Curved single crystals provide variable, but well-defined surface structures. These curved surfaces have enormous potential for applications in surface chemistry, e.g. to unravel the role of... Show moreCurved single crystals provide variable, but well-defined surface structures. These curved surfaces have enormous potential for applications in surface chemistry, e.g. to unravel the role of specific sites in the reaction mechanism. Measurements can be repeated on the same crystal with incremental changes of the surface structure. Because effectsof sample heterogeneity are avoided, curved crystals make it possible to detect even subtle differences in surface reactivities and assign them to specific surface sites. They were used throughout this thesis to study the effects of surface structure onelemental chemical reaction steps, such as hydrogen dissociation and recombination, or water desorption. 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
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
