Hydrodesulfurization (HDS) is an ubiquitous part of oil refining that ensures that fuels are cleaned of impurities and environment release of pollutants such as SOx and NOx gasses are minimized. In... Show moreHydrodesulfurization (HDS) is an ubiquitous part of oil refining that ensures that fuels are cleaned of impurities and environment release of pollutants such as SOx and NOx gasses are minimized. In this thesis, atomic level insights into the process of HDS are gained by exploring various methods of generating the catalytically active CoMoS phase as well as the effect of the reaction gasses like hydrogen and methylthiol on the atomic structure of the catalyst at industrially relevant conditions. For this purpose, a variety of techniques such as high-pressure scanning tunneling microscopy, X-ray photoelectron spectroscopy and electron diffraction are used. Furthermore, the studies presented in this thesis make several steps towards bridging the pressure and materials gap between the fundamental catalysis studies and industrial catalytic conditions. The results of this work pave way for more fundamental research with the help of theoretical methods such as DFT calculations which can help with designing more efficient catalysts to meet the future demands of clean fuels. Show less
Here we present the results of a study carried out to investigate the simultaneous sulfidation of Co and Mo oxide nanoparticles on Au(111) as a synthesis strategy to prepare a model catalyst for... Show moreHere we present the results of a study carried out to investigate the simultaneous sulfidation of Co and Mo oxide nanoparticles on Au(111) as a synthesis strategy to prepare a model catalyst for hydrodesulfurization (HDS). We make use of scanning tunneling microscopy and X-ray photoelectron spectroscopy to track the changes in morphology and chemistry during the synthesis of a mixed Mo and Co oxide precursor and the sulfidation thereafter, to the respective sulfides. We investigated the effects of temperature and the duration of sulfidation on the completeness of the sulfidation process. Our study shows that the formation of MoS2 with the CoMoS edge (the desired model catalyst) is not affected by the time or the temperature of sulfidation. However, the yield of the Co-promoted MoS2 slabs is limited by the formation of large clusters due to the spreading of Mo and Co oxide phases upon sulfidation. Complete sulfidation of the mixed oxide precursor to Co-promoted MoS2 can be accelerated by increasing the sulfidation temperature to 730 K due to the thermally activated nature of Mo oxide sulfidation. Thus, we demonstrate that using a mixed Mo and Co oxide precursor as a starting point for the Co-promoted MoS2 phase for fundamental catalytic studies is a viable strategy. Show less
Stability of quantum dot (QD) films is an issue of concern for applications in devices such as solar cells, LEDs, and transistors. This paper analyzes and optimizes the passivation of such QD films... Show moreStability of quantum dot (QD) films is an issue of concern for applications in devices such as solar cells, LEDs, and transistors. This paper analyzes and optimizes the passivation of such QD films using gas-phase deposition, resulting in enhanced stability. Crucially, we deposited alumina at economically attractive conditions, room temperature and atmospheric pressure, on (1,2-ethanediamine) capped PbSe QD films using an approach based on atomic layer deposition (ALD), with trimethylaluminum (TMA) and water as precursors. We performed coating experiments from 1 to 25 cycles on the QD films, finding that alumina formed from the first exposure of TMA. X-ray photoelectron spectroscopy points to the presence of oxygen-rich compounds on the bare QD films, most likely from entrapped solvent molecules during the assembly of the QD films. These oxygenated compounds and the amine groups of the organic ligands react with TMA in the first cycle, resulting in a fast growth of alumina. Using 10 cycles resulted in a QD film that was optically stable for at least 27 days. Depositing alumina at ambient conditions is preferred, since the production of the QD films is also carried out at room temperature and atmospheric pressure, allowing combination of both processes in a single go. Show less
