Um die Korrelation zwischen Partikelgröße und Reaktivität von Pd Nanopartikeln auf Eisenoxid zu untersuchen wurde die experimentelle Methode Einkristalladsorptionskalorimetrie mit der Präparation von Modellsystemen kombiniert. Da diese Systeme mit mikroskopischen Methoden untersucht wurden, liegen detaillierte strukturelle Informationen vor. Es konnte gezeigt werden, dass die Adsorptionsenergie auf 3.4 nm großen Pd Nanopartikeln um 69 kJ/mol höher ist als auf Pd(111). Dieser Effekt resultiert aus der Änderung des Adsorptionsplatzes von Facettenplätzen auf Pd(111) zu Kantenplätzen auf Pd Nanopartikeln. Die Änderung der Partikelgröße im Bereich 3.4 nm - 1.9 nm führt zu einer Verringerung der Adsorptionsenergie um 70 kJ/mol. Eine Reduktion der Adsorptionsenergie auf kleineren Nanopartikeln wurde auch für CO gemessen. Die Differenz in der Pd-O Bindungsenergie zwischen den verschiedenen Systemen verringert sich bei erhöhter Adsorbatbedeckung. Die Anzahl adsorbierter Sauerstoffatome auf frisch präparierten Pd Nanopartikeln bei 300 K ist um drei bis vier mal höher als die Anzahl an Sauerstoffatomen welche Pd Oberflächenplätze sättigen können. Diese Beobachtung kann mit Sauerstoffdiffusion in die Nanopartikel oder in den Träger erklärt werden. Die Wechselwirkung zwischen Sauerstoff und CO auf Pd(111) und Pd Nanopartikeln verschiedener Größen wurde als Funktion der Bedeckung studiert. Aufgrund der CO-O Wechselwirkung verringert sich die CO Adsorptionsenergie um ~40 kJ/mol auf sauerstoffvorbedeckten Pd(111) und Pd Nanopartikeln der Größen 2.9 nm und 3.4 nm. / To determine the correlation between the particle size and the reactivity of Pd nanoparticles, which are supported on iron oxide, the experimental method single crystal adsorption calorimetry has been combined with the preparation of model systems. Detailed structural information on the supported systems is available from previous structural studies. It was found that the oxygen adsorption energy is 69 kJ/mol higher on 3.4 nm sized Pd nanoparticles compared to Pd(111) due to a change of the local adsorption site from threefold hollow to low coordinated sites. A reduction of the particle size in the range 3.4 nm - 1.9 nm was found to lead to a decrease of the adsorption energy by 70 kJ/mol. A reduction of the adsorbate binding energy has also been found for CO. The difference in the Pd-O binding energy between the different systems decreases with increasing coverage. It was demonstrated that the number of adsorbed oxygen atoms on freshly prepared Pd nanoparticles at 300 K is three to four times higher than the amount of oxygen atoms which saturate the Pd surface sites. This observation can be explained with oxygen diffusion either into the nanoparticles or into the support. The interaction between oxygen and CO has been studied on Pd(111) and Pd nanoparticles of different sizes as a function of the coverage. Due to CO-O interaction, the CO adsorption energy is reduced by ~40 kJ/mol on oxygen precovered Pd(111) and Pd nanoparticles of 2.9 nm and 3.4 nm.

