Crystallization of ZSM-5 zeolite from a gel using n-butylamine as structure-directing agent was studied. Extreme high-resolution transmission and scanning electron microscopy showed the presence of dendritic features that are present at the crystal surface during most of the reaction time that become smoother towards completion of the crystallization. In addition, a web that likely stems from the gel, comprised of alumina-rich nanoparticles between the dendrites at the surface of the crystals was also identified. When the gel is not in direct contact with the crystal surface, dendrites and the web are not observed, and the crystals grow faster. Thus, the alumina-rich web retards the crystal growth and cause the formation of dendritic features.

In the present work, a carbon/cobalt composite was prepared and evaluated for adsorption of ecologically harmful tannic acid (TA). The composite was prepared by simply mixing phenolic resin with ZIF-67 and following by carbonization. TEM and SEM images showed that ZIF-67 was etched by phenolic resin and cobalt nanoparticles were formed and evenly distributed in carbon. Macroporous structure was generated between the carbonized phenolic resin and ZIF-67. N₂ adsorption-desorption isotherms results exhibited that the composite also had both micro- and meso-pores (average pore size of 5 nm) with a high surface area of 393 m² g⁻¹. Porous structure and evenly distributed cobalt nanoparticles facilitated the diffusion and adsorption of TA due to the formation of the complex between TA macromolecules and cobalt. The highest observed adsorption amount was as high as 2778 mg g⁻¹, significantly higher than that of the carbon prepared from carbonization of phenolic resin (205 mg g⁻¹) and ZIF-67 (1375 mg g⁻¹). The carbon composite material is easy to recover and reuse due to the magnetic property. The reuse experiment also showed high stability of the composite. All of the results indicated a great potential of the developed carbon composite material in wastewater treatment in the industry.

The crystallization of ZSM-5 from a gel comprising n-butylamine as structure directing agent was investigated. The samples were characterized by X-ray diffraction, nitrogen gas adsorption, extreme high-resolution transmission and scanning electron microscopy, and energy dispersive spectroscopy. The gel was found to be composed by a silica-rich matrix embedded in a skeleton of alumina-rich nanoparticles. During growth of the crystals, the silica-rich matrix is consumed first, and an increasing fraction of the alumina-rich nanoparticles are utilized later in the growth process. This leads to a non-uniform consumption of the gel walls during crystal growth. Consequently, the Si/Al ratio of the gel is steadily decreasing, which is accompanied by a corresponding decrease in the Si/Al ratio from the center to the outer surface of the crystals, i.e. Al-zoning of the ZSM-5 crystals.

Silicalite-1 films grown on gold surfaces seeded with colloidal crystals with a size of 60, 165 and 320 nm were investigated by reflection–absorption infrared spectroscopy, scanning electron microscopy and X-ray diffraction in order to follow up the formation of nano-scale defects and to determine the optimal synthesis conditions for preparation of silicalite-1 films with a low concentration of defects. Using 60-nm-sized colloidal crystals, the seeding method was capable of producing silicalite-1 films with low concentrations of defects and with thicknesses ranging from 100 to 300 nm, which are predominantly oriented with the a-axis perpendicular to the surface. Hydrothermal treatment times of the 60-nm-seeded surfaces longer than 36 h as well as the seeding with 165 or 320 nm colloidal crystals substantially enhanced the formation of defects in the films.

1H NMR pulsed field gradient was used to study self-diffusion of a phosphonium bis(salicylato)borate ionic liquid ([P6,6,6,14][BScB]) in the pores of Vycor porous glass at 296 K. Confinement in pores increases diffusion coefficients of the ions by a factor of 35. However, some [P6,6,6,14][BScB] ions demonstrated apparent diffusion coefficients much lower than their mean values, which may be due to partially restricted diffusion of the ions. We suggest that this fraction corresponds to areas where ions are confined by pore ‘necks’ (micropores) and empty voids. Heating of the ionic liquid / Vycor system at 330 K led to a change in the diffusivity of the ions, because of their redistribution in the pores. The size of the bounded regions is on the order of 1 µm, as estimated from the dependence of the ion diffusivity on the diffusion time.

Zeolite ZSM-5 (SiO2/Al2O3 ratio 53:1) ion exchanged with Cu2+ to 0%, 74% and 160% was characterized by X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Infrared (IR) spectroscopy, Electron spectroscopy for chemical analysis (ESCA) and ammonia desorption. A more limited set of data was obtained for Cu-ZSM-5-33, ion exchanged with 0%, 104% and 210% Cu2+ ions. All catalysts lose water below 100°C. More strongly bound water, approximately two molecules per Cu2+ ion, emerge at a higher temperature. This corresponds either to an incomplete hydration shell for zeolite-bound Cu2+ ions or to the decomposition of Cu(OH)2 and simultaneous reactive adsorption of copper ions on the inner surface of the zeolite. The process occurs in the same temperature range, 150-350°C, where XRD reveals rearrangements in the H-form of the catalyst. Reactions between the exchangeable cations and the zeolite appear critical for lattice changes and possibly the formation and dispersion of catalytically active centers at these temperatures. Dehydroxylation and water desorption are observed between 350°C and 450°C for H-ZSM-5. This temperature range overlaps with the light-off temperature for direct NO decomposition over Cu-ZSM-5. This coincidence can be rationalized in terms of two effects of enhanced ionic mobility and dynamics of the zeolitic framework. ESCA shows that partial reduction, cupric to cuprous, occurs as a result of annealing in the same temperature range. It has been suggested that NO-derived surface intermediates act as site blockers for the direct decomposition below the light-off temperature until destabilized by lattice movements. The lower stability and thus higher mobility of low SiO2/Al2O3 ratio ZSM-5 zeolites would then rationalize an advantage of these materials as supports in catalysts for direct NO decomposition.

