ZSM-5 Crystals Research Articles

Phase Transformation of Rice Husk Ash in the Synthesis of ZSM-5 without Organic Template

Phase transformation of rice husk ash in the synthesis of ZSM-5 without organic template at various crystallization times has been studied. Zeolite has been synthesized using the hydrothermal method at 175 °C with molar ratio 10Na2O : 100SiO2 : 2Al2O3 : 1800H2O with addition of silicalite-1 as seed. Solids were characterized using X-ray diffraction (XRD), infrared (IR) spectroscopy and scanning electron microscopy (SEM) techniques. Analysis of the results of XRD and IR spectroscopy indicated that ZSM-5 crystalstarted to form at 12 h of crystallization time, reaching high crystallinity after 24 h. With a crystallization time of more than 48 h, the ZSM-5 crystals had completely transformed into more stable quartz phase. Results indicated that phase transformation has occurred, in which an amorphous phase of rice husk ash has been transformed to ZSM-5 crystal phase during the early crystallization stage and continued to transform to disordered α-cristobalite phase and lastly quartz phases. SEM showed that the morphology of the ZSM-5 crystal was of an irregular hexagonal shape with particle size distribution around 3-7 μm.

Synthesis of highly b-oriented ZSM-5 membrane on a rough surface modified simply with TiO2 by in situ crystallization

A simple, reliable and reproducible approach for the fabrication of highly b-oriented ZSM-5 zeolite membranes on rough surface is presented. The approach consists of depositing a TiO2 intermediate layer on the rough surface of substrate, followed by UV irradiation, and subsequently in situ crystallization on the TiO2 modified rough surface. The TiO2 interlayer combined UV irradiation provides a smooth and high Ti–OH density surface for the growth of b-oriented ZSM-5 crystals. By comparing the morphology of zeolite membranes on Al2O3, SiO2, ZrO2, and TiO2, the impacts of smoothness, dispersion force between the zeolite crystal phase and substrate, and density of surface hydroxy on the formation of a highly b-oriented and continuous ZSM-5 membrane have been investigated. A smooth surface rich in Ti-OH was helpful for the continuous and uniform spread of the synthesis solution on the support, resulting in the oriented nucleation and accelerated growth of zeolite crystals, which formed the highly b-oriented and covered ZSM-5 membrane.

Framework Sites Preferred by Aluminum in Zeolite ZSM-5. Structure of a Fully Dehydrated, Fully Cs+-Exchanged ZSM-5 Crystal (MFI, Si/Al = 24)

The structure of a single crystal of fully Cs+-exchanged, fully dehydrated zeolite ZSM-5 (MFI, Cs3.8Al3.8Si92.2O192, Si/Al = 24) has been determined crystallographically using synchrotron X-radiation in the orthorhombic space group Pnma (a = 20.070(1), b = 19.913(1), c = 13.389(1) Å) and refined to R1 = 0.076 with 5443 reflections. A total of 3.5(2) Cs+ ions were found per unit cell scattered among 11 crystallographically distinct positions. Three are within the intersection volume (the volume that is both in the zigzag channel (ZC) and in the straight channel (SC)), two are in the cove at the side of the intersection volume, one is in the 10-ring that connects two intersection volumes, four lie elsewhere in 10-rings at the surface of the intersection volume, and one is in the unique segment of the ZC that is not a part of any of the above. The two most highly populated positions, with a total occupancy of 1.09(12) Cs+ ions per unit cell, are in the cove at the side of the intersection volume. The preference of Al atoms among the T sites of the ZSM-5 framework is identified from Cs+ occupancies and Cs–O bond lengths. Using all such bonds shorter than 3.35 Å, the preferred order for Al among the T sites appears to be T7 (most preferred) > T10 > T8 > T2. T7 is in the cove and on the wall of the intersection volume; T10 is in the cove and on the wall of just the ZC. A small Al presence is seen at T11, some may be present at T12, but there is no indication that Al atoms are present at T1, T3, T4, T5, T6, nor T9, fully half of the T positions in the crystal studied.