The present work was initiated to investigate the surface- and interfacial phenomena for iron and slag/iron systems. The aim was to understand the mechanism of the effect of surface active elements on surface and interfacial properties. In the present work, the adsorption of oxygen and sulfur on iron surface as well as adatom surface movements were studied based on the ab initio method. BCC iron melting phenomena and sulfur diffusion in molten iron were investigated by Monte Carlo simulations. The impact of oxygen potential on interfacial mass transfer was carried out by X-ray sessile drop method. Firstly, the structural, electronic and magnetic properties as well as thermodynamic stability were studied by Density functional theory (DFT). The hollow site was found to be the most stable adsorption site both for oxygen and sulfur adsorbed on iron (100) surface, which is in agreement with the experiment. The relaxation geometries and difference charge density of the different adsorption systems were calculated to analyze the interaction and bonding properties between Fe and O/S. It can be found that the charge redistribution was related to the geometry relaxation. In addition, the sulfur coverage is considered from a quarter of one monolayer (1ML) to a full monolayer. It was found that the work function and its change Δφ increased with S coverage, in very good agreement with experiment. Due to a recent discussion regarding the influence of charge transfer on Δφ, it is shown in the present work that the increase in Δφ can be explained by the increasing surface dipole moment as a function of S coverage. S strongly interacts with the surface Fe layer and decreases the surface magnetic moment as the S coverage increases. Secondly, a two dimensional (2D) gas model based on density functional calculations combined with thermodynamics and statistical physics, was proposed to simulate the movement of the surface active elements, viz. oxygen and sulfur atoms on the Fe(100) surface. The average velocity of oxygen and sulfur atoms was found to be related to the vibration frequencies and energy barrier in the final expression developed. The calculated results were based on the density function and thermodynamics & statistical physics theories. In addition, this 2D gas model can be used to simulate and give an atomic view of the complex interfacial phenomena in the steelmaking refining process. A distance dependent atomistic Monte Carlo model was developed for studying the iron melting phenomenon as well as effect of sulfur on molten iron surface. The effect of boundary conditions on the melting process of an ensemble of bcc iron atoms has been investigated using a Lennard-Jones distance dependent pair potential. The stability of melting process was energetically and spatially analyzed under fixed wall and free surface conditions and the effects of short and long-range interactions were discussed. The role of boundary conditions was significantly reduced when long-range interactions were used in the simulation. This model was further developed for investigating the effect of sulfur on molten iron surface. A combination of fixed wall and free surface boundary condition was found to well-represent the molten bath configuration while considering the second nearest neighbor interactions. Calculations concerning the diffusion of sulfur on molten surface were carried out as a function of temperature and sulfur concentration. Our results show that sulfur atoms tended to diffuse away from the surface into the liquid bulk and the diffusion rate increased by increasing temperature. Finally, impact of oxygen potential on sulfur mass transfer at slag/metal interface, was carried out by X-ray sessile drop method. The movement of sulfur at the slag/metal interface was monitored in dynamic mode at temperature 1873 K under non-equilibrium conditions. The experiments were carried out with pure iron and CaO-SiO2-Al2O3-FeO slag (alumina saturated at the experimental temperature) contained in alumina crucibles with well-controlled partial pressures of oxygen and sulfur. As the partial pressure of oxygen increased, it was found that interfacial velocity as well as the oscillation amplitude increased. The thermo-physical and thermo-chemical properties of slag were also found to influence interfacial velocity. / QC 20101123

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High Performance Liquid Chromatography (HPLC) is a widely used tech-nique both for detecting and purifying substances in academy and in the industry. In order to facilitate the use of, and knowledge in HPLC, character-ization of stationary phases is of utmost importance. Tailor made characteri-zation methods and workflows are steadily increasing the speed and accura-cy in which new separation systems and methods are developed. In the field fundamental separation science and of preparative chromatography there is always the need for faster and more accurate methods of adsorption isotherm determination. Some of that demand are met with the steadily increase of computational power, but the practical aspects on models and methods must also be further developed. These nonlinear characterization methods will not only give models capable of describing the adsorption isotherm but also actual values of local adsorption energies and monolayer saturation capacity of an individual interaction sites etc.The studies presented in this thesis use modern alkali stable stationary phas-es as a model phase, which will give an insight in hybrid materials and their separation mechanism. This thesis will include an update and expansion in using the Elution by Characteristic Points (ECP) method for determination of adsorption isotherms. The precision is even further increased due to the ability to use slope data as well as an increase in usability by assigning a set of guidance rules to be applied when determine adsorption isotherms having inflection points. This thesis will further provide the reader with information about stationary phase characterization and the power of using existing tech-niques; combine them with each other, and also what the expansion of meth-ods can revile in terms of precision and increased usability. A more holistic view of what benefits that comes with combining a non-linear characteriza-tion of a stationary phase with more common linear characterization meth-ods are presented.