Bolivian diatomite was successfully used as a silica source for the synthesis of zeolite Y. Prior to synthesis, the diatomite was leached with sulfuric acid to remove impurities and aluminum sulfate was used as an aluminum source. The raw materials were reacted hydrothermally at 100 °C in water with sodium hydroxide and different Na2O/SiO2 ratios were investigated. The final products were characterized by scanning electron microscopy, X-ray diffraction, gas adsorption and inductively coupled plasma-atomic emission spectroscopy. Diatomites originating from different locations and therefore containing different types and amounts of minerals and clays as impurities were investigated. After optimization of synthesis time, zeolite Y with low SiO2/Al2O3 ratio (3.0–3.9) was obtained at a high yield for high alkalinity conditions (Na2O/SiO2 = 0.85–2.0). Lower Na2O/SiO2 ratios resulted in incomplete dissolution of diatomite and lower yield. Nevertheless, decreasing alkalinity resulted in a steady increase of the SiO2/Al2O3 ratio in zeolite Y. Consequently, it was possible to synthesize almost pure zeolite Y with a SiO2/Al2O3 ratio of 5.3 for a Na2O/SiO2 ratio of 0.6, albeit at a low yield. In this respect, diatomite enables the synthesis of high silica zeolite Y and behaves similarly to colloidal silica in traditional syntheses, with both sources of silica having in common a high degree of polymerization. Interestingly, the presence of minerals and clays in the starting diatomite had marginal effects on the outcome of the synthesis. However, their dissolution resulted in presence of calcium and magnesium in the zeolite Y crystals. Finally, overrun of all investigated compositions resulted in the formation of zeolite P nucleating and growing onto dissolving zeolite Y crystals, which was shown to be triggered when aluminum was completely depleted at high alkalinity

Monolithic binder-free CO₂ adsorbents with high adsorption capacity, selectivity, adsorption-desorption kinetics, and regenerability are highly desired to both reduce the environmental impact of anthropogenic CO₂ emissions and purify valuable gases from CO₂. Herein, we report a strategy to prepare monolithic carbonaceous CO₂ adsorbents from low-cost and underutilized bioresources, which enabled the formation of a delicate anisotropic, hierarchical porous structure. With optimized material composition and processing conditions, the biobased carbon adsorbent demonstrated a CO₂ adsorption capacity of 4.49 mmol g^-1 at 298 K and 100 kPa, relatively weak adsorbent-adsorbate affinity, good CO₂/N₂ selectivity, and advantageous hydrophobicity against water vapor. Moreover, the unique anisotropic porous structure provided high stiffness and good flexibility to the adsorbent in the axial and radial directions, respectively. We confirmed that this type of carbon adsorbent could be packed in a column for dynamic CO₂ capture independent of any binders, indicating its promising future for further development toward widespread utilization.

In the present work, a biosynthesis route for the preparation of hierarchical pompon-like SAPO-34 was developed. Commercially available bacterial cellulose aerogel was used as template. SiO2 loaded bacterial cellulose aerogel was used as silica source and a simple hydrothermal treatment was used for crystallization. XRD, FT-IR, SEM, TEM, N2 adsorption-desorption and TG techniques were employed to characterize the obtained samples. The hierarchical pompon-like SAPO-34 showed a spherical morphology that was comprised of nanosheets with a thickness less than 30 nm. The specific surface area of the hierarchical pompon-like SAPO-34 was 498 m2/g that was higher than the trigonal SAPO-34 crystals of 465 m2/g. The ultrasonic treatment experiment indicated a high stability of the pompon-like structure. In addition, the hierarchical pompon-like SAPO-34 exhibited a CO2 adsorption capacity of 2.26 mmol/g at 100 kPa and 298K and the corresponding CO2/CH4 ideal separation factor was 5.7, which was higher than that of trigonal SAPO-34 crystals. The saturated adsorption capacity and b-value were estimated using single site Langmuir, Toth and Sips adsorption isotherm models and the observed results were constant. Compared with trigonal SAPO-34, hierarchical pompon-like SAPO-34 displayed a higher saturated adsorption capacity, but a lower b-value.

A novel sensitive chemical sensor probe has been fabricated. The sensor principle is based on silicalite-1 coated ATR (attenuated total reflection) elements and FTIR spectroscopy. The microporous silicalite-1 film enriches the analyte to the probe surface, thus increasing the sensitivity. At a relative pressure of n-hexane in helium of 6 × 10−5 the sensitivity of the probe is approximately 85 times higher for the silicalite-1 coated element compared to a 10 cm transmission gas cell and ca. 180 times higher compared to an uncoated element. The performance of the probe is illustrated by determination of an adsorption isotherm for n-hexane in silicalite-1.

Single crystal silicon (100) wafers were seeded with colloidal silicalite-1 crystals and hydrothermally treated in a precursor solution to grow thin silicalite-1 films. A total of 28 experiments in eight series were investigated with SEM and XRD to evaluate the preferred orientation of the crystals constituting the films. The investigated parameters in the film formation process were seed crystal size, amount of adsorbed seed crystals and film thickness after hydrothermal treatment of the seeded substrates. In thin films, most of the crystalline material is oriented with the b-axis perpendicular to the substrate surface. In thick films, most of the crystalline material is oriented with the a-axis perpendicular to the substrate surface. The change in preferred orientation with film thickness is faster when small seeds are used. The amount of adsorbed seeds has a larger influence on the preferred orientation when large seeds are used. A mechanism explaining these trends is proposed. The choice of size and coverage of seeds can be used to control the preferred orientation of the crystals in a film of given thickness within certain limitations.

The synthesis and evaluation of high performance MFI-type membranes is described. These systems exhibit fluxes that are one to two orders of magnitude higher than previous literature reports, with comparable selectivities, when tested for various single component gases and for mixtures of C4, C6 and xylene isomers.

These materials are the result of a rational fabrication approach targeting ultra-thin, defect-free MFI films on open supports by using a two-step support masking technique and a monolayer of colloidal nucleation seeds, followed by in situ hydrothermal growth, producing a defect-free film with a thickness of 0.5 μm. Reproducibility of the membrane preparation was excellent.

Silicalite-1 films with a thickness of 500 nm on asymmetric α-alumina micro filtration filters were calcined at 500 °C with heating and cooling rates varying between 0.2 °C/min and 5.0 °C/min. The membranes were characterized with single gas permeation, porosimetry, and xylene isomer separation experiments. It was found that the quality of the prepared membranes was independent of the heating/cooling rate according to the single gas permeation and porosimetry characterization. Xylene isomer separation data was found to vary between the samples, but none of the variations could be attributed to the heating/cooling rate during calcination since the variations did not follow a trend but occurred randomly. It is thus concluded that the calcination rate does not influence the quality of these membranes.