High Energy Ion Irradiation-Induced Ordered Macropores in Zeolite Crystals

The present study demonstrated the possibility to form a secondary system of parallel macropores in zeolite crystals. The secondary pore formation was predetermined by the creation of defect zones in ZSM-5 crystals. A high energy (238)U ion beam was employed to form latent tracks in zeolite crystals, which were further subjected to attack with diluted HF solution and thus developed to uniformally sized macropores. The selective extraction of material from latent tracks was due to the higher etching velocity of highly agitated zones created by heavy ion bombardment. The combination of complementary methods unambiguously demonstrated the formation of hierarchical zeolite material comprising parallel macropores that extended through the entire crystal. The catalytic tests revealed improved activity at retained selectivity in the reaction of m-xylene conversion. The possibility to control the number of macropores per unit of crystal surface and thus the catalytic performance of the material was demonstrated. This model material is expected to bring better understanding to the effect of a secondary pore system in the catalytic performance of hierarchical zeolites obtained by the top-down or bottom-up approach.

Methanol to Gasoline-Range Hydrocarbons: Influence of Nanocrystal Size and Mesoporosity on Catalytic Performance and Product Distribution of ZSM-5

Improvement of synthesis methods for ZSM-5 zeolite, as a heteregeneous catalyst, is essential for a wide variety of different reactions in the chemical industry. Decreasing zeolite crystal size and introducing mesoporosity into the zeolite structure can improve its performance in catalytic reaction through decreasing the micropore diffusion path-length and increasing the external surface area. In this study, three different ZSM-5 zeolites (Nano-ZSM-5, Meso-ZSM-5, and Con-ZSM-5) were prepared by a single-templating procedure, and the reaction of methanol to gasoline-range hydrocarbons was evaluated over synthesized ZSM-5 crystals in a fixed-bed continuous flow reactor. Good correlation was observed between catalytic performance, product distribution, mesoporosity, and crystal size of ZSM-5 zeolites. Both nanocrystal and mesoporous ZSM-5 zeolites showed long-term catalytic stability compared with the conventional one. In contrast to conventional ZSM-5 catalyst, the nanocrystal and mesoporous ZSM-5 catalysts...

Synthesis of mesoporous ZSM-5 zeolites through desilication and re-assembly processes

ZSM-5 zeolite crystals with secondary mesopores were synthesized by alkaline desilication and surfactant-induced re-assembly of dissolved species (i.e., silicates, aluminosilicates and zeolite crystal fragments) originating from the parent ZSM-5 crystals. The meso-zeolite products exhibit a dual-mesopore structure in which the smaller mesopores (ca. 3 nm) are attributed to surfactant-induced micelle formation involving dissolved species, and larger mesopores (ca. 10–30 nm) result from desilication processes occurring under the alkaline reaction conditions. The external surface area (i.e., the surface area due to mesopores, macropores and the external particle surface) of the meso-zeolite materials depends on the Si/Al ratio, the hydroxide concentration and the presence of surfactant, and it reaches values as high as 327 m 2 g −1 when a surfactant is used. The crystallinity of the highest surface-area meso-zeolite is well preserved, maintaining values of ca. 83% (on the basis of micropore volume) or ca. 77% (on the basis of X-ray diffraction intensities) of the parent zeolite structures. Further physicochemical characterization by 27Al and 29Si magic-angle-spinning solid-state NMR spectroscopy, scanning and transmission electron microscopy, temperature-programmed ammonia desorption measurements, and inductively coupled plasma elementary analysis support the hypothesis that re-assembly of dissolved species of zeolite crystals occurred by surfactant-induced micellization, resulting in the high external surface area of the meso-zeolite materials.

Yield of gasoline-range hydrocarbons as a function of uniform ZSM-5 crystal size

Abstract Uniform ZSM-5 nanocrystals were synthesized by a single-templating procedure. The samples were then characterized by a variety of physical techniques such as XRD, SEM, BET, ICP and TPD. The dehydration of methanol over synthesized ZSM-5 zeolite was studied in a fixed-bed continuous flow reactor at 370 °C and WHSV of 2.6 gg −1 h under ambient pressure. The effect of crystal size of zeolite catalysts on product distribution in methanol dehydration reaction was investigated. Good correlation was observed between catalytic performance, product distribution and size of ZSM-5 crystals. It was found that the decrease in crystal size significantly influences light olefins (ethylene and propylene) and paraffins (C 1 –C 4 ) selectivity in methanol dehydration reaction. Furthermore, nanocrystal ZSM-5 showed long-term catalytic stability compared with conventional ZSM-5 provided that the reaction activity is strongly dependent on the crystal size in methanol dehydration process. The results indicated that crystal size significantly affects the catalyst lifetime and hydrocarbon distributions in product stream. Based on the obtained results, it is concluded that the use of uniform ZSM-5 nanocrystals improves the yield of propylene and alkyl aromatics in methanol conversion reaction at mild conditions.

