The conditions of static in-situ hydrothermal synthesis were optimized to prepare crystalline, pure phase and template-free small pore zeolite SSZ-16 (AFX) particles. The type of silica source and prolonged ageing process at an elevated temperature were decisive in obtaining pure phase zeolite SSZ-16 particles under static conditions and conventional heating. Colloidal and fumed silica-based synthesis mixtures were successful in forming the zeolite SSZ-16. The zeolite particle size was reduced from 46 to 5 mu m when the fumed silica was replaced by colloidal silica. Uniform, fine-grained and fully crystalline zeolite SSZ-16 particles were synthesized only from the colloidal silica-based mixtures that were aged at 80 degrees C for 7 days. The elevated temperature of the ageing stage is supposed to promote nucleation of viable nuclei leading to the reduction of the induction period. The two cycle calcination procedure with maximal temperature of 550 degrees C, ensured the removal of template molecules from the bulk phase of zeolite SSZ-16 particles. Carbonaceous residua were observed in zeolite subsurface region and mainly in the core shell morphology of zeolite SSZ-16 particles. The phase purity of zeolite SSZ-16 particles was checked by XRD and sorption properties were determined by N-2 adsorption at -196 degrees C. Zeolite SSZ-16 particles showed the micropore volume of 0.24 cm(3)/g and BET surface area of 496 m(2)/g. (C) 2016 Elsevier Inc. All rights reserved.

In this work, the synthesis of self-supported layers over mercury was carried out. Influence of the amount of water, TPA+, OH− and Na+ in the precursor gel was investigated for this kind of synthesis. Layers were characterized by X-ray diffraction to study their crystallographic structure, scanning electron microscopy to determine their thickness and crystal properties, and mercury porosimetry for the determination of layer density.

Topochemical and catalytic effects of ZSM-5 zeolite framework in the course of thermal degradation of tetrapropyl ammonium (TPA+) template upon calcination under oxidative (air) and inert (nitrogen, N2) atmosphere was analyzed using elemental analysis, X-ray Photoelectron Spectroscopy (XPS) and absorption UV–Vis–NIR spectroscopy. It has been demonstrated that template residues were selectively removed from the interior of the crystals. The concentration of (N (C)-containing template species was ⩽1 atom per unit cell (u.c.)) by prolonged (24h) calcination in air already at temperature Tmax=310°C (N-containing template species) and Tmax=330°C (C-containing template species). Calcination in N2 requires temperatures higher by about 20°C. The surface region of ZSM-5 crystals contained, however, a substantial amount of template residua (20–30% of N-containing and ∼60% of C-containing species) even at Tmax=430°C. This effect is associated with conversion of propylene, originating from TPA+ degradation, into low volatile products by their dehydrogenation on acidic centers and defect sites of ZSM-5. The dehydrogenation reaction was enhanced under oxidative conditions. The volatility of carbonaceous and N-containing residues was further reduced by their strong interaction with defect sites of ZSM-5.

Zeolite MFI crystal layers were grown on different α-alumina supports. Permeation and separation characteristics of selected zeolite MFI composite membranes were measured for the system of butane isomers. Flux, permeation and separation factors were measured as a function of feed pressure, temperature and feeding amount of butane isomers. The experiments, based on Wicke–Kallenbach method, were carried out using steady-state membrane apparatus MEMFIS. The observed fluxes and permeances of n-butane were higher in comparison with isobutane for all membranes. The separation factors exhibited the maxima in the dependence on temperature and decreased with increasing feed pressure. It follows from the comparison of single component and binary mixture experimental data that n-butane permeance was strongly reduced by the presence of isobutane as a co-permeating component in the binary mixture. However, isobutane was practically not influenced by the presence of n-butane. Long-term continuous membrane separation resulted in gradual decrease of butane isomers flux and corresponding separation factor. The flux decrease was more pronounced for isobutane. Reactivation of the membranes showed a slight increase of butane isomers flux but continuous decrease of separation factor.

