Synthesis and gas permeation properties of silicalite-1 zeolite membrane

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Absolute integrated SAXS measurements during the crystallization of linear polyethylene

Absolute intensity measurements of a dynamic small-angle x-ray scattering from a linear polyethylene were carried out during polymer crystallization from melt in a temperature range of 113.5° to 124.5°C. The mean-square modulation of the electron density over the irradiated volume was evaluated and the feasibility of dynamic experimentation for crystallization kinetic analysis was established. The results provide an absolute value of mass density of the amorphous phase of a semicrystalline polymer at the crystallization temperature.     

Effect of aging temperature of alkaline aluminosilicate and silicate gels on the kinetics of crystallization of zeolite ZSM-5 and silicalite-1

The temperature dependences of nucleation of zeolite ZSM-5 and silicalite-I pass through extrema in the range from 110 °C to 120 °C. Despite having the same crystalline structures, zeolite ZSM-5 has a maximum and silicalite-1 has a minimum of nucleation in the temperature range mentioned. A method for preparation of single crystals of silicalite-1 up to 150 m in size has been developed. The comparison of the curves of the temperature dependences of nucleation for zeolites Na-X, Na-A, and ZSM-5 shows that the positions of the maxima on these curves are determined by the type of the crystal structure of zeolite.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1091–1095, May, 1996.     

Adsorption of liquid mixtures on silicalite-1 zeolite: a density-bottle method

A technique that measures the effective density of a zeolite after adsorption from the liquid phase was developed to measure the absolute amounts of liquid mixtures adsorbed on zeolites without using a nonadsorbing solvent. Since the fugacities of the adsorbing components in solution can be dramatically different with or without the addition of a nonadsorbing solvent, this technique measures mixture isotherms that can be used for analyzing pervaporation through zeolite membranes. A nonideal solution, methanol/acetone, was used as an example to show that its adsorption isotherms on silicalite-1 zeolite at 294 K differ dramatically from those measured with the nonadsorbing solvent method. The methanol/acetone fugacity ratio is different for the two methods because of different concentrations in the liquid phase. Methanol preferentially adsorbs on silicalite-1 at low methanol concentrations and acetone preferentially adsorbs at high methanol concentrations. The density bottle method was used to show that n-hexane preferentially adsorbs from n-hexane/3-methylpentane liquid mixtures, and at high n-hexane concentrations, essentially no 3-methylpentane adsorbs, as has been predicted previously by simulations. A larger molecule, 2,2-dimethylbutane, adsorbed so slowly at 294 K that silicalite had only 16% of saturation coverage after 370 h, but it was saturated after 1650 h; at 423 K, saturation was obtained in less than 24 h.     

Silicalite-1修饰的HY型分子筛及其对纤维素水解的催化性能

采用silicalite-1对HY型分子筛进行修饰,得到具有核壳结构的复合分子筛HY/silicalite-1。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、N2的吸附-脱附及吡啶吸附红外(Py-FTIR)等手段对不同晶化时间合成的HY/silicalite-1复合分子筛进行了表征,研究了复合分子筛对纤维素水解的催化性能。结果表明,晶化时间直接影响复合分子筛的晶体生长规律和两组分的相对含量,最佳晶化时间为16-24 h,所得到的复合分子筛外貌呈核壳结构,silicalite-1附晶生长在HY型分子筛的表面;随着晶化时间的延长,复合分子筛的表面由胶浊状变为光滑,最终变为鳞片状;其B酸量先减少后增加,而L酸量则先增加后减少。其中,晶化时间为24 h的HY/silicalite-1复合分子筛B酸量最大,L酸量最小,对纤维素水解反应具有良好的催化性能,葡萄糖收率由HY型分子筛催化获得的28.0%大幅提高至45.8%。     

堇青石栽体表面ilicalite-1沸石膜的合成与表征

本文首次采用堇青石为载体,用水热合成方法,制备了致密的高硅MFI沸石膜,并对其结构、成分以及气体渗透性质进行表征。     

Water condensation in hydrophobic silicalite-1 zeolite: a molecular simulation study

We report grand canonical Monte Carlo simulations of the gas and liquid phase adsorption of water in silicalite-1 zeolite. Simple but effective models and simulation methods, found useful for studying gas adsorption in nanoporous materials, have been extended to describe the intrusion/extrusion cycle of water in this hydrophobic solid. The picture of water confined to hydrophobic spaces of nanoscopic dimensions that emerges from this study is one of a strongly depleted and highly inhomogeneous fluid.     

Titanium silicalite-1 zeolite microparticles for enzymeless H2O2 detection

In this communication, we demonstrate for the first time that titanium silicalite-1 zeolite microparticles (TSZMs) can effectively catalyze the reduction of H(2)O(2), leading to an enzymeless H(2)O(2) sensor with a linear detection range from 100 μM to 40 mM (r = 0.994) and a detection limit of 0.5 μM at a signal-to-noise ratio of 3.     

