Sintesi e caratterizzazione di nanocompositi aerogel altamente porosi per applicazioni catalitiche

摘要

This thesis has focused on the synthesis, characterization and catalytic applications of nanocomposite aerogels, made out of an active nanophase dispersed in a highly porousudamorphous silica matrix. These nanocomposites have unique properties which mainly depend on the composition, size and distribution of the nanoparticles and on the morphology and porosity of the matrix. Highly porous MFe2O4-SiO2 (M = Co, Ni, Mn, Zn), NiCo2O4-SiO2, Fe/Mo-SiO2, CuO-SiO2, Cu2O-SiO2 eudCu-SiO2 nanocomposite aerogels, with variable amounts of dispersed phase, were prepared by a sol-gel procedure followed by supercritical drying and thermal treatments. This method is based on the co-hydrolysis and co-gelation of the precursors of the matrix and the dispersed phaseudthrough the pre-hydrolysis of the TEOS (tetraethoxysilane) under acid conditions followed by gelation under basic conditions, using urea as gelling agent. The detailed characterization of nanocomposite aerogels was carried out using a multitechnique approach involving conventional techniques, such as X-ray diffraction (XRD), nitrogenudphysisorption at 77 K and transmission electron microscopy (TEM), associated with more advanced techniques such as X-ray absorption spectroscopy (XAS), Mössbauer spectroscopy and SQUID magnetometry. These nanocomposites, thanks to their high porosity, low density and high area surface, wereudtested as catalysts in important industrial processes such as the synthesis of Carbon Nanotubes via Catalytic Chemical Vapour Deposition (CCVD) and the Water Gas Shift Reaction (WGSR), which plays an important role in the technology of fuel cells (FC), showing interesting catalytic activities.udThe tests for multiwall carbon nanotubes (MWCNT) production and for WGSR were performed in collaboration with the Applied and Environmental Chemistry Department of Szeged University (Hungary), the Chemistry Department of Rome University “La Sapienza” and the Chemical and Earth Science Department of Cagliari University.