The Remarkable Amphoteric Nature of Defective UiO‐66 in Catalytic Reactions

• Published in: ChemCatChem Vol. 9; no. 12; pp. 2203 - 2210
• Main Authors: Hajek, Julianna, Bueken, Bart, Waroquier, Michel, De Vos, Dirk, Van Speybroeck, Veronique
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 22.06.2017; John Wiley and Sons Inc
• Subjects: Alcohols; Amphoterics; Basicity; Bricks; brønsted base site; Catalysis; Catalysts; Catalytic activity; Chemical reactions; Dehydration; Density functional theory; DFT; kinetics; lewis acid site; Oxidation; Zirconium; catalysis; DFT; kinetics; lewis acid site; brønsted base site
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201601689

One of the major requirements in solid acid and base catalyzed reactions is that the reactants, intermediates or activated complexes cooperate with several functions of catalyst support. In this work the remarkable bifunctional behavior of the defective UiO‐66(Zr) metal organic framework is shown for acid‐base pair catalysis. The active site relies on the presence of coordinatively unsaturated zirconium sites, which may be tuned by removing framework linkers and by removal of water from the inorganic bricks using a dehydration treatment. To elucidate the amphoteric nature of defective UiO‐66, the Oppenauer oxidation of primary alcohols has been theoretically investigated using density functional theory (DFT) and the periodic approach. The presence of acid and basic centers within molecular distances is shown to be crucial for determining the catalytic activity of the material. Hydrated and dehydrated bricks have a distinct influence on the acidity and basicity of the active sites. In any case both functions need to cooperate in a concerted way to enable the chemical transformation. Experimental results on UiO‐66 materials of different defectivity support the theoretical observations made in this work. Working together: The bifunctional behavior of the defective UiO‐66(Zr) metal organic framework was theoretically studied through the Oppenaur oxidation of primary alcohols. The presence of acid and base centers within molecular distances is shown to be essential in the performance of the catalytic reaction as they cooperate in a concerted way during the chemical transformation.