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Abstract: The present work describes the adsorption and separation of xylene isomers by ZIF-8. Although the formal pore diameter of ZIF-8 is much smaller than the molecular diameter of the xylene isomers, ZIF-8 is able to separate the isomers by molecular sieving. A structural study indicates that the diffusion of the xylenes into the pore structure of ZIF-8 happens via a transitory deformation of the pore aperture which is based on a tilt of the imidazolate linkers, followed by a return to the initial conformation. The rate of adsorption depends on the size of the isomer, i.e. it decreases from para- to meta- and to ortho-xylene. The separation of the xylene isomers is good in the gas phase. In liquid phase breakthrough experiments, the quality of the separation is deteriorated. Moreover, as expected for a separation based on molecular sieving, para-xylene cannot be well separated from ethyl-benzene. [Copyright &y& Elsevier]

Abstract: ZIF-76, Zn(Im) x (5-ClbIm) y (Im=imidazolate, 5-ClbIm=5-chlorobenzimidazolate), is, among the known ZIF structures, one of the few materials that combine a relatively large pore aperture with a large pore volume. Moreover, it is thermally stable up to 400°C and can be stored under ambient atmosphere without undergoing a measurable degradation. ZIF-76, therefore, appears to be an interesting material for applications in adsorption and separation. The published synthesis protocol leads to very low yields and is, thus, not applicable on a larger scale . In this work, we have succeeded in preparing ZIF-76 in suitable yields by changing the solvent and adding NaOH to the synthesis mixture. The addition of the base increases the yield and leads to smaller crystal sizes, by favoring nucleation over crystal growth. By using the same synthesis strategy, four new isomorphs of ZIF-76 were obtained, with different substituents on the benzimidazole ligand (Me, Br and NO2) and different metal sources (Co and Zn). All the samples were tested in the adsorption and separation of CO2/CH4 in order to highlight the influence of the linker and of the metal center on the adsorption/separation properties. [Copyright &y& Elsevier]

Highlights: [•] MIL-53(Al) reacts with water under reflux yielding H2BDC and γ-AlO(OH). [•] Maximum reaction degree is 20%. [•] H2BDC molecules are occluded in the pores. [•] Sheets of γ-AlO(OH) form a shell around the particles. [•] Reflux in water can be used to modify the surface chemistry of MIL-53(Al). [ABSTRACT FROM AUTHOR]

Adsorptive separation of propylene (C 3 H 6) and propane (C 3 H 8) may represent an energy-efficient alternative to conventional cryogenic distillation. In this perspective, a set of zeolitic adsorbents of LTA type structure (pure-silica zeolite (Si-LTA) and cation- (Na+, 33% of Li+, 50% of Mg2+ and 50% of Ca2+) containing zeolites) were prepared, then characterized using various techniques such as PXRD, gas adsorption measurement, TGA, XRF, SEM and EDX mapping. Thanks to an in-house manometric dosing setup coupled with a Tian-Calvet type microcalorimeter, the pure gas adsorption isotherms and their corresponding differential enthalpies of adsorption were measured at 303 K and for pressures up to 5 bar. To fit those adsorption data, the dual-site Langmuir was selected as the best fit model, and by using the Ideal Adsorbed Solution Theory (IAST), thermodynamic selectivities were determined. The mass transfer constants were also estimated by fitting, separately, the Linear Driving Force (LDF) and isothermal micropore diffusion models to adsorption kinetic curves, thus allowing kinetic type selectivities to be calculated. The combination of those selectivities reveals that the thermodynamic separation of C 3 H 6 from C 3 H 8 is highly favorable on CaNa-LTA, followed by its MgNa-LTA counterpart with IAST selectivities around 15 and 5, respectively. On the other hand, the monovalent cationic zeolites (i.e., Na- and LiNa-LTA) show a predominance of steric effects. Also, except for Si-LTA which shows a moderate kinetic separation, the studied materials are potential candidates, in the following order CaNa- > MgNa- > LiNa- > Na-LTA, for the separation of C 3 H 6 from C 3 H 8 by adsorption-based technologies. [Display omitted] • Adsorption enthalpies of C3 on LTA zeolites have been measured by microcalorimetry. • LTA zeolite with Li+ and Na+ are able to kinetically separate C3 mixture. • LTA with Ca2+ and Mg2+ are promising candidates for thermodynamic separation. • Ca2+ cations effectively improve the IAST selectivity 3 times with respect to Mg2+. [ABSTRACT FROM AUTHOR]