Preparation and catalytic activity of titanium silicalite-1 zeolite membrane with TPABr as template

The preparation of the supported titanium silicalite-1 (TS-1) zeolite membrane with inexpensive tetrapropylammonium bromide (TPABr)/weak base synthesis system was studied by three methods, and the catalytic activity of the obtained TS-1 zeolite membrane was evaluated with the oxidation of 2-propanol (IPA) under pervaporation condition. It was found that TS-1 zeolite membrane could be successfully prepared with “seeding” or “seeding in situ” method, but could not be achieved with “in situ” method. Adding a little amount of promoter ions of PO₄³⁻ into the synthesis gel was of benefit to the catalytic activity of the prepared TS-1 zeolite membrane, but had no obvious effect on the membrane layer formation on the mullite porous support. For “seeding” method, the membrane prepared with the synthesis gel having molar composition of SiO₂:0.1TPABr:0.9Et₂NH:0.03TiO₂:80H₂O:0.06H₃PO₄ at 150 °C for 48 h showed the highest oxidation conversion of IPA of 72% accompanied by a flux of 0.35 kg/m² h. Further more, much higher IPA oxidation conversion of 76% accompanied by a flux of 0.65 kg/m² h was obtained for the TS-1 zeolite membrane prepared with the same synthesis gel by “seeding in situ” method at 150 °C for 72 h.     

Temperature-programmed crystallization of zeolite A

Crystallization rates of zeolite A were studied in a constant-temperature mode and a temperature-programmed mode. The crystallization rate in the constant-temperature mode was examined using the engineering reaction model. Activation energy for crystal growth was determined to be 32.8 kJ/mol. The crystallization curves in the temperature-programmed mode could be simulated by using the rate constants and the fractions of soluble species determined from the constant-temperature mode experiments.     

Aggregative growth of silicalite-1

Precursor silica nanoparticles can evolve to silicalite-1 crystals under hydrothermal conditions in the presence of tetrapropylammonium (TPA) cations. It has been proposed that in relatively dilute sols of silica, TPA, water, and ethanol, silicalite-1 growth is preceded by precursor nanoparticle evolution and then occurs by oriented aggregation. Here, we present a study of silicalite-1 crystallization in more concentrated mixtures and propose that growth follows a path similar to that taken in the dilute system. Small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and high-resolution transmission electron microscopy (HRTEM) were used to measure nanoparticle size and to monitor zeolite nucleation and early-stage crystal development. The precursor silica nanoparticles, present in the clear sols prior to crystal formation, were characterized using two SAXS instruments, and the influence of interparticle interactions is discussed. In addition, SAXS was used to detect the onset of secondary particle formation, and HRTEM was used to characterize their structure and morphology. Cryo-TEM allowed for in situ visual observation of the nanoparticle population. Combined results are consistent with growth by aggregation of silica nanoparticles and of the larger secondary crystallites. Finally, a unique intergrowth structure that was formed during the more advanced growth stages is reported, lending additional support for the proposal of aggregative growth.     

In situ synchrotron SAXS/WAXD studies during melt spinning of modified carbon nanofiber and isotactic polypropylene nanocomposite

The structural development of a nanocomposite, containing 95 wt% isotactic polypropylene (iPP) and 5 wt% modified carbon nanofiber (MCNF), during fiber spinning was investigated by in situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. The modification of carbon nanofibers (CNFs) was accomplished by a chemical surface treatment using in situ polymerization of olefin segments to enhance its compatibility with iPP, where the iPP/MCNF nanocomposite was prepared by twostep blending to ensure the dispersion of MCNF. X-ray results showed that at low spin-draw ratios, the iPP/MCNF nanocomposite fiber exhibited much higher iPP crystalline orientation than the control iPP fiber. At higher spin-draw ratios, the crystalline orientation of the nanocomposite fiber and that of the pure iPP fiber was about the same. The crystallinity of the composite fiber was higher than that of the control iPP fiber, indicating the nucleating effect of the modified carbon nanofibers. The nanocomposite fiber also showed larger long periods at low spin-draw ratios. Measurements of mechanical properties indicated that the nanocomposite fiber with 5 wt% MCNF had much higher tensile strength, modulus and longer elongation to break. The mechanical enhancement can be attributed to the dispersion of MCNF in the matrix, which was confirmed by SEM results.Dedicated to Prof. E D. Fischer on his 75th birthday.     

