In surface science there is great effort to move from studying simple, flat model surfaces in vacuum to investigating more complex model catalysts in gas environments (in situ). This thesis gives... Show moreIn surface science there is great effort to move from studying simple, flat model surfaces in vacuum to investigating more complex model catalysts in gas environments (in situ). This thesis gives three examples of such studies using microscopy and spectroscopy.Exposure of ZnO(10-10) to moderate pressures of water in an in situ scanning tunneling microscope reveals that the surface roughens. The flat ZnO(10-10) is thus only conditionally suited as a model catalyst for reactions involving water.In the same microscope, surface gold oxide formation is observed on TiO2/Au(111) during CO oxidation at 1 bar pressure. Comparisons to the Au(111) surface suggest that the titania does not supply atomic oxygen to the Au(111) substrate as part of the reaction mechanism of the CO oxidation.Co(0001) is investigated as a model catalyst for Fischer-Tropsch synthesis, the reaction of CO and H2 to form hydrocarbons. In this thesis the oxidation behavior of the cobalt and the adsorption of carbon species during the reaction are investigated using near-ambient pressure X-ray photoelectron spectroscopy.Generally, this thesis exemplifies the significant influence that small concentrations of contaminants in gases and materials can have on the structure and behavior of surfaces in in situ studies. Show less
Claes, L.M.G.F.E.; Groot, T. de; Huisman, H.; Kort, J.W. de; Os, B. van 2021
Since 2011, the Faculty of Social Sciences (FSW) and the Institute of Environmental Sciences (CML) of Leiden University, in cooperation with Isabela State University and the Mabuwaya Foundation in... Show moreSince 2011, the Faculty of Social Sciences (FSW) and the Institute of Environmental Sciences (CML) of Leiden University, in cooperation with Isabela State University and the Mabuwaya Foundation in the Philippines organize an annual month–long international, interdisciplinary course on sustainable development, water issues and water management in the Cagayan River basin in Northeast Luzon in the Philippines. Thirty students participate in this course, 15 through Leiden University and 15 through Isabela State University. The students are enrolled in different studies, encompassing social, natural and applied sciences. The annual report contains background information, all student reports and the online blog that the students maintained during the course. 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
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
The thesis "Light-induced molecular processes on ice" deals with two main issues: first, the interaction of water with a platinum surface, under very well-defined conditions (at liquid nitrogen... Show moreThe thesis "Light-induced molecular processes on ice" deals with two main issues: first, the interaction of water with a platinum surface, under very well-defined conditions (at liquid nitrogen temperature in a very low-pressure environment (Ultra-High Vacuum: pressure 2 x 10-11 mbar)), and second, the photochemistry of small, naturally occurring, organic molecules such as bromoform (CHBr3) molecules on ice surfaces. The first topic is of relevance for electrochemistry, where water-metal interactions are crucial in determining the system's reactivity. The second topic is relevant for our understanding of processes encountered in the Earth's atmosphere. In particular, for atmospheric chemistry, the fundamental steps of the photochemical reaction of bromoform on ice surfaces induced by UV light, are elucidated. This reaction constitutes an important step in the ozone depletion cycle, which greatly affects our atmosphere. Photodissociation studies reveal a rich UV-induced photochemistry of bromoform on ice: various direct fragmentation pathways, as well as formation of new, ice-mediated C—C and C—O bond containing chemical species. Given the previously reported detection of bromoform in the stratosphere, these observations may have significant implications for current models describing stratospheric ozone depletion. Show less