Carbon Nanotube Templated Growth of Nano-Crystallinity ZSM-5

MFI-type(ZSM-5) zeolite nanocrystals with SiO2/Al2O3ratios of 100 has been synthesized through crystallization of gel in mesoporous system of carbon nanotubes(CNTS) with internal diameter of 20~30nm. Investigation by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscope (TEM) and scanning electron microscope (SEM) shows that the nanocrystals possess the typical nanosized zeolites structural characteristics which is different from those of microsized zeolites. Compared with those of the corresponding sample synthesized in hydrothermal system, the bands of the nanosized sample are shifted slightly to lower or higher wavenumbers. The TEM images of the purified carbon nanotubes and nanosized ZSM-5 crystals after the removal of the carbon matrix suggest that clean and homogeneous carbon nanotubes have internal diameters of approximately 20~30 nm and the most crystal sizes are in the range 30~60nm. The SEM photograph verifies the existing of nanosized ZSM-5.

Growth of ZSM-5 crystals within hollow β-zeolite

Abstract A zeolite composite composed of ZSM-5 and β-zeolites has been synthesized by a procedure of the nucleation and crystallization of ZSM-5 zeolite in the hollow β-zeolite. The property of β-zeolite crystals with aluminum-poor interior and aluminum-rich outer rim results in silicon extraction favorably in the aluminum-poor bulk rather than the aluminum-rich external surface. Subsequently, alkaline treatment of β-zeolite crystals during the second-step synthesis leads to a preferential dissolution of the aluminum-poor center and the formation of hollow β-zeolite crystals. ZSM-5 zeolite crystals are therefore embedded and grown within the hollow β-zeolite. The catalytic activities of Co-Hβ, Co-HZSM-5 and Co-HZSM-5/BEA are investigated during the reaction of methane catalytic reduction NO in the presence of O2.

In Situ Recrystallization of Silica Template for Synthesis of Novel Microporous ZSM-5/Hollow Mesoporous Carbon Composites

Silica-based nanocasting synthesis of a nanostructured carbon replica inevitably involves the disposal of silica waste and toxic etchant after the time-consuming and costly etching processes for selective removal of silica template from a carbon/silica composite to produce the silica-free carbon replica, not only resulting in chemical waste, but also posing serious environmental concerns. Instead of removal of the silica template, the in situ recrystallization transformation of the silica into more useful functional nanostructured silica offers an attractive alternative to the problem of handling silica waste and toxic etchants. In this work, the novel composites composed of microporous zeolite ZSM-5 crystals and hollow core-mesoporous shell carbon (HCMSC) capsules are synthesized for the first time by such transformation process of sacrificial silica template in the carbon/solid core-mesoporous shell silica (SCMSS) composite through hydrothermal process under alkaline condition. Compared to the commercia...

Bubbling Reactor Technology for Rapid Synthesis of Uniform, Small MFI-Type Zeolite Crystals

MFI-type zeolite is an important family of materials used in today’s industries as catalysts and adsorbents. Preparation of this type of zeolite material as uniform and pure crystals of sizes from tens of nanometer to hundreds of nanometer are not only desired by current catalytic and adsorption processes for enhanced reaction kinetics and/or selectivity, but also much needed by some new applications, such as CO2 capture adsorbents and composite materials. However, it has been a major challenge in the zeolite synthesis field to prepare small crystals of MFI-type zeolite over a range of Si/Al ratio with very high throughput. In this work, a gas-bubbling flow reactor is used to conduct hydrothermal growth of the zeolite crystals with controllable Si/Al ratio and crystal sizes. Distinctive, uniform ZSM-5 crystals are successfully synthesized within two hours of reaction time, exceptionally short compared to the conventional synthesis process. The crystals are small enough to form a stable milk-like suspension in water. The Si/Al ratio can be controlled by adjusting the growth solution composition and reaction conditions over a range from about 9 to infinity. Characterization by SEM/EDS, XRD, TEM, N2 adsorption/desorption, and NMR confirms ZSM-5 crystal structures and reveals presence of meso-porosity in themore » resulting crystals.« less