In this contribution the issue of the stochastic reconstruction of particulate media from 2D backscatter SEM images is addressed with particular reference to pore space connectivity. The reconstruction of porous bodies in 2D or 3D space was achieved by using a simulated annealing technique. Two constraints were found to be necessary for the successful reconstruction of well connected pore space: the two-point probability function, and the lineal-path function for the solid phase. Surprisingly, the most commonly used method of reconstruction (common method), consisting of a similar application of both the two-point probability function and the lineal-path function for the void phase, resulted in microstructures characterized by poor pore space connectivity, and by artificial patterns. Since it is desirable to employ the maximum possible number of microstructural descriptors (i.e. to use the lineal-path function for the void phase), we propose a new method of reconstruction. The influence of the lineal-path function for the void phase was suppressed during the initial stages of 2D reconstruction, thereby creating the possibility of obtaining microstructures whose two-point cluster functions match the experimentally measured functions. The effect of the lineal-path function for the void phase on the course of the reconstruction was adjusted by modifying two parameters of the reconstruction procedure. It was tacitly assumed that the parameters adjusted during 2D reconstruction had the same influence on the formation of 3D microstructures. Therefore, the experimental two-point cluster function, extracted from the 2D images, was only used indirectly during 3D reconstruction. 3D replicas obtained using our new method exhibited significantly better pore space connectivity and were more penetrable than porous bodies reconstructed using the common method.

A pore network model is presented to predict permeability and diffusivity in porous bodies with a relatively high porosity. The model application is exemplified on a macroporous sample of α-alumina with the porosity of ≈0.4. The network model is constructed on the basis of proximity of the computed data on its total porosity, pore-size function, and simulated mercury intrusion curve to the respective experimental data. The experiment related pore-size function is extracted from a 3-D stochastic replica of the α-alumina sample obtained by stochastic reconstruction. The reconstruction technique employs morphological information based on a set of 2-D cuts through the porous medium. The only free parameter in the network construction is connectivity. The impact of the connectivity adjustment on the transport properties is studied. If the calculated mercury intrusion curve is forced to fit the experimental one, changes in connectivity are counterbalanced by the presence of slightly wider or narrower throats in the network. This compensation effect decreases the span of calculated values of permeability and diffusivity, which agree well with experiment.

Immobilization of ethylene in the channel system of HZSM-5 was evaluated from the breakthrough curves of ethylene and desorption curves of ethylene transformation products measured on a zeolite bed between 308K and 523K. The kinetics of the overall immobilization/mobilization reaction was measured on a series of HZSM-5 samples in an integral flow reactor with a fixed bed of zeolite at 623K. The aluminum content of the samples ranged from 3.2 to 6.4 Al atoms per unit cell. The zeolites were characterized by XRD, SEM, chemical analysis, 27Al MAS NMR, water sorption, TPD of NH3 and FTIR spectroscopy. The results of kinetic measurements are represented by a family of S-shaped curves plotted as ethylene conversion versus contact time. The form of the curves suggests a contribution of an autocatalytic rate step to the kinetics. The length of the induction period increases with increasing crystal size and decreasing aluminum content in the catalyst. The kinetic curves obtained for crystals of the same aluminum content are strongly influenced by the crystal size. The ethylene breakthrough curves exhibit at the beginning a sharp breakthrough peak which decreases with accelerating oligomerization. The temperature threshold of zeolite bed production was estimated to lie at 418K. At this temperature C2–C5 hydrocarbons were found in the gas phase in the gas leaving the reactor. The curve plotted as the amount of immobilized species against the temperature of the zeolite bed exhibits a steep increase to a flat maximum occurring between 353K and 433K, followed by a steep decrease. Adsorption of water on samples loaded with the immobilized species provides information about the space accessible from the gas phase and indicates differences in the nature of immobilized species formed at different temperatures.

The accessibility of void space in MFI-type zeolite crystals, isolated and embedded in a polyimide (PI) matrix, was studied using optical microscopy coupled with an iodine indicator technique (IIT). IIT was used to estimate the adhesion between the PI matrix and the zeolitic phase, the accessibility of the zeolite void space for gas molecules as well as for characterizing the spatial distribution of embedded crystals in the composite. The channel system of the zeolitic phase in as-synthesized composites with the majority of crystals covered by a layer of PI is occupied by the solvent molecules used in composite synthesis. In untreated composites, the zeolitic phase is inaccessible to iodine sorption. Colouring patterns and colouring kinetics have been used to characterize the efficiency of the treatment for removing the PI covering layer from the crystal surface. The same techniques can be applied to characterize the treatment with regard to the desorption of solvents ( N- methyl-2-pyrrolidone, N,N -dimethylformamide, n-heptane) from the silicalite-1 channel system.

