Despite the history of studies on methanol formation from CO2, the dominant elementary reaction steps that constitute the chemical mechanism for this catalyzed process are not determined. Two main... Show moreDespite the history of studies on methanol formation from CO2, the dominant elementary reaction steps that constitute the chemical mechanism for this catalyzed process are not determined. Two main issues may cause doubt about the current level of understanding: 1) the very large difference in the coverage-dependent sticking probabilities for CO2 and CO and unavoidable CO contamination 2) the complex oxidation of the copper surface and unavoidable build-up of a (partial) oxide layer.In this thesis, we studied the sticking probability of O2 on Cu(111) and compared results to previous experimental and theoretical results. The dissociative chemisorption of O2 on Cu(111) is a direct, activated process with a minimum barrier of approximately 100 meV.In an attempt to develop a method that may undeniably quantify the reactivity of CO2 onto clean and H-containing Cu surfaces, we investigated co-adsorbed CO and O on Cu(111) and Cu(211) with RAIRS. Cu(211) oxidizes much more readily than Cu(111). For incomplete oxidation, the system CO adsorbs to small isolated metallic Cu edges and patches. Fully oxidized Cu(211) binds CO but in a rather different form than clean metallic Cu. The vibrational frequency of adsorbed CO is changed as the co-adsorbed O coverage varies on Cu(211). Show less
In the last decade, the redox interconversion between metal thiolate and disulfide compounds has been extensively investigated for copper, but not for other transition metal ions. In this... Show moreIn the last decade, the redox interconversion between metal thiolate and disulfide compounds has been extensively investigated for copper, but not for other transition metal ions. In this thesis, our investigations are described of the possibility to extend the metal thiolate/disulfide redox interconversion reactions to cobalt or iron compounds. A number of cobalt(II) disulfide and cobalt(III) thiolate compounds of different ligands and different anions are reported in this thesis. It was revealed that the anion of cobalt(II) salts, the structure of disulfide ligands, and the type of solvent influence the formation of either cobalt(II) disulfide or cobalt(III) thiolate compounds. However, a consistent trend cannot be provided to predict which of the species is generated. An important conclusion of this work is that the cobalt(II) disulfide to cobalt(III) thiolate interconversion reaction might be related to the ligand field strength of the ligand, and the binding strength and ligand field strength of the anions and solvent used. Apart from the cobalt compounds, two iron(II) disulfide compounds were reported in this thesis as well. However, so far we were not able to trigger the conversion of these compounds to their respective iron(III) thiolate compounds. Show less
Hydrogen peroxide (H2O2) is produced following injury and is required for regeneration. However, how H2O2 coordinates multiple signalling pathways required for regeneration is not known. Protein... Show moreHydrogen peroxide (H2O2) is produced following injury and is required for regeneration. However, how H2O2 coordinates multiple signalling pathways required for regeneration is not known. Protein-tyrosine phosphatases (PTPs) are regulators of signal transduction, reversing the phosphorylation of substrates, and are essential for many cellular processes. PTPs are also highly sensitive to reversible oxidation-mediated inhibition by H2O2.My research identified that some, but not all, PTPs become oxidized following amputation of the zebrafish caudal fin, and implicates PTPs that are oxidized as necessary for the regenerative process. Furthermore, I delineated that the PTPs Shp2 and Pten are required for the regenerative outgrowth phase of regeneration, and that Shp2 and Pten have a role in driving MAPK signalling and balancing PI3K signalling, respectively, during this phase. 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
Common alkyd paint will not have dried within two hours without drying catalysts. The drying catalyst (also called __drier__) that is generally used is based on the heavy metal cobalt. Since cobalt... Show moreCommon alkyd paint will not have dried within two hours without drying catalysts. The drying catalyst (also called __drier__) that is generally used is based on the heavy metal cobalt. Since cobalt salts are suspected to be carcinogenic, it is of the utmost importance that alternative driers are found and that cobalt can be replaced as a drier in alkyd paint. In this thesis newly developed manganese compounds are presented which show a comparable or better drying activity than existing cobalt driers. These manganese driers are thus potential replacements for the toxic cobalt compounds. Results pertaining to the mechanism of action of the new manganese driers are also discussed. These results will make the future development of alkyd paint driers easier. Huis-tuin-en-keuken alkydverf is uit zichzelf niet binnen twee uur droog. Daarom worden drogingsversnellers (katalysatoren) aan de verf toegevoegd, om het drogingsproces te versnellen. De meest gebruikte drogingskatalysator (ook wel __droger__ genoemd) in alkydverf is gebaseerd op het zware metaal kobalt. Aangezien kobalt vermeend carcinogeen is, is het noodzaak om alternatieve drogers te vinden zodat kobalt vervangen kan worden. In dit proefschrift worden (nieuw ontwikkelde) mangaanverbindingen gepresenteerd die dezelfde of soms zelfs een betere drogingsactiviteit vertonen als de bestaande kobaltdroger en dus als mogelijke vervanger aangemerkt kunnen worden. Ook worden resultaten gepresenteerd mbt de precieze werking van de mangaandrogers, zodat het in de toekomst makkelijker zal zijn nieuwe drogers te ontwikkelen voor bijvoorbeeld een specifieke verfformulering. Show less