Water adsorption in the large pore ( lp_empty ) form of Ga-MIL-53 was studied by TGA, DSC and in situ XRD and FTIR at 298 K. The large pore form can be stabilized at room temperature after activation under vacuum at 553 K. The isotherm of water adsorption in this large pore form (pore dimensions: 1.67 × 1.33 nm) is very similar to that measured on the narrow pore ( np_empty ) form (pore dimensions: 1.97 × 0.76 nm). Such a similarity is rather unusual given that the pore sizes of these two phases are very different. In order to understand the origin of this effect in situ XRD and FTIR measurements were particularly helpful. It was found that the adsorption of even small amount of water (0.05 mol per Ga atom at 0.2 hPa) in the large pore form of Ga-MIL-53 transforms ca. 50% of the solid into a narrow pore int phase, which is assumed to be present as a shell around the lp_empty core. Additional water molecules adsorbed at higher pressures do not interact with the parent lp_empty phase but with the narrow pore int phase. The phase transformations were confirmed by FTIR revealing significant band displacements in the corresponding pressure ranges. Such easy pore shrinking which occurs at very low water pressure (<0.2 hPa) can have undesirable consequences in working conditions, as for example in separation adsorption processes, because the large pore structure of Ga-MIL-53 can be preserved only under anhydrous conditions. [ABSTRACT FROM AUTHOR]

The present study demonstrates an optimized procedure for mass production of EMT-type structure zeolite. The introduction of triethanolamine (TEA) in the synthesis gel leads to the formation of larger and agglomerated nanocrystals. The obtained particles can be easily recovered from the reaction medium by filtration and washing without the use of high speed centrifugation. This simple approach paves a new way for energy-efficient synthesis of nanoporous materials for potential industrial applications. [ABSTRACT FROM AUTHOR]

The amino modified MIL-68(In), hereafter denoted by MIL-68(In)_NH2, has been obtained by self-assembling from 2-amino-terephthalic acid and indium nitrate hydrate. The characterization of the modified material based on powder X-ray diffraction analysis, IR spectroscopy, 1H NMR spectroscopy and TG analysis demonstrates that this porous coordination network possesses the Kagomé topology of MIL-68(In) with amino modified pores walls. The Brunauer–Emmett–Teller surface area of 1230±24m2 g−1 for MIL-68(In)_NH2 compared to 1028±29m2 g−1 for MIL-68(In) exhibits an surface area improvement of approximate 200m2 g−1 within MIL-68(In)_NH2. Moreover, for both hybrids, the hydrogen and carbon dioxide sorption properties have been studied at 77K and 87K, and at 273K and 298K, respectively. The comparison of the corresponding results of MIL-68(In) shows that the presence of amino group can effectively enhance the adsorption enthalpy of H2 and CO2, whereas, slightly effect on the integral sorption amount. Besides, to our knowledge, it is the first time that the CO2 adsorption of MIL-68(In) sample are reported. [ABSTRACT FROM AUTHOR]

Abstract: One way to obtain new materials is to exploit the in situ generation of the structure-directing agent. By this synthetic route, solvents or precursors of the templates are introduced into the starting mixtures, and during the synthesis, they partly decompose into molecules that act as templates. This paper deals with the synthesis of a fluorogallophosphate with a new template precursor, the N-formylmorpholine. This compound, used as main solvent, is unstable in acidic media. At high temperature it decomposes and generates in situ the morpholine molecules. We report the structure of a two-dimensional fluorogallophosphate named Mu-38 structurally related to ULM-9. This compound Ga3P3O12F3[C4H10NO]3 (Z =4) consists of anionic inorganic layers containing single four rings units linked and charge-balanced by protonated morpholine. It was also characterized by powder XRD, SEM, elemental and thermal analyses, and solid state NMR spectroscopy (13C, 19F and 31P MAS and 31P CP MAS experiments). [Copyright &y& Elsevier]