The extent of thermal template (tetra-propyl-ammonium: TPA+) removal from a silicalite-1 layer by heating in air was investigated. While a temperature of 330 °C was sufficient to eliminate all N-containing template species from the surface region of the layer (i.e., within a depth of ≈10 nm), their complete elimination from the bulk even at 550 °C was not achieved. This was caused by a series of reactions proceeding at high temperatures, involving the products of TPA+ thermal degradation. A substantial amount of C-containing template species remained in the sample even after a thermal treatment at 550 °C. A role the SiO2 phase of low organization present in the silicalite-1 layer plays in the retention of the products of thermal degradation has been proposed. Additionally, the stability of TPA+ irradiated by microwaves was examined. Only minor morphological changes of the layer upon thermal template removal were revealed by atomic force microscopy.

Texture characteristics of fluid catalytic cracking (FCC) catalysts were evaluated from N-2 adsorption and mercury porosimetry measurements. A hierarchy of four levels of voids were found and quantified in the beds of FCC particles. Diffusion coefficients of intraparticle diffusion for n-octane were measured in the catalyst beds by PFG NMR technique. The diffusion coefficients exhibit a linear dependence oil parameters xi that involve the mean Value of the pore radii (r) over bar in the pertinent porosity region and a function of the corresponding porosity. A strong linear correlation was also found between the parameter xi for macropores and that for mesopores. The mean sizes of macro- and mesopores thus become key parameters in tuning the FCC catalyst properties.

Pulsed-field gradient nuclear magnetic resonance (PFG NMR) has been applied to study molecular diffusion in industrial fluid catalytic cracking (FCC) catalysts and in USY zeolite for a broad range of molecular displacements and temperatures. The results of this study have been used to elucidate the relevance of molecular transport on various displacements for the rate of molecular exchange between catalyst particles and their surroundings. It turned out that this rate, which may determine the overall rate and selectivity of FCC process, is primarily related to the diffusion mode associated with displacements larger than the size of zeolite crystals located in the particles but smaller than the size of the particles. This conclusion has been confirmed by comparative studies of the catalytic performance of different FCC catalysts.

A combined flow technique for study of sorption properties of clay materials has been developed. First, water desorption is recorded and, subsequently, simultaneous measurements of water adsorption and of clay-bed expansion are performed. The technique is expected to become a powerful tool for determination of the generic type of clay materials and to provide information on the content of smectic components in the clay. From adsorption-desorption runs, data on equilibrium sorption of water in clay and on the sorption kinetics can be obtained.

Diffusivities of n-octane in particles of industrial fluid catalytic cracking (FCC) catalysts and in zeolite USY, which is the main zeolitic component of the particles, are reported. Diffusion measurements have been performed by using pulsed field gradient (PFG) NMR for a broad range of molecular displacements and temperatures. The recorded diffusivities are used to evaluate the relevance of various transport modes in the particles of FCC catalysts, such as diffusion in the micropores of the zeolite crystals located in the particles, diffusion through the surface layer of these crystals, and diffusion in the meso- and macropores of the particles, for the rate of molecular exchange between catalyst particles and the surrounding atmosphere. This rate is shown to be primarily related to the diffusion in the meso- and macropores of the particles under the condition of fast molecular exchange between these pores and the zeolite crystals located in the particles. The diffusivity associated with this type of diffusion (i.e., the intraparticle diffusivity) is found to correlate well with the catalytic performance of FCC catalysts having the same fractions of the same zeolite USY but different systems of meso- and macropores.

A technology was developed for preparation of low-cost ceramic filtration elements in the form of disks, 20 and 25 mm in diameter. The material of the elements is based on fused a-alumina as well as ceramic and glaze binders. The lateral parts are hermetized with a glaze. High reproducibility of porous structure characteristics is due to uniaxial pressing of the elements. The basic porous element with a mean pore size of 12 mum can be used, e.g., to remove solid aerosols from gas streams and thus to protect sensitive devices. Asymmetric porous elements are prepared by building a thin ceramic layer of fine alpha-alumina powder on the basic porous element. These two-layer elements can be used as supports for preparation of inorganic membranes and in other technologies.

