Summary
A sequential analysis using Ultra-violet Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS) on ceria nanopowders has been implemented to identify the influence of the X-ray beam on the surface of this oxide. For the first time, UPS analysis evidenced the photoreductive effect of XPS analysis on ceria after an oxidative <i>in situ</i> pretreatment, leading to an overestimation of the Ce<sup>3+</sup>/Ce<sup>4+</sup> ratio obtained by XPS. Based on this spectroscopy methodology, UPS imposes itself as a leading technique for analyzing powders with minimal impact on the authentic chemical state, thus paving the way for identifying the real ratio of Ce<sup>4+</sup> and Ce<sup>3+</sup> of ceria after oxidative and reductive <i>in situ</i> treatments.
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