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ABSTRACT: The effect of a post-synthetic acid treatment on the catalytic performance of MOFs is evaluated for MIL-100(Fe), an iron-benzenetricarboxylate. The acid-treated frameworks are structurally robust as no differences have been found in XRD patterns after treatment. Porosity of the acid-treated MOFs gradually decreases, most probably as a consequence of anions remaining in the charged frameworks. Monitoring the modification of the MOFs by reactions of which the outcome depends on the acid properties of the catalyst suggests the presence of two types of active sites, with weak Bronsted acid sites in close vicinity to the Lewis acid open metal sites. This is supported by CO-chemisorption experiments which indicate a large increase of both Lewis and Bronsted acidity. In Diels-Alder reactions of oxygenated dienophiles with 1,3-cyclohexadiene, a strong increase of the activity is found for the acid-treated MOFs. This is explained by the enhanced activation of the dienophiles on the modified active sites.
J. Mater. Chem. 01/2012; 22(20):10313-10321.
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07/2011: pages 191 - 212; , ISBN: 9783527635856
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Michael Maes,
Maarten Trekels,
Mohammed Boulhout,
Stijn Schouteden,
Frederik Vermoortele, Luc Alaerts,
Daniela Heurtaux,
You-Kyong Seo,
Young Kyu Hwang,
Jong-San Chang,
Isabelle Beurroies,
Renaud Denoyel,
Kristiaan Temst,
Andre Vantomme,
Patricia Horcajada,
Christian Serre,
Dirk E De Vos
Angewandte Chemie International Edition 04/2011; 50(18):4210-4. · 13.45 Impact Factor
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ABSTRACT: The water-stable metal-organic framework MIL-53(Cr) is able to adsorb phenol and p-cresol from contaminated water as well as the monomeric sugar D-(-)-fructose. Based on the isotherm for phenol uptake from the liquid phase, it is proposed that the framework breathes to maximize the uptake.
Physical Chemistry Chemical Physics 02/2011; 13(13):5587-9. · 3.57 Impact Factor
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ABSTRACT: The metal-organic frameworks MIL-47 (V(IV)O{O(2)C-C(6)H(4)-CO(2)}) and MIL-53(Al) (Al(III)(OH)·{O(2)C-C(6)H(4)-CO(2)}) are capable of separating ethylbenzene and styrene. Both materials adsorb up to 20-24 wt % of both compounds. Despite the fact that they have identical building schemes, the reason for preferential adsorption of styrene compared to ethylbenzene is very different for the two frameworks. For MIL-47, diffraction experiments reveal that styrene is packed inside the pores in a unique, pairwise fashion, resulting in separation factors as high as 4 in favor of styrene. These separation factors are independent of the total amount of adsorbate offered. This is due to co-adsorption of ethylbenzene in the space left available between the packed styrene pairs. The separation is of a non-enthalpic nature. On MIL-53, the origin of the preferential adsorption of styrene is related to differences in enthalpy of adsorption, which are based on different degrees of framework relaxation. The proposed adsorption mechanisms are in line with the influence of temperature on the separation factors derived from pulse chromatography: separation factors are independent of temperature for MIL-47 but vary with temperature for MIL-53. Finally, MIL-53 is also capable of removing typical impurities like o-xylene or toluene from styrene-ethylbenzene mixtures.
Journal of the American Chemical Society 10/2010; 132(43):15277-85. · 9.91 Impact Factor
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ABSTRACT: This work studies the liquid phase separation of styrene and ethylbenzene on the metal−organic framework [Cu3(BTC)2] (BTC = 1,3,5-benzenetricarboxylate) as well as the analogous separation of vinyltoluenes from ethyltoluenes. Batch and column experiments have been performed to demonstrate the capacity of the material to separate styrene and ethylbenzene. Adsorption capacities of around 20 wt % are measured, while separation factors reach values as high as 5.5. As is demonstrated by UV−vis absorption measurements, the adsorption mechanism is based on specific interactions between the free Cu2+ ligation sites of the framework and the π-electrons of the aromatic compounds. For the separation of the vinyltoluenes and ethyltoluenes, similar capacities and separation factors have been obtained as for the separation of styrene and ethylbenzene, which suggests an analogous adsorption mechanism.
