Unraveling the reversible formation of defective Ce3+ sites in the UiO-66(Ce) material: a multi-technique study. (January 2023)

• Record Type: Journal Article
• Authors: Rojas-Buzo, S.; Salusso, D.; Bonino, F.; Paganini, M.C.; Bordiga, S.
• Is Part Of: Materials today chemistry. Volume 27(2023)
• Publication Date: 2023-01
• Subjects: Metal-organic framework -- Ce-MOF -- Ce reduction -- Laboratory techniques -- NEXAFS; Chemistry -- Periodicals; Materials -- Research -- Periodicals; Materials science -- Periodicals; Chemistry; Materials -- Research; Electronic journals; Periodicals; 660.282
• DOI: 10.1016/j.mtchem.2022.101337
• Languages: English
• ISSNs: 2468-5194

Abstract

Abstract: Ce 3+ presence and formation in Ce-based UiO-66 Metal-Organic Framework (MOF) still presents a debated evaluation between the employed characterization techniques. In this work, we have prepared a defective UiO-66(Ce) and investigated the nature of Ce 3+ sites on the CeOx clusters. Laboratory techniques (EPR, XPS, UV–Vis and FTIR spectroscopy) were compared with operando Ce M5 -edge NEXAFS to study Ce 3+ accessibility. All the employed techniques presented different degrees of accessibility or reliability (e.g., sample damage or not sufficient sensitivity). Among the obtained results, EPR, UV–Vis and NEXAFS spectroscopies unraveled Ce 4+ →Ce 3+ conversion during the sample dehydration. The MOF structure was not damaged by neither water loss nor the beam, directly relating Ce oxidation state to the water content, opening a new route to both synthesis of stable and active MOFs and non-invasive characterization strategies. Finally, laboratory measurements considerations were exploited for studying Ce 3+ formation in Zr-doped UiO-66(Ce) samples. Graphical abstract: Image 1 Highlights: The redox nature of the UiO-66(Ce) material was deeply studied by using multiple laboratory techniques. The Ce 4+ to Ce 3+ conversion occurs on the cluster during the thermal activation of the MOF. Handy techniques, including UV–Vis and FTIR spectroscopy, can qualitative verify the Ce 3+ formation. Ce M5 -edge NEXAFS with MCR-ALS analysis can provide the concentration profile of the redox species during the activation. The presence of Ce 3+ is also detected in UiO-66(Ce/Zr) materials where the Ce is very diluted with Zr.