No abstract

The objective of this work was to study the adsorption and separation of the most important families of hydrocarbon compounds on metal-organic frameworks (MOFs), in comparison with zeolites. For this purpose, we have selected four probe molecules, each of them representing one of these families, i.e., o- and p-xylene as aromatics, 1-octene as an alkene, and n-octane as an alkane. The separation of these four molecules was studied by binary breakthrough experiments. To represent the large diversity of MOF structures, the experiments were carried out with (i) two MOFs with coordinatively unsaturated metal sites (CUS), i.e., Cu-btc (HKUST-1) and CPO-27-Ni, (ii) a MOF with an anionic framework and extraframework cations, i.e. RHO-ZMOF, and (iii) two rather apolar zeolitic imidazolate framework (ZIF) materials with different pore sizes, i.e. ZIF-8 and ZIF-76. Zeolite NaY and zeolite β were used as polar and apolar reference adsorbents, respectively. The results can be briefly summarized as follows: ZIFs (not carrying any polar functional groups) behave like apolar adsorbents and exhibit very interesting and unexpected molecular sieving properties. CUS-MOFs behave like polar adsorbents but show the specificity of preferring alkenes over aromatics. This feature is rationalized thanks to DFT+D calculations. MOFs with extraframework cations behave like polar (cationic) zeolites.

The separation of paraffin isomers is a very important topic in the petrochemical industry. Zeolite 5A is industrially used to sieve alkane isomers, but its pore size does not allow the separation of monobranched and dibranched alkanes by a kinetic mechanism. In this publication, we compare three ZIF materials in the separation of C6-paraffin isomers: ZIF-8, ZIF-76, and a new material called IM-22. The performance of the materials is evaluated by a breakthrough curve of binary mixtures of n-hexane, 3-methylpentane, and 2,2-dimethylbutane. We show that ZIF-8 is a very attractive alternative to zeolite 5A because it exhibits a high (kinetic) selectivity for the adsorption of linear alkanes and at the same time a high adsorption capacity. The new material IM-22, a ZIF with CHA topology, seems to be particularly suited for the separation of mono-and dibranched paraffin isomers.

Porous solids [1] usually find applications in the areas of ionexchange, separation, and catalysis. The recent discovery of new materials based upon transition metal ions [2] opens the possibility of making open frameworks that exhibit also some of the remarkable electronic properties of condensed transition metal compounds (ferro-and ferrimagnetism, metalsemiconductor transitions, ferroelectricity, combined ionic/ electrical conductivity). Up to now, in the field of magnetism, the major limitation for producing porous solids with high ordering temperatures came from the structure itself. Indeed, most of the porous compounds are built from metallic clusters linked by diamagnetic linkers (phosphates, arsenates, silicates, aliphatic chains) which prevent strong, long-range interactions. To date, the highest Ne ¬ el temperatures were observed for the purely inorganic porous skeleton of ULM-3 [3] (37 K) and for the hybrid solid HKUST-1 [4] (75 K).To overcome this difficulty, our design strategy is to link chains of corner-sharing transition metal octahedra (which favor strong, long-range superexchange coupling) by rigid organic linkers containing delocalized p electrons for the three-dimensional transmission of the interactions. The use of such linkers was mainly developed by the groups of Yaghi and O×Keeffe, [5a] Zaworotko, [5b] and Kitagawa [5c] for metal-organic frameworks with modulable very large pores.As an example of our design principle, we describe here the synthesis, structure, magnetic and sorption properties of a large-pore, flexible, open framework (MIL-47) that is antiferromagnetic below 95 K.To implement this design, we used the hydrothermal reaction (teflon-lined steel autoclave Parr, four days, 473 K, autogenous pressure, filling rate: 50 %) of either a mixture of VCl 3 , terephthalic acid, and desionized water (molar ratio 1:0.25:100), which only provides homogeneous pure powders, or of vanadium metal, terephthalic acid, hydrofluorhydric acid, and water (molar ratio 1:0.25:2:250) when crystals are needed. In both cases, the pH value remains 1 throughout the synthesis and the yield is close to 15 %. The resulting light yellow product, (hereafter labeled MIL-47as), which is stable in air, is formulated V III (OH){O 2 C-C 6 H 4 -CO 2 } ¥ x(HO 2 C-C 6 H 4 -CO 2 H) (x $ 0.75) on the basis of elemental analysis (calcd: C 47.1, V 14.3; found: C 46.87, V 13.79;). Both thermodiffractometry and thermal analyses (TGA2050 TA apparatus, O 2 flow, heating rate 2 K min À1 ) show (Figure 1 a) a decomposition of MIL-47as in two steps between 300 and 420 8C. The first weight loss (exp.: 32.3 %, calcd: 34.92 % for proteins suggest that such a universal inhibitor design could potentially be effective against several different viruses. [18] [1] For a recent review, see A. G. Cochran, Chem.