08/2010;
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07/2010: pages 73 - 94; , ISBN: 9783527630882
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Advanced Materials 06/2010; 22(24):2685-8. · 13.88 Impact Factor
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ABSTRACT: A new method based on patterned metallization and galvanic displacement is demonstrated to easily deposit patterned thin films of the metal-organic framework [Cu(3)(BTC)(2)].
Chemical Communications 06/2010; 46(21):3735-7. · 6.17 Impact Factor
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ABSTRACT: This work studies the liquid-phase separation of the aliphatic C(5)-diolefins, mono-olefins, and paraffins, a typical feed produced by a steam cracker, with a focus on the seldomly studied separation of the C(5)-diolefin isomers isoprene, trans-piperylene, and cis-piperylene. Three adsorbents are compared: the metal-organic framework MIL-96, which is an aluminum 1,3,5-benzenetricarboxylate, and two zeolites with CHA and LTA topology. All three materials have spacious cages that are accessible via narrow cage windows with a diameter of less than 0.5 nm. The mechanisms determining adsorption selectivities on the various materials are investigated. Within the diolefin fraction, MIL-96 and chabazite preferentially adsorb trans-piperylene from a mixture containing all three C(5)-diolefin isomers with high separation factors and a higher capacity compared to the reference zeolite 5A due to a more efficient packing of the trans isomer in the pores. Additionally, chabazite is able to separate cis-piperylene and isoprene based on size exclusion of the branched isomer. This makes chabazite suitable for separating all three diolefin isomers. Its use in separating linear from branched mono-olefins and paraffins is addressed as well. Furthermore, MIL-96 is the only material capable of separating all three diolefin isomers from C(5)-mono-olefins and paraffins. Finally, the MOF [Cu(3)(BTC)(2)] (BTC = benzene-1,3,5-tricarboxylate) is shown to be able to separate C(5)-olefins from paraffins. On the basis of these observations, a flow scheme can be devised in which the C(5)-fraction can be completely separated using a combination of MOFs and zeolites.
Journal of the American Chemical Society 02/2010; 132(7):2284-92. · 9.91 Impact Factor
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ABSTRACT: This work studies the liquid-phase separation of the aliphatic C5-diolefins, mono-olefins, and paraffins, a typical feed produced by a steam cracker, with a focus on the seldomly studied separation of the C5-diolefin isomers isoprene, trans-piperylene, and cis-piperylene. Three adsorbents are compared: the metal−organic framework MIL-96, which is an aluminum 1,3,5-benzenetricarboxylate, and two zeolites with CHA and LTA topology. All three materials have spacious cages that are accessible via narrow cage windows with a diameter of less than 0.5 nm. The mechanisms determining adsorption selectivities on the various materials are investigated. Within the diolefin fraction, MIL-96 and chabazite preferentially adsorb trans-piperylene from a mixture containing all three C5-diolefin isomers with high separation factors and a higher capacity compared to the reference zeolite 5A due to a more efficient packing of the trans isomer in the pores. Additionally, chabazite is able to separate cis-piperylene and isoprene based on size exclusion of the branched isomer. This makes chabazite suitable for separating all three diolefin isomers. Its use in separating linear from branched mono-olefins and paraffins is addressed as well. Furthermore, MIL-96 is the only material capable of separating all three diolefin isomers from C5-mono-olefins and paraffins. Finally, the MOF [Cu3(BTC)2] (BTC = benzene-1,3,5-tricarboxylate) is shown to be able to separate C5-olefins from paraffins. On the basis of these observations, a flow scheme can be devised in which the C5-fraction can be completely separated using a combination of MOFs and zeolites.