This work shows that a previously developed model for single gas permeation in real MFI membranes is applicable to an arbitrary MFI membrane with a different film thickness and defect distribution. The model can predict the flow of H₂, N₂ and He resonably. Deviations in SF₆ flux for thick and oriented films were observed and attributed to a lower diffusion coefficient for the narrower pores in the a-direction of the MFI crystals. By guidance from the model, variations in previously reported single gas permeance ratios for selected membranes can now be attributed to variations in feed pressure, film thickness preferred orientation and defect distribution. It was found that high feed pressures and thick oriented films resulted in large single gas permeance ratios with SF₆ in the denominator, even though these membranes were more defective than thinner membranes with more randomly oriented crystals. In general, single gas permeance ratios are strongly dependent on material properties and experimental conditions. These ratios can only be used for comparison of membranes with similar morphology and the ratios must be measured under identical conditions.

A previously developed mathematical model with parameters fitted to experimental data was used to study effects of material properties and experimental conditions on single gas permeance ratios of MFI membranes. The model showed that single gas permeance ratios are highly dependent on substrate morphology, feed pressure, crystallographic orientation and defects in the film. It was found that the pore size and the thickness of the substrate affected permeance ratios, due to mass transfer resistance in the substrate. The applied feed pressure also had a significant effect on the permeance ratios. This is due to differences in mass transfer resistance of the substrate and adsorption characteristics with varying feed pressures. The crystallographic orientation of the zeolite film also affected permeance ratios due to changes in diffusivity with varying orientation of the crystals in the film. Finally, the effect of defects was investigated. As expected, it was found that the permeance ratios decreased when more defects were added in the model. However, if the membrane is not very defective, the permeance ratio is much more affected by the substrate and by variation in pressure drop than by defects. The results in the present work show that single gas permeance ratios cannot be used directly as a benchmark of membrane quality unless all other parameters are kept constant.

Size-controllable monodispersed carbon@silica core-shell microspheres and hollow silica microspheres were prepared in a simple homemade T-type mixer by polymerization of furfuryl alcohol (FA) and hydrolysis of TEOS in H₂SO₄ water phase microdroplets to obtain polyfurfuryl alcohol (PFA)@silica microspheres, followed by carbonization and calcination. The FA and TEOS diffuse into the water phase from an oil phase. The flow rates of oil and water phase were 4 and 2 ml h⁻¹, respectively. It was found that the concentration of FA has a more significant effect on the diameter of carbon@silica core-shell microspheres than TEOS due to the template effect of the PFA core. However, the diameter of the hollow silica microspheres was influenced by the concentration of TEOS more significantly. The obtained core-shell microspheres and hollow silica microspheres have large surface area of 555 and 769 m² g⁻¹, respectively. The hollow silica microspheres have both microporous and mesoporous structure, and the percentage of mesoporous volume was as high as 89%. In addition, based on the study results, a rational formation process of the carbon@silica core-shell microsphere and hollow silica microspheres was assumed.

Rare-earth elements (REEs) are indispensable in various applications ranging from catalysis to batteries and they are commonly found from phosphate minerals. Xenon is an excellent exogenous NMR probe for materials because it is inert and its ¹²⁹Xe chemical shift is very sensitive to its local physical or chemical environment. Here, we exploit, for the first time, ¹²⁹Xe NMR for the characterization of porous structures and adsorption properties of REE phosphates (REEPO4). We study four different REEPO4 samples (REE = La, Lu, Sm and Yb), including both light (La and Sm) and heavy (Lu and Yb) as well as diamagnetic (La and Lu) and paramagnetic (Sm and Yb) REEs. ¹²⁹Xe resonances are very sensitive to the porous structures and moisture content of the REEPO4 samples. In the samples treated at a lower temperature (80 °C), free water hinders the access of hydrophobic xenon into small mesopores, but the treatment at a higher temperature (200 °C) removes the free water and allows xenon to explore the mesopores. Based on a standard two-site exchange model analysis of the variable-temperature 129Xe chemical shifts, as well as its proposed, novel modification for paramagnetic materials, the average mesopore sizes were determined. The size was the largest (79 nm) for the La sample with mixed monazite (70%) and rhabdophane (30%) phases and the smallest (6 nm) for the Yb sample with pure xenotime phase. The mesopore sizes of the Lu and Yb samples (12 and 6 nm) differed by a factor of two regardless of their similar xenotime phase. The ¹²⁹Xe NMR analysis revealed that the heats of adsorption of the samples are similar, varying between 8.7 and 10.1 kJ/mol. For diamagnetic samples, computational modelling confirmed the order of magnitude of the chemical shifts of Xe adsorbed on surfaces and therefore the validity of the two-site exchange model analysis. Overall, ¹²⁹Xe NMR provides exceptionally versatile information about the pore structures and adsorption properties of REEPO4 materials, which may be very useful for developing the extraction processes and applications of REEs.

In the present work, two ultra-thin MFI membranes, prepared using hydroxide and fluoride ions as mineralizing agents, respectively, were carefully examined by permporometry. The amount of micropore defects, as determined by permporometry, differed significantly between the two different membranes. For the first time, it was demonstrated that the micropore defects determined by permporometry were most likely open grain boundaries. The results were verified by direct observation of the open grain boundaries by a state-of-the-art XHR-scanning electron microscopy instrument. In addition, the permporometry data were also consistent with permeation data using 1,3,5-trimethylbenzene (TMB) as a probe molecule, separation data using an equimolar mixture of n-hexane and TMB, and nitrogen adsorption data.

In the present work, two ultra-thin MFI membranes, prepared using hydroxide and fluoride ions as mineralizing agents, respectively, were carefully examined by permporometry. The amount of micropore defects, as determined by permporometry, differed significantly between the two different membranes. For the first time, it was demonstrated that the micropore defects determined by permporometry were most likely open grain boundaries. The results were verified by direct observation of the open grain boundaries by a state-of-the-art XHR-scanning electron microscopy instrument. In addition, the permporometry data were also consistent with permeation data using 1,3,5-trimethylbenzene (TMB) as a probe molecule, separation data using an equimolar mixture of n-hexane and TMB, and nitrogen adsorption data

The effect of heating rate on thermal behavior of TPA-silicalite-1 during calcination and the reaction kinetics for TPA decomposition were investigated. The cell parameters of the TPA-silicalite-1 during the heating cycles were determined with the aid of high temperature X-ray diffraction data and the Rietveld method. The template decomposition is accompanied by a large contraction of the unit cell. The unit cell dimensions during template removal are not affected significantly by the heating rate. Consequently, the rate of contraction is approximately proportional to the heating rate. The intensity of some diffraction peaks changes during heating, especially the 101/011 and the 200/020 peaks. The intensity change of those peaks shows the same dependence with temperature as the TPA occupancy, indicating that these parameters are related. An analysis of the kinetics for TPA decomposition based on the intensity change of the 101/011 and the 200/020 peaks was performed. The apparent activation energy (Ea) of the template decomposition in silicalite-1 determined with the Kissinger and the Flynn–Wall–Ozawa methods was 138 (±25) and 138 (±29) kJ mol−1, respectively. The reaction order, determined with the method of Kennedy and Clark, was close to 0.5 indicating that the rate-limiting step is mono-dimensional diffusion. Ea was 140 (±30) kJ mol−1, in good agreement with the results obtained with the other methods.

