Journal
CHEMICAL SCIENCE
Volume 5, Issue 11, Pages 4517-4524Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4sc01731e
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Funding
- Belgian Federal Government [07/05]
- KU Leuven
- FWO Vlaanderen [G.0453.09, G.0486.12]
- FWO Vlaanderen
- Research Board of Ghent University (BOF)
- European Research Council under the European Community [240483]
- European Research Council [307523]
- Fonds voor Wetenschappelijk Onderzoek [G0197.11, G.0962.13]
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A new method has been developed for generating highly dispersed base sites on metal-organic framework (MOF) lattices. The base catalytic activity of two alkaline earth MOFs, M-2(BTC)(NO3)(DMF) (M = Ba or Sr, H3BTC = 1,3,5-benzenetricarboxylic acid, DMF = N,N-dimethylformamide) was studied as a function of their activation procedures. The catalytic activity in Knoevenagel condensation and Michael addition reactions was found to increase strongly with activation temperature. Physicochemical characterization using FTIR, C-13 CP MAS NMR, PXRD, XPS, TGA-MS, SEM, EPR, N-2 physisorption and nitrate content analysis shows that during activation, up to 85% of the nitrate anions are selectively removed from the structure and replaced with other charge compensating anions such as O-2(-). The defect sites generated via this activation act as new strong basic sites within the catalyst structure. A fluorescence microscopic visualization of the activity convincingly proves that it is exclusively associated with the hexagonal crystals, and that reaction proceeds inside the crystal's interior. Theoretical analysis of the Ba-material shows that the basicity of the proposed Ba2+-O2--Ba2+ motifs is close to that of the edge sites in BaO.
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