期刊
CHEMPHYSCHEM
卷 19, 期 4, 页码 373-378出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201700967
关键词
catalysis; cerium; metal-organic frameworks; redox chemistry; X-ray spectroscopy
资金
- FWO Flanders
- Russian Federation Government [14.Y26.31.0001]
The introduction of Ce4+ as a structural cation has been shown to be a promising route to redox active metal-organic frameworks (MOFs). However, the mechanism by which these MOFs act as redox catalysts remains unclear. Herein, we present a detailed study of the active site in [Ce6O4(OH)(4)]-based MOFs such as Ce-UiO-66, involved in the aerobic oxidation of benzyl alcohol, chosen as a model redox reaction. X-ray absorption spectroscopy (XAS) data confirm the reduction of up to one Ce4+ ion per Ce-6 cluster with a corresponding outwards radial shift due to the larger radius of the Ce3+ cation, while not compromising the structural integrity of the framework, as evidenced by powder X-ray diffraction. This unambiguously demonstrates the involvement of the metal node in the catalytic cycle and explains the need for 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a redox mediator to bridge the gap between the one-electron oxidation of the Ce4+/Ce3+ couple and the two-electron alcohol oxidation. Finally, an improved catalytic system with Ce-MOF-808 and TEMPO was developed which outperformed all other tested Ce4+-MOFs.
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