With the results presented here, it is possible to discuss possible effects of the heating rate on the crack formation frequently observed in zeolite membranes during calcination.

Thin and continuous Faujasite-type films were synthesized on α-alumina wafers using a seeding technique. Surface modified wafers were seeded with colloidal zeolite Y crystals prior to film growth in a synthesis mixture. The effects of hydrothermal treatment on film thickness, morphology and preferred orientation of the crystals constituting the film were investigated using scanning electron microscopy and X-ray diffraction. During hydrothermal treatment a precipitate formed rapidly, leaving an almost clear solution in the upper part of the reactor. Experiments at 60–100°C were performed with the sample placed in the upper part of the synthesis solution. An increase in the film growth rate with increasing temperature was observed. Adsorbed seeds were shown to be oriented with the {1 1 1} pyramid, parallel to the substrate surface. A change in the orientation with film growth was noted, probably due to the attachment of secondary crystals to the growing film surface. In one experimental series, film growth was effected at the bottom of the tube at 100°C. Faster film growth and multilayered films were obtained. A decrease in the film thickness after prolonged hydrothermal treatment was observed in all experimental series. This is probably due to the dissolution of the film and formation of zeolite P in the synthesis solution. The thicknesses of the films synthesized in this work are in the range of 150–2700 nm. The films are promising candidates for use in membrane applications.

Carbon microspheres with a uniform size of about 170 μm were prepared in a simple co-flow microfluidic device using solvent extraction method. An ethanol solution of colloidal silica and phenol formaldehyde (PF) resol was used as the dispersion phase, and a mixture of hexane and diisopropylamine was used as the continuous phase. The droplets of PF resol resin/silica were generated in the continuous phase. Colloidal silica assisted the formation of the spherical structure and worked as a pore generator. The continuous phase was also used as extractant and catalyst for PF resin/silica microspheres formation. Curing, drying, carbonization and leaching were used for the post-treatment of the PF resin/silica microspheres to obtain porous carbon microspheres. The carbon microspheres displayed a narrow size distribution and a high surface area of 679 m²/g coupled with adjustable mesopores and large mesopore volume. Carbon microspheres prepared from the dispersion phase with different PF/silica ratios (denoted as carbon/silica (C/Si) ratios) were studied and the formation mechanism of the PF/silica microspheres was deeply explored.

In the present work, C@TiO₂ core-shell adsorbents were successfully prepared and the adsorption capacities for rhodamine B (RB) were investigated at different conditions. The adsorbents were prepared by first in-situ hydrolysis and deposition of TBOT on the surface of ZIF-8 nanoparticles to obtain ZIF-8@titania gel, and then carbonization. XRD, SEM, TEM, and N₂ adsorption-desorption techniques were employed to characterize the adsorbents. The results showed that the adsorbents were comprised of TiO₂ shell and carbon core. Large surface area and hierarchical pores, which were different from ZIF-8 derived porous carbon, were generated due to the less contraction of carbon during carbonization when robust TiO₂ shell covered on the surface. The highest adsorption capacity for RB was 298 mg/g on C@TiO₂. Apart from the hierarchical pores and large surface area, the low surface charge of C@TiO₂ core-shell adsorbents was also observed, which also contributed to the high adsorption capacity for cationic dyes. The reuse experiments showed that the adsorbents maintained the high adsorption capacity after 5 cycles. The high stability is crucial for practical application.

In the present work, novel porous C@C composite adsorbents were prepared and applied for the adsorption of methylene blue (MB) and rhodamine B (RB). The adsorbents were prepared by carbonizing resorcinol–formaldehyde (RF) resins-coated ZIF-8 composites that obtained using an in-situ deposition method. The effect of RF/ZIF-8 ratio and carbonization temperature on the particle size, specific surface area and pore size was investigated. High adsorption capacity resulted from the high surface area of 1842 m²/g and a sufficient pore size of 4.4 nm. The effect of temperature, initial dyes concentration and pH on the adsorption capacity was investigated to optimize the adsorption conditions, and maximum adsorption capacity of 681 and 462 mg/g was observed for MB and RB, respectively. Langmuir model and pseudo-second-order adsorption kinetics model can be used to well describe the obtained adsorption isotherms. The estimated saturated adsorption capacity for MB and RB was 806 and 476 mg/g, respectively. The used C@C-1000 could be regenerated in methanol solution, and after 5 cycles, the adsorption capacity was maintained above 92% of the maximum.

A two-stage-varying-temperature synthesis procedure, which involves a rapid change in temperature at some point during the course of crystallization, was applied to the synthesis of discrete colloidal particles of TPA-silicalite-1. As the duration of the period at the initial synthesis temperature was extended, the crystal concentration and ultimate crystal size varied until they were approximately equal to those obtained for a complete synthesis at the initial temperature. At this point in the crystallization, it was concluded that the nucleation stage was completed. For syntheses performed at 60, 80 and 100°C, the duration of the nucleation period determined by this method was about 100 h, between 4 and 6 h and less than 2 h, respectively. Thus, nucleation, for this system, is a continuous process, and it was found that the rate of nucleation, which is initially high, declines, throughout the nucleation period. In all cases, nucleation occurred during an induction period when little or no crystal growth was observed, which explains why the syntheses yielded a product with a rather narrow crystal size distribution. If, for the two-stage syntheses, the temperature change was made after completion of the nucleation period, the second synthesis temperature controlled only the linear growth rate of the crystals and the final yield of silicalite-1 obtained

Supported zoned and sandwiched MFI films were prepared by a two-step crystallization procedure, using seeds. In this work, a zoned MFI film is defined as one assembled by crystals propagating from the support to the film top surface with varying Al content along the length of the crystal. A sandwiched MFI film is referred to as one assembled by at least two layers of crystals. Six types of films were prepared, both zoned and sandwiched, with a high or a low Al-content in the ZSM-5 part and with varying order of the layers, i.e. ZSM-5 coated with silicalite-1 or vice versa. The films were characterized by SEM and TEM. The Al-distribution was measured by cross-sectional EDS, and the preferred orientation of the crystals could be determined by XRD. Truly zoned films are obtained when the compositional difference between the layers is relatively small, and the synthesis conditions are similar or when the first layer is silicalite-1. If the first layer is ZSM-5 and the synthesis conditions and/or the composition vary too much, a discontinuity occurs at the interface between the layers, and sandwiched film results, where nucleation of the second layer is initiated by secondary nucleation or by applying seeds.

