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Cerium-based Metal Organic Frameworks with UiO-66 Architecture
Summary:
The authors from Christian-Albrechts-Universität zu Kiel, KU Leuven, and other institutions developed a series of Ce(IV)-based metal–organic frameworks (MOFs) with UiO-66 architecture, exhibiting redox activity and porosity, achieving high catalytic performance in aerobic alcohol oxidation.
Background:
1. To address the limited availability of redox-active MOFs based on Ce(IV), previous researchers explored Zr- and other metal-based UiO-66 analogs, achieving structural stability and catalytic versatility, yet Ce(IV) analogs remained underdeveloped due to cluster stability issues.
2. The authors proposed a mild and rapid synthesis method to stabilize the [Ce₆O₄(OH)₄]¹²⁺ cluster and successfully obtained isoreticular Ce-UiO-66 MOFs with various linkers and functional groups.
Research Content:
1. Synthesis:
The authors synthesized Ce-UiO-66 MOFs using cerium(IV) ammonium nitrate and dicarboxylic acid linkers (e.g., BDC, Fum, NDC, BPDC) via a short (15 min), low-temperature (100 °C) solvothermal method.
2. Characterizations:
1) BET analysis revealed specific surface areas up to 1282 m²/g and micropore volumes around 0.50 cm³/g.
2) SEM showed spherical particle agglomerates with sizes of 100–500 nm.
3) XANES confirmed the exclusive presence of Ce(IV); PXRD and TGA indicated structural stability up to ~300 °C and defect-rich frameworks.
3. Application:
The Ce-UiO-66-BDC/TEMPO system was applied in the aerobic oxidation of benzyl alcohol, achieving 88% conversion and 100% selectivity to benzaldehyde under optimized conditions.
4. Mechanism:
A redox mechanism was proposed where Ce(IV) centers on the MOF surface oxidize TEMPO to its oxoammonium form, which then oxidizes benzyl alcohol to benzaldehyde, with Ce(III) being reoxidized by O₂. The synergy between Ce-MOF and TEMPO is essential for high activity.
Outlook:
This work demonstrates the successful integration of Ce(IV) into UiO-66 frameworks, expanding the library of redox-active MOFs. The materials show promise in oxidative catalysis and potentially other redox-based applications, with tunability via linker functionalization and pore size control.
Cerium-based Metal Organic Frameworks with UiO-66 Architecture: Synthesis, Properties and Redox Catalytic Activity
Authors: Martin Lammert, Michael T. Wharmby, Simon Smolders, Bart Bueken, Alexandra Lieb, Kirill A. Lomachenko, Dirk De Vos, Norbert Stock
DOI: 10.1039/c5cc02606g
Link: https://pubs.rsc.org/en/content/articlelanding/2015/cc/c5cc02606g
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