In this research project, silica-supported Ziegler-Natta and metallocene-based polymerization catalysts are studied in the early stages of active sites genesis and polymer formation. In order to do so, a multi-scale characterization approach under reaction conditions is adopted, featuring various spectroscopy and microscopy techniques. The ultimate aim is to establish correlation between the macroscopic physical (e.g. support fragmentation, temperature gradients), macroscopic chemical (e.g. polymer composition, type, density) and nanoscopic chemical properties (e.g. oxidation state, coordination environment, ligand interaction) of the catalyst systems of interest. Within this research project, we work closely together with the group of Professor Elena Groppo at the University of Torino (Italy).