CO 2 separation using PDMS/ZSM-5 zeolite composite membrane

This study demonstrates the successful implications of hydrothermal and secondary growth techniques for synthesis of high property Silicalite-1 and ZSM-5 zeolites. To prepare ZSM-5 a membrane, the nanosized Silicalite-1 powder was first synthesized as a seed from a clear solution. The effects of variations in the synthesis time, aluminum content and the number of seeding on the characteristics of ZSM-5 zeolite were studied. It was found that three subsequent seeding steps enhance significantly quality of membranes surface morphology which led to regular growth of ZSM-5 crystals. The zeolite membranes produced were characterized using SEM, TEM, TGA, DSC and N 2 adsorption techniques. At room temperature, permeance of CO 2 was higher than those of N 2 and CH 4 and the ideal selectivities for CO 2/N 2 and CO 2/CH 4 were 9.6 and 6.5 at mean pressure of 0.5 bar, respectively. Improved zeolite membrane was fabricated by dip-coating of membrane in PDMS solution. Ideal selectivity of produced composite membrane for CO 2/N 2 and CO 2/CH 4 was obtained as 21 and 14.2, respectively. Ideal selectivity of CO 2/N 2 and CO 2/CH 4 and CO 2 permeance decreased with mean pressure in the ZSM-5 zeolite membranes whereas, for composite membrane the selectivities and CO 2 permeance increased by mean pressure due to adsorption effect in the range of 0.5–1.5 bar and then remained constant by increasing of mean pressure.

ZSM-5 and ferrierite single crystals with lower Si/Al ratios: Synthesis and single-crystal synchrotron X-ray diffraction studies

Less twinned and high Al-containing ZSM-5 (MFI, Al 3.8Si 92.2O 192, Si/Al = 24.1) and high Al-containing ferrierite (FER, Al 2.0Si 34.0O 72, Si/Al = 16.7) large single crystals were synthesized by hydrothermal methods using mixed organic structure-directing agents and confirmed by single-crystal X-ray diffraction and SEM-EDX techniques. These large zeolite single crystals with an average size of 100 and 280 μm on an edge for ZSM-5 and ferrierite, respectively, were found to exhibit good qualities for potential use in advanced applications.

In situ synthesized Cu-ZSM-5/cordierite for reduction of NO

ZSM-5 zeolites were directly synthesized on the surface of honeycomb cordierite substrates by hydrothermal method and certified by XRD and SEM techniques; the adhesion of ZSM-5 coatings was evaluated by ultrasonic vibration. Cu-ZSM-5/cordierite monolithic catalyst was prepared by ion-exchange and impregnation method and applied for the selective catalytic reduction (SCR) of NO by NH 3 using a simulated diesel exhaust. The results show that the cordierite surface is almost completely covered by ZSM-5 crystals and the crystallization time greatly impacts the loadings and adhesion of ZSM-5 coatings on substrate, the NO x removal rate over Cu-ZSM-5/cordierite is above 90% in a temperature range of 240–480 °C. Moreover, Cu-ZSM-5/cordierite prepared by different methods shows a wide temperature window (240–540 °C) with high NO removal activities.

Hierarchical zeolites prepared by organosilane templating: A study of the synthesis mechanism and catalytic activity

The crystallization of hierarchical ZSM-5 in the presence of the organosilane octadecyl-dimethyl-(3-trimethoxysilyl-propyl)-ammonium chloride as the mesoporogen was investigated as a function of time and temperature. The synthesis by this method proceeds in two steps. The rapid formation of a predominantly amorphous disordered mesoporous aluminosilicate precursor phase is followed by the formation of globular highly mesoporous zeolite particles involving dissolution of the precursor phase. It is difficult to completely convert the initial phase into the final hierarchical zeolite. This limits the amount of aluminium built into the MFI network and the resulting Brønsted acidity. In the presence of iron, more crystalline hierarchical zeolite is obtained. These Fe-containing zeolites are excellent catalysts for the selective oxidation of benzene to phenol. Their hierarchical pore structure leads to higher reaction rates due to increased mass transfer and increased catalyst longevity despite more substantial coke formation.

