New insights on the defect sites evolution during CO oxidation over doped ceria nanocatalysts probed by in situ Raman spectroscopy

Among the factors affecting ceria activity, the defectiveness plays a key role in the case of CO oxidation. In this study, its connection with the catalytic performance was investigated via in-situ Raman spectroscopy on nanostructured pure and Cu/Mn-doped ceria, monitoring the defect sites and surface species evolution during the reaction. The accumulation of polyene-like chains, formed through CO dissociative adsorption at the catalyst surface, was observed and their disappearance was related to the catalyst light-off temperature. Moreover, the doped samples exhibited a rise of the Raman bands associated to defects after the tests, consequence of the structural rearrangements occurring during CO oxidation. Indeed, in-situ Raman measurements during reduction (CO/N2) and oxidation cycles at 400 °C evidenced the formation of oxygen vacancy clusters in reducing atmosphere, which could reorganize not only in O2 but also upon a temperature decrease, forming isolated vacancies and then evolving in Frenkel and extrinsic oxidized dopant-containing sites when exposed to oxygen.