01/2010;
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ABSTRACT: Vapour-phase adsorption and separation of the C8 alkyl aromatic compounds p-xylene, m-xylene, o-xylene, and ethylbenzene has been studied on the metal-organic framework MIL-53. Adsorption and desorption isotherms of the pure components at 110 degrees C were determined using the gravimetric technique. The adsorption isotherms show two well-defined steps and hysteresis, corresponding to the opening or breathing of the framework, as induced by the presence of the adsorbing molecules. In the first isotherm plateau, an adsorption capacity of about 18 wt % is observed. After the breathing phenomenon, the adsorption capacity increases to about 40 wt %. Breakthrough separation experiments with equimolar o-xylene/ethylbenzene mixtures were performed at 110 degrees C with varying hydrocarbon pressures. The separation mechanism is related to the state of the pore structure, as dictated by framework breathing. At low pressure, below the "pore-opening" pressure, MIL-53 shows no preference for any isomer. At pressures high enough to induce pore opening, separation of the C8 alkyl aromatic isomers becomes possible and separation factors as high as 6.5 are observed. The separation at a high degree of pore filling in the open form is a result of differences in the packing modes of the C8 alkyl aromatic components in the pores of MIL-53.
Chemistry 07/2009; 15(31):7724-31. · 5.93 Impact Factor
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ABSTRACT: Three metal-organic frameworks (MOFs) with similar pore window diameters, [Cu(3)(BTC)(2)], MIL-47 and MIL-53(Al), are tested for adsorption of olefins, alkylnaphthalenes and dichlorobenzenes in the liquid phase. Selective adsorption of olefins is possible only on [Cu(3)(BTC)(2)] viapi-complexation on its open metal sites. This material shows a remarkable preference for cis-olefins over trans-olefins. All three MOFs have high affinities for alkylnaphthalene and dichlorobenzene isomers. Separation of 1,4-dimethylnaphthalene from other alkylnaphthalene isomers and of p- and m-dichlorobenzene can be carried out on both MIL-47 and MIL-53(Al), as shown with breakthrough experiments. For the alkylnaphthalenes, column experiments at different concentrations point to enthalpic interactions as important factors determining selectivity, and the occurrence of steric effects during the adsorption of 1,4-dimethylnaphthalene shows that its kinetic diameter approaches the pore diameter of the adsorbents. For the dichlorobenzenes, packing effects dominate the adsorption selectivity.
Physical Chemistry Chemical Physics 05/2009; 11(16):2903-11. · 3.57 Impact Factor
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ABSTRACT: The metal-organic framework MIL-53(Al) was tested for selective adsorption and separation of xylenes and ethylbenzene, ethyltoluenes, and cymenes using batch, pulse chromatographic, and breakthrough experiments. In all conditions tested, MIL-53 has the largest affinity for the ortho-isomer among each group of alkylaromatic compounds. Separations of the ortho-compounds from the other isomers can be realized using a column packed with MIL-53 crystallites. As evidenced by Rietveld refinements, specific interactions of the xylenes with the pore walls of MIL-53 determine selectivity. In comparison with the structurally similar metal-organic framework MIL-47, the selectivities among alkylaromatics found for MIL-53 are different. Separation of ethyltoluene and cymene isomers is more effective on MIL-53 than on MIL-47; the pores of MIL-53 seem to be a more suitable environment for hosting the larger ethyltoluene and cymene isomers than those of MIL-47.
Journal of the American Chemical Society 11/2008; 130(43):14170-8. · 9.91 Impact Factor
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ABSTRACT: The metal−organic framework MIL-53(Al) was tested for selective adsorption and separation of xylenes and ethylbenzene, ethyltoluenes, and cymenes using batch, pulse chromatographic, and breakthrough experiments. In all conditions tested, MIL-53 has the largest affinity for the ortho-isomer among each group of alkylaromatic compounds. Separations of the ortho-compounds from the other isomers can be realized using a column packed with MIL-53 crystallites. As evidenced by Rietveld refinements, specific interactions of the xylenes with the pore walls of MIL-53 determine selectivity. In comparison with the structurally similar metal−organic framework MIL-47, the selectivities among alkylaromatics found for MIL-53 are different. Separation of ethyltoluene and cymene isomers is more effective on MIL-53 than on MIL-47; the pores of MIL-53 seem to be a more suitable environment for hosting the larger ethyltoluene and cymene isomers than those of MIL-47.