The effect of varying silica source on the nucleation and crystallization of TPA-silicalite-1 was investigated. A direct experimental method, involving a two-stage varying-temperature synthesis, was used to determine the nucleation period for colloidal crystals of TPA-silicalite-1 with different silica sources, including tetraethoxysilane (TEOS) and amorphous silica (Ludox TM and Ludox LS). For syntheses performed at 60°C with TEOS as silica source, the duration of the nucleation was about 72 h, and a very rapid increase in the crystal population occurred during the initial crystallization time. However, with the amorphous silica sources (Ludox TM or Ludox LS), the duration of the nucleation period was extended to about 120 h, and the nucleation profile consisted of a self-accelerating nucleation rate at the beginning of the nucleation period. The two-stage synthesis method could be used to determine the nucleation profile for the various silica sources. However, this technique overestimated the crystal concentration at the earliest stage of nucleation with amorphous silica. The use of amorphous silica gave rise to a broader crystal size distribution compared to that of TEOS. However, it was found that for both TEOS and amorphous silica the vast majority of the nucleation occurred during an induction period when little or no crystal growth was observed. In addition, Raman spectroscopy revealed structural differences between Ludox TM and Ludox LS which may account for differences in the nucleation processes observed for these two amorphous silicas.

Colloidal zoned MFI crystals, i.e., continuous crystals with a compositional gradient resulting in a ZSM-5 core covered with a silicalite-1 shell, were synthesized by the addition of ZSM-5 seeds to a silicalite-1 synthesis solution. The effect of the surface aluminum content of the ZSM-5 crystals on the synthesis of the zoned MFI crystals was investigated using SEM, TEM, XPS and XRD. An acid treatment of the ZSM-5 seeds, which removed some of the aluminum at the surface, proved favorable for the synthesis of zoned MFI crystals.

The structure of silicalite-1 films grown on seeded gold surfaces is investigated by modelling the observed changes in the infrared reflection absorption (IRRA) spectra of samples treated for different times in the synthesis solution. The results show that a gradual deformation of the five-membered silicon-oxygen rings occurs during the first 11 h of the hydrothermal treatment which leads to breaking of Si---O---Si linkages and to formation of linear defects along the c-axis. Interactions between the dislocations and the grain boundaries during the further growth of the film provoke the appearance of void spaces in the grain boundary interface which may cause incipient cracking in the silicalite-1 films on seeded gold surfaces. The range 1000-1300 cm-1 in the IRRA spectra is found to be appropriate for estimating the quality of silicalite-1 films grown on metal surfaces.

Novel structured adsorbents in the form of thin zeolite films grown on substrates designed for low pressure drop have a great potential to improve pressure swing adsorption (PSA) processes. In the present work, template free films of NaX zeolite were grown on the walls of ceramic cordierite supports using a seeding technique. The supports had 400 parallel channels per square inch. Films were grown both from a gel and a clear synthesis solution. The materials were analyzed by scanning electron microscopy, X-ray diffraction, N2 adsorption/desorption measurements, Hg-porosimetry as well as CO2 breakthrough experiments. When a gel was used for film growth, a film consisting of well intergrown crystals with a thickness of about 1 μm was obtained. However, a large amount of sediments were deposited on top of the film, which resulted in a dispersed CO2 adsorption breakthrough front. Zeolite films grown in one longer hydrothermal treatment in a clear solution were less intergrown and consisted of both NaX and hydroxysodalite crystals and, in addition, some sediments were deposited on top of the film, which again resulted in a dispersed breakthrough front. By using a multiple-step synthesis procedure and a clear synthesis solution, well intergrown NaX films, free from sediments and with only a very small fraction of hydroxysodalite crystals could be prepared. The CO2 breakthrough front for the latter adsorbent was sharper than the front for an empty adsorption column and only shifted in time. This indicates that the flow distribution in the adsorbent is even and that the mass transfer resistance in the film is very low due to the small film thickness and high effective diffusivity for CO2 in the NaX film and still, the adsorption capacity is considerable. The even flow distribution, very low mass transfer resistance and low pressure drop in combination with considerable adsorption capacity in this adsorbent indicates that it is a promising adsorbent for PSA applications. The findings from the present work will be important for the development of structured adsorbents to use as a competitive alternative to traditionally used adsorbents in PSA.

MFI crystals or films with controlled thicknesses and different Si/Al ratios were grown on seeded cordierite monoliths using a clear synthesis mixture with template or a template-free gel. The materials were analyzed by scanning electron microscopy, X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, X-ray photoelectron spectroscopy, thermogravimetric analysis and sorption experiments using N2 or NO2 adsorbates. The films were uniformly distributed over the support surface. As expected, the specific monolayer N2 adsorption capacity (mol/gzeolite) was constant and independent of film thickness. The specific molar NO2 adsorption capacity was significantly lower than the specific molar monolayer N2 adsorption capacity, indicating that NO2 is adsorbed at specific sites rather than evenly distributed in a monolayer. A number of NO2 adsorption sites with varying strengths were observed by TPD experiments. At 30 °C, the amount of adsorbed NO2 in the MFI films increased with increasing Al and Na content as opposed to the N2 adsorption capacity, which was independent of these parameters. At 200 °C, the adsorbed amount of NO2 was lower than at 30 °C and apparently independent on Al concentration in the Na-MFI films. These results indicate that different mechanisms are involved in NO2 adsorption. NO2 may adsorb weakly on Na+ cations and also react with silanol groups and residual water in the zeolite, the latter two results in more strongly bound species. Upon NO2 adsorption, formation of NO was observed. This work represents the first systematic study of the effects of Al and Na content on NO2 adsorption in MFI films.

