Hierarchical materials for energy and environmental applications

The research activity of the present thesis has focused on the development of carbon/inorganic hierarchical nanostructured hybrids to be employed as catalysts for two important energy processes: the water-gas shift reaction (WGSR) and the photocatalytic hydrogen production from renewable sources, such as biomass-derived oxygenated compounds (i.e. ethanol and glycerol). The design of the nanohybrids follows a specific hierarchy where a carbon component, consisting of properly functionalized multiwalled carbon nanotubes (MWCNTs) or carbon nanocones (CNCs), is used as scaffold for an inorganic phase that acts as the catalyst/cocatalyst. The inorganic phase in turns consist of noble metal nanoparticles (i.e. palladium) enclosed into a mesoporous metal oxide. The functionalization of the carbon components serves to equip the nanocarbon with anchor points for the metal phase and to enhance dispersion in liquid media. The as-prepared ternary hybrid is then subjected to specific thermal treatments, with the temperature chosen on the basis of thermogravimetric analysis, in order to crystallize the metal oxide phase and remove the organic ligands. The final catalyst package has shown remarkable catalytic features in both the investigated processes, confirming that the presence of the nanocarbon scaffold and the specific hierarchy result in a large improvement of the performance as compared to state-of-the art catalysts. Such improvement is related to the excellent electronic properties of the carbon nanostructures as well as to their ability to enhance robustness and stability of the inorganic phase. More specifically, CeO2-based catalysts display an increased activity and stability in the WGSR, while the TiO2-based photocatalysts were successfully used in the photocatalytic production of H2 with very high productivity. Characterization of the materials has been carried out through several techniques including HR-TEM, EDX mapping, XRD, microRaman, physi- and chemi-sorption analysis and TGA, which confirmed the obtainment of the desired assembly.