A technology was developed for preparation of low-cost ceramic filtration elements in the form of disks, 20 and 25 mm in diameter. The material of the elements is based on fused α-alumina as well as ceramic and glaze binders. The lateral parts are hermetized with a glaze. High reproducibility of porous structure characteristics is due to uniaxial pressing of the elements. The basic porous element with a mean pore size of 12 μm can be used, e.g., to remove solid aerosols from gas streams and thus to protect sensitive devices. Asymmetric porous elements are prepared by building a thin ceramic layer of fine α-alumina powder on the basic porous element. These two-layer elements can be used as supports for preparation of inorganic membranes and in other technologies.

The removal of tetrapropylammonium cations (TPA+) from silicalite-1 crystals with a morphology of 90°-intergrowth and different crystal sizes was investigated. The effects of the nature of the gas (air or nitrogen) and of the hydrodynamics were examined using a stream flowing in parallel or across the crystal layer. The only process variable was the plateau temperature (Tmax). Crystal domain boundaries became permeable to template degradation products when Tmax exceeded 300 °C. The template removal was monitored by (i) light microscopy, (ii) degree of removal of the total organics α, of nitrogen species αN and of carbon species αC and (iii) accessibility of the channel system for N2 molecules. The sorption isotherms for N2 exhibited two steps. The upper step started to be perceptible for a degree of organic removal higher than 55%. Its height increased with α, and its position moved to lower pressure values. The plots of the gas accessibility versus the degree of removal were modelled. For template removal in air, all plots were linear. In a non-oxidizing atmosphere, the accessibility lagged behind αN. Light microscopy showed that template degradation started along domain boundaries. Sorption kinetics of iodine into silicalite-1 crystals treated in a non-oxidizing atmosphere was considerably slower than that observed into crystals calcined in air. The tendency to crack formation increased with crystal size. The template removal efficiency was higher when using cross-flow than parallel flow calcination.

conceivable limiting models of growth kinetics of polycrystalline layers involving diffusion of low molecular silicon containing species, Brownian motion of nanoparticles and their sedimentation are analyzed from the point of view of their application to the preparation of zeolite-based membranes. The activation energies derived using these models were evaluated and the effect of support orientation was quantified. A criterion of a relative importance of colloidal particle sedimentation with respect to the Brownian motion was formulated.

This chapter discusses topochemical changes in large MFl-type crystals upon thermal treatment in oxidizing and nonoxidizing atmosphere. Tetrapropylammonium hydroxide (TPAOH) removal from large as syntesized silicalite-1 crystals with internal morphology of 90°-intergrowths has been investigated in regimes with gas flow in parallel to and through the crystal layer both in the absence and presence of oxygen. The void space accessibility of crystals is estimated from the sorption isotherms of nitrogen (N2), which is exhibited as a rule two step. The topochemical changes in crystals after a partial template removal are evaluated using light microscopy, electron spectroscopy for chemical analysis (ESCA) measurements, and elemental analysis of organic residues.

Publisher Summary This chapter discusses the immobilization and mobilization of surface species during transformation of ethylene over HZSM-5 catalysts. Amount of ethylene immobilized in HZSM-5 catalysts is estimated from sorption and reaction dynamics as a function of reactor temperature. Space accessible in loaded crystals is measured using water sorption at 298 K.

The long-term sorption kinetics of p-ethyltoluene on HZSM-5 zeolite was investigated using a McBain balance. The kinetic data suggested that the transport is coupled with immobilization. In situ isomerization of p-ethyltoluene as well as temperature-programmed desorption (TPD) of the samples containing a preloaded mixture of ethyltoluenes were followed by Fourier transform infrared spectroscopy (FTIR). TPD results indicate that no significant release of immobilized m-ethyltoluene was observed at temperatures below 543K. TPD patterns of p-ethyltoluene were found to depend strongly on the temperature of the zeolite preloading. The removal and/or isomerization of p-ethyltoluene molecules trapped by the m-ethyltoluene species immobilized on the strong acid sites can occur only when the meta-isomer leaves the zeolite channels at temperatures above 543K.