthenium complex displays interesting biological features. Human ovarian cisplatin sensitive carcinoma cells adhere together and form clots upon incubation of the complex. The effect possibly indicates antimetastatic activity. Dinuclear and trinuclear ruthenium-platinum complexes of short and semi-rigid linkers do not show significant activity against different cancer cell lines. Show less
This thesis describes a variety of asymmetric cis- and trans-platinum(II) complexes. The major aim of this research has been the design of complexes with high antitumor activity that may overcome... Show moreThis thesis describes a variety of asymmetric cis- and trans-platinum(II) complexes. The major aim of this research has been the design of complexes with high antitumor activity that may overcome cisplatin resistance, and to establish a comparison between complexes with both geometries. These new type of asymmetric platinum complexes contain in all cases the iPram ligand and in addition either aliphatic amines or azole ligands. Furthermore, a strong emphasis on asymmetric trans-Pt(II) complexes with azole ligands is presented in this research. Show less
Inspired by cisplatin, the inorganic drug discovered by Barnett Rosenberg in 1965, the research described in this thesis uses targeting ligands, or ligands varied in a combinatorial fashion, to... Show moreInspired by cisplatin, the inorganic drug discovered by Barnett Rosenberg in 1965, the research described in this thesis uses targeting ligands, or ligands varied in a combinatorial fashion, to find platinum complexes with more specific modes of action. These studies have lead to the development of novel (solid-phase) synthetic methods and to the discovery of several compounds with promising biological properties. Show less
Surfaces play an important role in chemical reactions: the metal surface in the car exhaust catalyst reduces the amount of harmful species. In the interstellar medium and the earth's stratosphere,... Show moreSurfaces play an important role in chemical reactions: the metal surface in the car exhaust catalyst reduces the amount of harmful species. In the interstellar medium and the earth's stratosphere, ice surfaces play an important role both by the formation of molecules and by the destruction of ozone in the atmosphere. To understand reactions on a surface it is essential to know the structure of the surface and the interaction of the surface with adsorbed species. The first part of this thesis describes a study of the surface of an ice film. The surface of the film can change before the bulk of the ice film changes. This surface structure - chaotic or ordered - determines the reactivity of the surface and has therefore important consequences for reactions in the interstellar medium and the earth's stratosphere. To better understand the interaction between the surface and the adsorbed particles the energy transfer between these two has been studied. As described in the second part of this thesis, this energy transfer depends strongly on how and where the molecules are adsorbed on the surface - on atomic length scale. This fundamental study is possibly relevant for the development of new chemical processes, in which the use of sunlight plays an important role and for the further development of the car exhaust catalyst. Show less
