Immagazzinamento di ossigeno in CeO2/Pt: Spettroscopia ad assorbimento a raggi X e studi di Density functional theory

In the last decades, there is an ongoing discussion about environmental and energy safety problem. This thesis is going to show the study on CeO2 as one of the possible candidate for both cases. The importance of ceria is given by its ability to store and release oxygen reversible. Main purpose of this work is to understand low temperature oxygen storage capacity (LT OSC) mechanism and the related structure of the reduced ceria surface on the atomic scale. The sample used is CeO2 nanorods promoted with Pt nanoparticles at different chemical environments and temperatures and, as references, CeO2 from NIST (National Institute of Standards and Technology), CeO2 rods, CeAlO3, Ce2Zr2O7. The CeO2 is considered for Ce4+, CeAlO3 for Ce3+, and instead in Ce2Zr2O7 both Ce3+ and Ce4+ are present. High energy resolution fluorescence detector (HERFD) XANES spectra at the Ce L1 and L3 edges were measured at the SuperXAS beamline at SLS (PSI, Villigen, Switzerland) and soft X-ray absorption Max Lab II (Lund, Sweden) at I1011 beamline at Ce M4 and M5 edges and at O K edge. We have observed the Ce3+ defect formation in situ and estimated the concentration of oxygen vacancy as a function of applied temperature and elapsed time. In order to study the LT OSC process theoretically the DFT simulations were carried out using pseudopotential plane wave approximation. Following structures were considered used in simulations: pure CeO2 bulk, CeO2 (111) surface, Ce2O3 hexagonal and cubic, Ce11O20, and 2x2x2 supercell of CeO2 with O vacancy. Atomic structure, DOS and bandstructure has been derived and then compared with experimental data.