ZSM-5 zeolite crystals with carefully controlled thicknesses in the range 20–110 nm, i.e. in the colloidal domain, were synthesized in fluoride and hydroxide media. The crystals were treated in steam at high temperature to evaluate the stability and evaluated by SEM, XRD, NMR and NH3-TPD. The results showed that the framework of crystals synthesized in fluoride media was more stable than the framework of crystals synthesized in hydroxide media. This should be an effect of lower concentration of structural defects and silanol groups in the former zeolites as reported by other groups. However, independently of the synthesis conditions, all crystals dealuminated rapidly when treated with steam at the conditions investigated in the present work.

A multi-step procedure for the preparation of meso/macroporous AlPO-5 spherical macrostructures using cation exchange resin beads as macrotemplates is presented. Firstly, aluminum species were introduced into the resin beads by ion exchange resulting in a resin-aluminum composite. Thereafter, the resin-aluminum composite was mixed with TEAOH, H3PO4 and distilled water and hydrothermally treated at 150 °C to yield resin-AlPO-5 composite. Finally, the resin was removed by calcination leaving behind self-bonded AlPO-5 spheres. The product AlPO-5 macrostructures were thoroughly characterized by SEM, XRD, nitrogen adsorption measurements, 31P and 27Al solid state NMR spectroscopy. The influence of various components of the synthesis mixture on the crystallinity, phase purity and stability of the AlPO-5 spheres was systematically studied. Samples prepared for different treatment times using the initial synthesis composition that gives spheres of the highest quality were used to study the crystallization process within the resin.

Silica-based spherical macrostructures containing vanadium and tungsten oxides were prepared using anion exchange resin beads as a shape-directing macrotemplate in a multi-step procedure. In a first step resin beads were treated with a clear and homogeneous TPA-silicate synthesis solution at 170 °C for three different times and resin-silicate composites were obtained. Short treatment times resulted in amorphous silica whereas the longest time yielded highly crystalline silicalite-1. In a second step anionic vanadium or tungsten species were introduced into the resin-silicate composites by utilization of the residual ion exchange capacity of the resin. In a final step the ion exchange resin was removed by calcination leaving behind vanadium- or tungsten-containing silica spheres. The influence of the concentration and the pH of the solutions used for vanadium and tungsten ion exchange on the properties of the final spheres was investigated. The product particles were extensively characterized by XRD, SEM, AAS, nitrogen adsorption measurements, Raman and UV–vis diffuse reflectance spectroscopy. Generally, the nature of the metal species formed within the spheres was isolated and highly dispersed monomers in tetrahedral coordination in amorphous samples and V2O5 or WO3 crystallites in crystalline ones.

Vanadium modified AlPO-5 spheres were prepared using a cation exchange resin as a macrotemplate. Initially, a AlPO-5–resin composite was obtained by a hydrothermal treatment of preformed Al–resin composites with a mixture of phosphoric acid, tetraethyl ammonium hydroxide and distilled water. Vanadium was introduced in a subsequent step into the AlPO-5–resin composite by a secondary ion exchange reaction. The final self-bonded vanadium modified AlPO-5 spheres were obtained by combustion of the organic ion exchanger. Product particles were characterized by SEM, XRD, AAS, nitrogen adsorption measurements, Raman and UV–vis diffusion reflectance spectroscopy. Materials with controlled macroshape and porosity were prepared by the approach. Further, control of amounts of vanadium present within the AlPO-5 spheres was achieved by varying the concentration of the vanadium solution used for ion exchange. The nature of the vanadium species present was dependent on the metal loading. Isolated and highly dispersed vanadium in tetrahedral coordination was present at low loadings, whereas polymeric and/or V2O5 crystallites were observed at higher loadings.

The adsorption and mass transport of CO₂ and CH₄ in CHA zeolite were studied experimentally. First, large and well-defined CHA crystals with varying Si/Al ratios and morphologies ideal for adsorption studies were prepared. Then, adsorption isotherms were measured, and adsorption parameters were estimated from the data. In the next step, permeation experiments for pure components and mixtures were conducted for a defect-free CHA membrane with a Si/Al ratio of 80 and a thickness of 600 nm over a wide temperature range. A maximum selectivity of 243 in combination with a CO₂ permeance of 70 × 10⁻⁷ mol/(m² s Pa) was observed for a feed of an equimolar CO₂/CH₄ mixture at 273 K and 5.5 bar. Finally, a simple model accounting for adsorption and diffusion through the surface barriers and the interior of the pores of the membrane was fitted to the permeation data. The fitted model indicated that the surface barrier was a surface diffusion process at the pore mouth with higher activation energy than the diffusion process within the pores. The model also showed that the highly selective mass transport in the membrane was mostly a result of a selective surface barrier and, to a lesser extent, a result of adsorption selectivity.

A direct experimental method, involving a two-stage varying-temperature synthesis, was utilized to investigate the effects of aging on the nucleation kinetics for the synthesis of nanosized TPA-silicalite-1 with various silica sources, including tetraethoxysilane (TEOS) and amorphous silica Ludox TM. For TEOS aging had only a mild influence on the nucleation and crystallization kinetics, whereas for Ludox TM dramatic changes occurred. After extended aging periods, the nucleation kinetics for syntheses with Ludox TM became similar to those for syntheses with TEOS, leading to increasing similarities in the properties of the products of the crystallization. Independent of aging time and silica source, the nucleation processes occurred over a substantial period of time, extending over the induction period, but were completed before crystal growth was detected. With increased aging, the nucleation period was gradually decreased and tended to be completed earlier in the induction period. Raman spectra revealed that with Ludox TM, aging enhanced the interaction between TPA+ and the silica species, leading to an increase in the concentration of precursor species for nucleation, which in turn accelerated the nucleation rate.

