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The interaction between metal particles and the oxide support, the so-called metal-support interaction, plays a critical role in the performance of heterogenous catalysts. Probing the dynamic evolution of these interactions under reactive gas atmospheres is crucial to comprehending the structure-performance relationship and eventually designing new catalysts with enhanced properties. Cobalt supported on TiO 2 (Co/TiO 2 ) is an industrially relevant catalyst applied in Fischer-Tropsch synthesis. Although it is widely acknowledged that Co/TiO 2 is restructured during the reaction process, little is known about the impact of the specific gas phase environment at the material's surface. The combination of soft and hard X-ray photoemission spectroscopies are used to investigate in situ Co particles supported on pure and NaBH 4 -modified TiO 2 under H 2 , O 2 , and CO 2 :H 2 gas atmospheres. The combination of soft and hard X-ray photoemission methods, which allows for simultaneous probing of the chemical composition of surface and subsurface layers, is one of the study's unique features. It is shown that under H 2 , cobalt particles are encapsulated below a stoichiometric TiO 2 layer. This arrangement is preserved under CO 2 hydrogenation conditions (i.e., CO 2 :H 2 ), but changes rapidly upon exposure to O 2 . The pretreatment of the TiO 2 support with NaBH 4 affects the surface mobility and prevents TiO 2 spillover onto Co particles.

The development of Ce-based materials is directly dependent on the catalyst surface defects, which is caused by the calcination steps required to increase structural stability. At the same time, the evaluation of cerium's redox properties under reaction conditions is of increasing relevant importance. The synthesis of Ce-UiO-66 and CeZr-UiO-66 and their subsequent calcination are presented here as a simple and inexpensive approach for achieving homogeneous and stable CeO 2 and CeZrO x nanocrystals. The resulting materials constitute an ideal case study to thoroughly understand cerium redox properties. The Ce 3+ /Ce 4+ redox properties are investigated by H 2 -TPR experiments exploited by in situ FT-IR and Ce M 5 -edge AP-NEXAFS spectroscopy. In the latter case, Ce 3+ formation is quantified using the MCR-ALS protocol. FT-IR is then presented as a high potential/easily accessible technique for extracting valuable information about the cerium oxidation state under operating conditions. The dependence of the OH stretching vibration frequency on temperature and Ce reduction is described, providing a novel tool for qualitative monitoring of surface oxygen vacancy formation. Based on the reported results, the molecular absorption coefficient of the Ce 3+ characteristic IR transition is tentatively evaluated, thus providing a basis for future Ce 3+ quantification through FT-IR spectroscopy. Finally, the FT-IR limitations for Ce 3+ quantification are discussed.