Master degree in Materials Science

In heterogeneous catalysis, inorganic oxides are often used as inert media to disperse active species such as metallic nanoparticles, clusters or even single ions. How these active species are organised on the oxide surface and their spatial distribution is a central topic in the characterisation of catalytic systems, with implications on their performances. There exist a number of spectroscopic techniques that have been used to inform on the geometric distribution of active sites, but either they yield just local information or need highly ordered samples. This experimental thesis will explore the use of pulsed dipolar Electron Paramagnetic Resonance (EPR) spectroscopy to determine the distribution of active sites in the nanometer range. The method exploits the dipolar coupling between pairs of dipole moments associated to open-shell ions to return accurate distance determinations. The great advantage of this novel approach is that it reports on the long-range order of active sites in the nanometer range (up to 5 nm) and in disordered samples such as nanopowders.