MFI films with a thickness of about 550 nm were prepared on α-alumina substrates. The surface Si/Al ratios (XPS) were 157 and 62 for silicalite-1 and ZSM-5 films, respectively, and in accordance, XRD data indicated lower ratios for ZSM-5 films. Higher ratios were observed by ICP-AES for crystals grown in the bulk of the synthesis mixtures. Six membranes of each type were prepared. Porosimetry measurements showed that all membranes were of high and similar quality. Single gas permeances for H2, N2, He, CO2 and SF6 at 25 °C were very similar within each type of membranes. However, the average hydrogen permeance was 27% lower and the average H2/SF6 single gas permeance ratio was 67% higher for ZSM-5 membranes. These differences are attributed to a narrower effective pore diameter for the ZSM-5 membranes due to the sodium counter ions. Separation of mixtures of H2O, H2 and n-hexane (helium balance) was investigated in the temperature range 25-350 °C. The highest separation factors α-H2O/H2 were observed at 25 °C and were 14.3 and 19.7 for silicalite-1 and ZSM-5, respectively. The membranes were selective also at 100 °C and the separation factors were about 3.2 and 6 for silicalite-1 and ZSM-5, respectively. However, the selectivity decreased at elevated temperatures and the separation factor approached 1 at temperatures above 180 °C for both membrane types. The observed water selectivity was attributed to weak adsorption of water on polar sites. A low (1.5-3) α-H2O/n-C6 separation factor was observed for both membrane types for the entire investigated temperature range.

In this study, an efficient procedure for controllable synthesis of uniform mesoporous ZSM-5 single crystals with various crystal architectures and high mesoporosity was developed. Compared with conventional ZSM-5 catalyst, mesoporous ZSM-5 single crystals synthesized by this method exhibited significantly higher external surface area and larger mesopore volume than conventional one. The catalytic performance of mesoporous zeolites were evaluated in the conversion of methanol to hydrocarbons using a fixed-bed reactor operating at 370 °C, atmospheric pressure and weight hourly space velocities (WHSV) of 0.16 to 6.58 h−1. By controlling the ZSM-5 synthesis procedure, the activity and stability of the ZSM-5 catalyst in the conversion of methanol to gasoline-range hydrocarbons can be favorably tuned. We also found that mesoporosity plays a crucial role in catalyst stability. Good correlation was observed between catalyst lifetime and mesoporosity. While the catalyst activity is related to the acid site density, the catalyst stability (deactivation rate) correlates with the measured surface ratio of BET and external surface area (SBET/SMeso). The novel ZSM-5 catalyst exhibited improved stability due to the faster removal of products with shorter diffusion path-length and lower coke formation. The obtained results indicated that the novel mesoporous ZSM-5 catalyst containing relatively large pores (mostly mesopores) enhances reaction yield towards gasoline-range hydrocarbons. It is therefore concluded that the relatively slow deactivation rate (coke formation) of novel mesoporous ZSM-5 single crystals catalyst makes this zeolite the preferred catalyst for the conversion of methanol to gasoline-range hydrocarbons at mild conditions.

Calculations have been performed to investigate the possibility for hydrogen adsorption in the manganese containing metal-organic framework MOF-73. A supercell of 348 atoms in total were employed and the computer code Aimpro with the LDA functional PW92 was used to relax the different structures in the study. The results clearly show that MOF-73 is a suitable candidate for hydrogen storage since the coordination/binding energy for a hydrogen molecule to the MOF structure falls in the range of a few tens of kJmol-1.

The question as to whether silicalite-1 grows via an aggregation of smaller particles or similar sized particles has been addressed by considering the fundamentals governing colloidal stability - the quantitative theory underlying colloidal stability being given by the extended Derjaguin-Landau and Verwey-Overbeek (DLVO) theory. Application of the extended DLVO theory to discrete colloidal particles in silicalite-1 precursor sols shows that a net repulsive interactive energy exists between the negatively charged particles. The thermal energy of the colloidal particles (1/2kT at 373 K, the crystallization temperature) is not sufficient to overcome the net repulsive energy barrier. The extended DLVO theory has been applied to two growth scenarios with similar results: growth by aggregation of particles of very different sizes and growth by aggregation of similar sized particles. The significance of these conclusions is that a proposed growth mechanism of MFI type zeolite (growth by aggregation of subcolloidal particles) is deemed not to be a reasonable description of molecular sieve growth. The conclusion that the colloidal crystals are stable with respect to aggregation is supported by experimental observations. The ideas presented in this study are based upon crystallization of molecular sieves from clear solutions in the presence of quaternary ammonium cations that play a significant role in the stabilization of the colloidal crystals. Extension of the ideas presented shows that the extended DLVO theory is equally applicable to wholly inorganic heterogeneous systems.

Zeolite macrostructures in the form of silicalite-1 spheres were prepared using anion exchange resin beads as shape directing macrotemplates. The resin was removed after the synthesis by combustion leaving solid spherical particles identical in shape and size to the original resin beads. The formation of the silicalite-1 spheres was studied by Raman spectroscopy, X-ray diffraction, scanning electron microscopy and nitrogen adsorption measurements. Samples prepared for different times of treatment and at two different temperatures, 100°C and 165°C, were investigated. The spheres obtained for short treatment times consist of amorphous silica, which after longer hydrothermal treatment in the presence of TPA cations is partially or entirely transformed into an MFI structure. A single treatment at 100°C resulted in hard silicalite-1 spheres of low crystallinity, whereas fully crystalline spheres could be obtained by a treatment at the higher temperature. However, the spheres prepared at 165°C have inferior mechanical properties and can even loose their shape at certain conditions. A better control of both hardness and crystallinity was achieved by using a two-step synthesis procedure, where a treatment at 100°C was followed by a treatment at 165°C.

Zeolite beta was crystallized from clear homogeneous solutions within the pores of anion exchange resin beads. The organic macrotemplate was then removed by combustion leaving stable macrospheres of zeolite beta. The zeolite beta crystallization within the resin beads was investigated by X-ray diffraction, Raman spectroscopy, SEM and nitrogen adsorption measurements. Crystallization within the macrotemplates was compared with the crystallization from bulk solution. The influence of the resin beads on the crystallization process was investigated by increasing the amount of ion exchanger present during synthesis and also by preparing bulk samples in the absence of macrotemplates.

Silicalite-1 microspheres were prepared by a novel method based on the use of anion exchange resins as shape-directing macro-templates. In a first step, spherical beads of the ion exchange resin were hydrothermally treated in a silicalite-1 synthesis solution. This resulted in the crystallization of silicalite-1 in the pores of the resin and the formation of a silicalite-1/resin composite material. The organic ion exchange resin was then removed by calcination leaving self-bonded spherical particles of silicalite-1. The influence of the type of ion exchange resin, the treatment time as well as the weight ratio between synthesis solution and resin on the properties of the resultant materials were investigated. The silicalite-1 containing microspheres were characterized by XRD, Raman spectroscopy, SEM, nitrogen adsorption and microhardness measurements.

