| Autor: |
Salusso D; Department of Chemistry, NIS Center and INSTM Reference Center, University of Turin, 10125 Turin, Italy.; European Synchrotron Radiation Facility, CS 40220, CEDEX 9, 38043 Grenoble, France., Mauri S; IOM CNR Laboratorio TASC, AREA Science Park, Basovizza, 34149 Trieste, Italy.; Department of Physics, University of Trieste, Via Valerio 2, 34127 Trieste, Italy., Deplano G; Department of Chemistry, NIS Center and INSTM Reference Center, University of Turin, 10125 Turin, Italy., Torelli P; IOM CNR Laboratorio TASC, AREA Science Park, Basovizza, 34149 Trieste, Italy., Bordiga S; Department of Chemistry, NIS Center and INSTM Reference Center, University of Turin, 10125 Turin, Italy., Rojas-Buzo S; Department of Chemistry, NIS Center and INSTM Reference Center, University of Turin, 10125 Turin, Italy. |
| Abstrakt: |
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. |
