| Vanadium oxide (VOx) catalysts are of great importance as catalysts in the manufacture of important chemicals (e.g. sulfuric acid, phtalic anhydride) and the reduction of environmental pollution (e.g. removal of NO x from flue gas of power plants). A supported VOx catalyst consists of a two-dimensional surface overlayer of active species, deposited on a high surface area support. This way, the catalytic activity, mechanical strength and thermal stability of the active phase is improved. The catalytic performance of a heterogeneous catalyst system is mainly determined by its surface structure and morphology. Only a uniform and disperse catalyst surface layer ensures a good accessibility of the active sites and an optimal interaction with the support. Therefore, there is a continuing need to develop new synthesis methods that allow precise control of structure and morphology. In this Ph.D. work, a new preparation method is introduced: the Molecular Designed Dispersion (MDD), based on the adsorption and subsequent thermal conversion of a neutral vanadyl acetylacetonate complex (VO(acac)2). This method gives a higher degree of control of the anchorage and the surface dispersion of the supported transition metal oxide phase. The presented work describes the fundamental study of the modification process and the investigation of its potentials and possible applications. This novel MDD method was also employed in the synthesis of supported mixed oxide systems. A mixture of several metal oxides at synergetic ratios can result in catalysts with exceptionally good catalytic performance. For the first time supported vanadia-tantala (VO x-TaOx) catalysts have been studied. In various catalytic processes, not only the surface structure of the catalyst is of importance, but also the nature of the bulk phase. In the chemical and pharmaceutical industry there is a growing need for materials with large pore diameter and well-ordered pore channels, in order to process efficiently large sized molecules. In the early 90's, a new family of mesoporous crystalline silicates has been discovered. These socalled M41S materials, like MCM-41 and MCM-48, show unique structural properties, making them potentially useful for catalytic applications. Based on the knowledge of the molecular designed dispersion of VO(acac) 2 on common oxide supports, new insights are obtained on the nature of the highly reactive MCM-48 surface and the structure and activity of MCM-48 supported VOx. In addition, a process is presented for the simultaneous stabilization and activation of these materials, involving multifunctional coupling reagents. |