Thin and continuous silicalite-1 films with controllable thickness between 200 and 800 nm were synthesized on steel supports by a method employing seeding. A variety of steel types ranging from ordinary carbon steel to highly corrosion resistant steel were used. Continuous transparent silicalite-1 films were formed on all steel types after zeolite synthesis. The type of steel did not affect the film morphology, the thickness or the preferred orientation of the crystals. The (5 0 1) reflection dominates in the XRD pattern for thin films whereas the (1 0 1) and (3 0 3) reflections dominate for thicker films. The silicalite-1 films on various stainless steel supports were stable during calcination, whereas a relatively thick magnetite/hematite film formed on carbon steel upon calcination and the silicalite-1 film detached.

Growth of oriented films of epitaxial MFI overgrowths by the in situ method was studied by SEM, TEM and powder XRD. By using a short hydrothermal treatment, it was possible to grow well-defined, b-oriented ZSM-5 films on polished quartz substrates. It was found that these b-oriented precursor ZSM-5 films grew along the b-axis in an aluminum free silicalite-1 synthesis mixture. Simultaneously, 90° rotational intergrowths formed on top of the b-oriented crystals. Upon further growth in several short synthesis steps, the 90° rotational intergrowths formed an a-oriented silicalite-1 film on top of the first b-oriented film. Only very weak reflections representing other crystallographic planes than (h 0 0) and (0 k 0) are observed by XRD in these samples, which shows that all crystals are a- or b-oriented. Continuous crystals, extending from the support to the top surface of the film was observed by electron microscopy.

Films of epitaxial MFI overgrowths, i.e. ZSM-5 films covered with silicalite-1, with crystals extending from the substrate to the top surface, were synthesized using a seeding method with acid leaching between the synthesis of the MFI layers. The films were characterized by SEM, TEM, XRD and XPS. When acid leaching was omitted, secondary nucleation of silicalite-1 on the ZSM-5 film resulted in a sandwich film with discontinuous crystals. When the precursor ZSM-5 film was acid leached and the surface Si/Al ratio increased from 23 to 47, the crystals in the precursor film grew epitaxially upon treatment in a silicalite-1 synthesis mixture. It was thus revealed that reduction of the aluminum content at the external surface of ZSM-5 may be important for the successful synthesis of epitaxial MFI overgrowths. Alternatively, acid leaching may provide a cleaner surface, and facilitate epitaxial growth.

Zeolite NaX@NaA core-shell microspheres were prepared via a post-treatment secondary growth of zeolite NaA films on outer surface of binderless zeolite NaX microspheres. The obtained core-shell microspheres were composed of intergrown octahedral NaX particles inside, with particles size of ca. 500–750 nm, and continuous zeolite NaA films on the outer surface with the thickness of about 2 μm. Higher CO2 separation performance was observed for the core-shell microspheres comparing to the parental binderless zeolite NaX microspheres. The ideal separation factors of zeolite NaX@NaA core-shell microspheres for CO2/CH4 and CO2/N2 were 13 and 47, and the adsorption selectivities for the corresponding binary mixtures were 308 and 923, significantly higher than the binderless zeolite NaX microspheres of 9 and 19 as well as 264 and 735, respectively. After K+ ion exchanging, the core-shell zeolite microspheres have even higher adsorption selectivities of 326 and 1109 for CO2/CH4 and CO2/N2 binary mixtures. The crushing strength of the binderless zeolite NaX microspheres was increased from 0.46 MPa to 3.42 MPa after the secondary growth. In addition, the growth of zeolite A film was resultant from interzeolite conversion and the interzeolite conversion was investigated by the conversion of zeolite NaX to NaA crystals in NaA membrane synthesis gel.

In situ hydrolysis-gelation-hydrothermal (HGH) synthesis of tetraethylorthosilicate (TEOS) technique was developed to prepare hollow zeolite NaA/chitosan composite microspheres. The chitosan solution coated calcium alginate microspheres served as template to generate hollow structure, which were pre-modified by oleic acid and coated by TEOS. Furthermore, the calcium alginate microspheres were prepared by a simple homemade double T-junction mixer. During the hydrothermal process, the TEOS hydrolyzed and provided silica source for the zeolite NaA shell, meanwhile the inner calcium alginate microsphere core dissolved by the alkaline synthesis mixture and left the hollow structure. The obtained products were characterized by XRD, FT-IR, SEM, TG et al. techniques. The preparation method for calcium alginate microspheres template was simple and the preparation process had no NaA crystal seeds been involved. The hollow size could be adjusted by controlling the synthesis parameters of calcium alginate/chitosan microspheres. In addition, the functional magnetic γ-Fe₂O₃ nanoparticles could be introduced into the cavity during synthesis of calcium alginate/chitosan microspheres and guest magnetic γ-Fe₂O₃ nanoparticles had no effect on the properties of host zeolite NaA. The obtained functional magnetic hollow NaA/chitosan microspheres had decent adsorption performance for Cu²⁺ ions and were easy to recycle.

In the present work, zeolite membranes were for the first time evaluated for separations at cryogenic temperatures. MFI membranes were evaluated with a feed of synthetic air, at varying feed pressures between 1– 5 bar and a sweep stream of helium at a constant pressure of 1 bar for temperatures in the range 77 to 110 K. When the feed pressure was 1 bar, the highest O2/N2 separation factor was 3.9, corresponding to a separation selectivity of 4.1, with an oxygen permeance of 6.7×10-7 mol m-2 s-1 Pa-1 at the optimum temperature 79 K. This membrane performance is just above the upper bound in the 2008 Robeson selectivity- permeability plot for polymeric membranes. As the feed pressure increased, the maximum separation factors for O2/N2 decreased while the optimum separation temperatures increased. It is inferred that the separation is governed by condensation and effective transport of oxygen in the zeolite pores under these conditions. However, the adsorption of nitrogen, and thereby the transport of nitrogen, likely increases as the pressure is increased, which reduce the selectivity. To test this hypothesis, the feed was diluted with 33% helium and the total feed pressure was maintained at 1 bar, corresponding to a partial pressure of air of 0.66 bar. In this case, the maximum separation factor increased to 4.3, which supports the proposed separation mechanism.