09/2008;
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ABSTRACT: Vapor-phase adsorption and separation of the C8 alkylaromatic components p-xylene, m-xylene, o-xylene, and ethylbenzene on the metal-organic framework MIL-47 have been studied. Low coverage Henry adsorption constants and adsorption enthalpies were determined using the pulse chromatographic technique at temperatures between 230 and 290 degrees C. The four C8 alkylaromatic components have comparable Henry constants and adsorption enthalpies. Adsorption isotherms of the pure components were determined using the gravimetric technique at 70, 110, and 150 degrees C. The adsorption capacity and steepness of the isotherms differs among the components and are strongly temperature dependent. Breakthrough experiments with several binary mixtures were performed at 70-150 degrees C and varying total hydrocarbon pressure from 0.0004 to 0.05 bar. Separation of the different isomers could be achieved. In general, it was found that the adsorption selectivity increases with increasing partial pressure or degree of pore filling. The separation at a high degree of pore filling in the vapor phase is a result of differences in packing modes of the C8 alkylaromatic components in the pores of MIL-47.
Journal of the American Chemical Society 07/2008; 130(22):7110-8. · 9.91 Impact Factor
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ABSTRACT: The capacity and selectivity of the metal-organic framework MIL-47 for liquid phase adsorption are shown to heavily depend on the pretreatment of the material, as illustrated in detail by the particular case of selective xylene adsorption. By totally removing the uncoordinated terephthalic acid from the pores and simultaneously avoiding oxidation to nonporous V(2)O(5), pore volume and uptake of xylenes can be maximized. The presence of uncoordinated terephthalic acid in the pores improves the selectivity between p- and m-xylene. Calcination bed thickness and oven geometry influence the optimal calcination procedure. The physicochemical modifications of MIL-47 during its activation are investigated in detail with XRD, SEM, nitrogen physisorption, TGA and diffuse reflectance UV-Vis spectroscopy. Using optimally pretreated MIL-47 as adsorbent for xylene, ethyltoluene, dichlorobenzene, toluidine or cresol isomers, the para-isomer is in each case preferred over the meta-isomer in pulse chromatographic and batch experiments. The role of stacking in the selective adsorption of these isomers is discussed. In the case of the dichlorobenzenes, the meta- and para-isomers can be separated in a breakthrough experiment with a selectivity of 5.0.
Physical Chemistry Chemical Physics 06/2008; 10(20):2979-85. · 3.57 Impact Factor
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ABSTRACT: Reliable strategies are presented for the immobilization of molecular catalysts for selective oxidation in the liquid phase. Besides classical strategies such as ion exchange or covalent anchoring, new approaches are emerging, e.g. based on supported ionic-liquid phases or on incorporation of the active centre in a coordination polymer or a metal-organic framework.
Chemical Communications 05/2008; · 6.17 Impact Factor
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Luc Alaerts,
Christine E A Kirschhock,
Michael Maes,
Monique A van der Veen,
Vincent Finsy,
Anouschka Depla,
Johan A Martens,
Gino V Baron,
Pierre A Jacobs,
Joeri F M Denayer,
Dirk E De Vos
Angewandte Chemie International Edition 02/2007; 46(23):4293-7. · 13.45 Impact Factor
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ABSTRACT: An optimized procedure was designed for the preparation of the microporous metal-organic framework (MOF) [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number of Cu2O impurities, and particularly on the free CuII coordination sites in the framework. [Cu3(btc)2] is a highly selective Lewis acid catalyst for the isomerization of terpene derivatives, such as the rearrangement of alpha-pinene oxide to campholenic aldehyde and the cyclization of citronellal to isopulegol. By using the ethylene ketal of 2-bromopropiophenone as a test substrate, it was demonstrated that the active sites in [Cu3(btc)2] are hard Lewis acids. Catalyst stability, re-usability, and heterogeneity are critically assessed.
Chemistry 10/2006; 12(28):7353-63. · 5.93 Impact Factor
