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Abstract: A zeolite beta–silicalite-1 composite was prepared by growing polycrystalline silicalite-1 shells on single micron-sized zeolite beta crystals. The obtained core–shell material was employed for the separation of hexane isomers. Gravimetric uptake measurements revealed that the silicalite-1 shell acted as a membrane that controlled the transport to zeolite beta core. The positive impact of the silicalite-1 membrane on the separation of mono- and di-branched hexane isomers was confirmed by breakthrough experiments. The core–shell composite material allowed more selective separation of mono- and di-branched isomers than either of its components alone and had a significantly higher adsorption capacity than silicalite-1. [Copyright &y& Elsevier]

Abstract: Benzene and four trisubstituted aromatic compounds were used as swelling agents for mixed hexadecyl- and dodecyltrimethylammonium micelles. These micelles served as templates for the synthesis of mesoporous M41S materials. By varying the amount and the nature of the aromatic swelling agent, M41S materials with any pore diameter between 3 and 11nm could be synthesized. All materials exhibited specific surface areas around 1000m2/g and large specific pore volumes as it is characteristic for the M41S family. Phases with layered, rod-like, and globular building units were obtained by varying the nature and/or the amount of aromatic swelling agent. A detailed analysis of the trends showed that the hydrophobicity of the swelling agents determines the size and shape of the pores: with the more hydrophobic swelling agents smaller pores with higher curvature are obtained. [Copyright &y& Elsevier]

Abstract: Mesoporous materials were synthesized from solutions containing ZSM-5 precursors in the presence of a micellar template (CTACl). The effect of different parameters like aluminum content, aging conditions and hydrothermal treatment conditions on the properties of the final materials was investigated by dynamic light scattering (DLS), N2 physisorption, XRD, 27Al MAS-NMR, TEM and IR. In addition two catalytic test reactions (cracking of isopropylbenzene and 1,3,5-triisopropylbenzene) and acidity measurements via pyridine adsorption were carried out. We observed a transition of the initially formed mesoporous structure containing protozeolitic seeds to a zeolitic phase during hydrothermal treatment. The rate of zeolitization strongly depended on the conditions of the aging period and on the composition of the synthesis solution: the more protozeolitic seeds were formed during the aging procedure the faster the zeolitization. Catalytic test reactions and acidity measurements showed that the XRD amorphous materials with protozeolitic seeds in the mesoporous structure are more active and more acidic than mesoporous materials prepared without ZSM-5 precursors, but far less active and acidic than zeolites. A combination of high activity and accessibility of most active sites was found for samples containing small zeolite crystals. [Copyright &y& Elsevier]

Abstract: The surface of mesoporous M41S silica material was functionalized with 3-aminopropyl and methyl groups and with mixtures of both. The ratio of the two groups on the silica surface could be adjusted by changing the molar ratio of the corresponding alkoxysilanes in the reaction mixture. The fraction of 3-aminopropyl on the surface was always larger than in the functionalization reaction mixture. Moreover, functionalization with the 3-aminopropyl group or with mixtures of the 3-aminopropyl and methyl groups led to higher molar coverages of the silica surface than functionalization with the methyl group alone. One reason for these effects is that the amino group base-catalyzes the hydrolysis of the alkoxysilanes and thereby enhances the reaction of the silanes with the silica surface. The 3-aminopropyl/methyl—functionalized materials showed a very high stability against hydrolysis in boiling water because the siloxane bonds of the silica framework were protected by the organic moieties. [Copyright &y& Elsevier]

The effect of various acid treatments and of two different sodium silicate sources on the pore characteristics and the hydrothermal stability of pure silica MCM-41 was investigated. The best material was obtained by addition of acetic acid after 24 h of the synthesis, which lasted in total 96 h at 100 °C. There was a correlation between the pore characteristics and the hydrothermal stability. The material with the best pore characteristics as revealed by nitrogen adsorption and XRD also showed the best hydrothermal stability during steaming and refluxing in water. The relative loss of pore volume after 6 h of steaming at 500 °C was only 15%. The positive effect of the acid treatment on the pore characteristics and the hydrothermal stability is mechanistically explained by two factors, (i) the shift of the equilibrium of silica condensation and (ii) the decrease in electrostatic repulsion among the negatively charged silicate species in the alkaline synthesis gel. In the comparison of the two silica precursors, better results were obtained using the sodium silicate solution containing larger silicate species. [Copyright &y& Elsevier]

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: The crystal chemistry of divalent metal N,N′-piperazinebis(methylenephosphonates) of the STA-12 family, (M2(H2O)2(O3PCH2NC4H8NCH2PO3)·xH2O, M=Mg, Mn, Fe, Co, Ni) is compared. The different metal analogues are isostructural in the hydrated forms, possessing symmetry, but their reversible dehydration behaviour and resultant porosity are strongly dependent on the metal cation. Whereas the Co and Ni forms change symmetry to triclinic upon dehydration, giving permanent porosity to N2 of 0.14cm3 g−1 and 0.27cm3 g−1, respectively, the Mn and Fe forms remain rhombohedral but exhibit a strong decrease in unit cell volume (e.g. 23% for STA-12(Mn)). Structure determination of dehydrated STA-12(Mn) indicates a topotactic transformation with a change in coordination of the phosphonate O atoms. Negligible permanent porosity is observed in either dehydrated STA-12(Mn) or (Fe), suggesting the presence of non-crystallographic pore blocking. Dehydration of STA-12(Mg) results in loss of some long range order, preventing structural determination of the fully dehydrated form, but does give appreciable permanent porosity for N2 of 0.20cm3 g−1. Infrared spectroscopy (and for STA-12(Mg) solid-state NMR spectroscopy) have been used to follow the changes upon dehydration. Applications of the most porous and stable STA-12 structure, the Ni form, have also been investigated. CO2 adsorption selectivity over CH4 and CO has been measured via analysis of breakthrough curves, and a Porous Layer Open Tubular (PLOT) gas chromatographic column has been prepared and used to separate a mixture of low molecular weight alkanes. [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]

The texture of a series of dealuminated macrocrystalline beta zeolites has been investigated by N2 physisorption, transmission electron microscopy, and electron diffraction. Hydrothermal dealumination creates a secondary mesoporous system in zeolite BEA. N2 physisorption together with DFT calculations indicated the presence of pores with an estimated size of 2–4 nm after steaming. After subsequent leaching, TEM revealed the newly formed cylindrical mesopores. As determined by electron diffraction, the new porous network consists of pores lying in the (0 0 1) plane. [Copyright &y& Elsevier]