Measuring true electromechanical strain of electroactive thermoplastic elastomer gels using synchrotron SAXS

The true electric actuation thickness strain of poly (styrene‐b‐ethylbutylene‐b‐styrene) (SEBS) gel was measured using an in situ synchrotron SAXS. The thermoplastic elastomer SEBS gel was microphase‐separated to form a disordered styrene micelle nanostructure in an oil‐swollen ethylbutylene matrix. The SEBS gel showed reversible cyclic load–unload compression behavior without permanent residual strain. The electromechanical strain of the SEBS gel with carbon paste electrodes could be evaluated by means of a nanostructure dimensional change traced by using the in situ synchrotron SAXS during actuation. The strain measured with SAXS was compared with the strain measured using conventional laser displacement sensor systems. The optical laser sensor method was likely to overestimate the thickness strain due to the bending movement of the dielectric elastomer. To our knowledge, the thickness strain value measured by the synchrotron SAXS is the closest to the true strain ever measured in the field of dielectric elastomer studies, because the nanostructure dimensional change depends on the thickness dimension change, not on the translational movement like the bending motion. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Ultra-small PtNi bimetallic encapsulated in silicalite-1 zeolite with fine-tuned surface acidity for selective conversion of levulinic acid

Exploration of levulinic acid (LA) hydrogenation to γ-valerolactone (GVL) contributes to the conversion from carbohydrates to valuable fuels and chemicals. Here, we obtained a series of ultra-small PtNix bimetallic composite catalysts encapsulated in silicalite-1 zeolite (S-1) via a one-pot synthesis strategy protected by tetra(p-carboxyphenyl)porphyrin (TCPP) ligands. The catalytic results showed that PtNi₃@S-1 (TCPP) exhibited the most active catalytic performance (95.7% LA conversion and 93.8% GVL selectivity) under optimized conditions. The characterization results indicate that ligand modification and bimetallic synergy play an important role in enhancing the catalytic activity. The introduction of TCPP provides a guarantee for the homogeneous encapsulation of PtNi₃ in S-1 zeolite at sub-nanometer size. The electronic interaction of PtNi bimetallic, high dispersibility of active components, improved surface acidity and excellent stability co-contribute to the satisfactory hydrogenation activity.     

Adsorption of lipids on silicalite-1

Russian Journal of Physical Chemistry A - The adsorption of egg lecithin and cholesterol from chloroform solutions onto silicalite-1 (hydrophobic silica with MFI zeolite structure) is investigated....     

SAXS study on the structure and crystallization of amorphous metallic alloys

The change in structure of several amorphous alloys as Fe-P-C, Fe-B and Pd-Au-Si alloys during isothermal ageing was examined using small angle X-ray scattering technique as well as transmission electron microscopy. The SAXS intensity was related to two different types of scattering sources depending on ageing period and temperature. As-splatted amorphous alloys and the specimens aged for short period at relatively low temperature, where specimens remained in amorphous state, showed a weak and spreaded SAXS intensity. This indicates an existence of electron density fluctuation in amorphous phase. The dimension of their scattering regions was estimated to be 1.8 to 2.4 nm for Fe-P-C alloys, and 1.2 to 0.8 rim. for Fe-B alloys, respectively, by analysing the electron density-density correlation function derived from observed SAXS intensity. The origin has been discussed based on one dimensional model. A compositional fluctuation was made clear to occur in fine scale of about 1 nm in amorphous Fe-B and Fe-P-C alloys. When the alloys were aged for longer period below their crystallization temperatures, fine crystalline particles precipitate; those are a two phase lamella structure of Fe₃P and-Fe for a Fe₈₃P₁₀C₇ alloy, an Ferich single phase for Fe₈₃B₁₇ alloy, and a Pd-rich single phase for Pd₇₆Au₆Si₁₈8 alloy, respectively. Their size and structure were determined from the analysis of SAXS data and TEM observation.     

Newly developed ab initio fitted potentials for molecular dynamics simulations of n-pentane in the zeolite silicalite-1

Ab initio fitted potentials representing n-pentane/n-pentane and n-pentane/silicalite-1 interactions were newly developed at the second-order Møller-Plesset perturbation (MP2) level with the 6-31G* basis set. Characteristics of the functions were illustrated in comparison with available force field models. They were, then, applied for the molecular dynamics simulation of n-pentane in silicalite-1. The diffusion coefficients are in satisfactory agreement with the results of PFG-NMR experiments. The effect of the box size was also examined. It was found that the components of the diffusion tensor are very sensitive to this parameter. The structure of the n-pentane in the silicalite-1 pore was analyzed in terms of radial distribution functions. The first peak at 4.1 Å indicates the optimal diffusion route of the n-pentane along the central line of the channel of the silicalite-1.     

Simulation of SAXS patterns of hexa-n-alkoxy-2,3,6,7,10,11-triphenylene mesophase

Small-angle X-ray scattering (SAXS) experiments and molecular dynamic modelling of the mesomorphic organisation of hexa-n-pentoxy-2,3,6,7,10,11-triphenylene are reported. Simulated SAXS patterns extracted from molecular dynamic simulations account for the fact that despite a perfect organisation of the columns in a 2D hexagonal array, in most case, SAXS patterns show only the fundamental diffraction peak with a limited number of higher order reflections.     

Sorption of alkanediols by silicalite-1

Isotherms for the sorption of linear alkanediols HO(CH₂) _n OH (n = 2, 4, 6, 8) from aqueous solution by silicalite-1 at 25° are reported.