Architecture‐Dependent Distribution of Mesopores in Steamed Zeolite Crystals as Visualized by FIB‐SEM Tomography

Break on through: Steaming-induced mesopores of individual ZSM-5 crystals were studied by a combination of focused ion beam (FIB) and scanning electron microscopy (SEM) tomography (see picture). In this manner, quantitative insight into the width, length, morphology, and distribution of mesopores generated within zeolite crystals has been obtained. Keywords:crystal intergrowth;scanning probe microscopy;mesoporosity;tomography;zeolites

New insight in the template decomposition process of large zeolite ZSM-5 crystals: an in situUV-Vis/fluorescence micro-spectroscopy study

A combination of in situ UV-Vis and confocal fluorescence micro-spectroscopy was used to study the template decomposition process in large zeolite ZSM-5 crystals. Correlation of polarized light dependent UV-Vis absorption spectra with confocal fluorescence emission spectra in the 400-750 nm region allowed extracting localized information on the nature and amount of chemical species formed upon detemplation at the single particle level. It has been found by means of polarized light dependent UV-Vis absorption measurements that the progressive growth of molecules follows the orientation of the straight channels of ZSM-5 crystals. Oligomerizing template derivatives lead to the subsequent build-up of methyl-substituted benzenium cations and more extended coke-like species, which are thermally stable up to ∼740 K. Complementary confocal fluorescence emission spectra showed nearly equal distribution of these molecules within the entire volume of the thermally treated zeolite crystals. The strongest emission bands were appearing in the orange/red part of the visible spectrum, confirming the presence of large polyaromatic molecules.

Preparation of discrete colloidal ZSM-5 crystals with high Al-content

A new method for synthesis of discrete colloidal ZSM-5 particles with SiO2/Al2O3 M ratios as low as 30 and sizes .4–1 micrometer has been developed. The relation between the synthesis parameters and synthesis yield, crystal structure, crystallinity, particle size and morphology was investigated. The synthesis yield increases and the deviation of the SiO2/Al2O3 ratio in the product from that in synthesis mixture decreases with increasing autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that temperature determines the lower limit of the SiO2/Al2O3 ratio. The SiO2/Al2O3 ratio in the synthesis mixture decreases with autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that the temperature determines the lower limit of SiO2/Al2O3 ratio. Synthesis mixture, aimed to yield a high SiO2/Al2O3 ratio, gives smaller zeolite crystals, higher specific surface areas, higher geometric areas (external surface area of the crystals) and a more oval crystal shape compared with lower ratios, synthesised at the same temperature. Higher autoclave temperature during the synthesis gives larger zeolite crystals and a more hexagonal crystal shape compared with zeolites synthesised at lower temperatures, for the same SiO2/Al2O3 ratios.

Rapid crystallization and morphological adjustment of zeolite ZSM-5 in nonionic emulsions

Zeolite ZSM-5 was synthesized for the first time in a nonionic emulsion composed of polyoxyethylated alkylphenol, butanol, cyclohexane and tetraethylammonium hydroxide (TEAOH)-containing zeolite synthesis mixture. The crystallization kinetics in the emulsion was investigated and the ZSM-5 product was characterized in detail by XRD, SEM, FT-IR, TG, N 2 adsorption and CHN analysis techniques. Compared with the conventionally hydrothermal synthesis with the same structure directing agent TEAOH, the emulsion system allows rapid crystallization of ZSM-5. The ZSM-5 product exhibits unusual agglomerated structure and possesses larger specific surface area. The FT-IR, TG results plus CHN analysis show the encapsulation of a trace of emulsion components in the emulsion ZSM-5. Control experiments show the emulsion system exerts the crystallization induction and morphological adjustment effects mainly during the aging period. The effects are tentatively attributed to the confined space domains, surfactant–water interaction as well as surfactant-growing crystals interaction existing in the emulsion.

Synthesis of zeolite crystals with unusual morphology: Application in acid catalysis

ZSM-5 zeolite nanocrystals having a rectangular morphology (French fries-like) and a size comprised between 50 and 100 nm were prepared using cheap sugar cane bagasse as a sacrificial template. Two sugar cane biomass types, un-treated and acid hydrolyzed bagasse, were used. A relationship has been established between the chemical composition of the sacrificial vegetal and the morphology of grown zeolite crystals. Aligned zeolite nanocrystals were allowed to grow on non hydrolyzed sugar cane substrate, using a combination of supramolecular templating and conventional self-assembly of template cations and silica species. The latter material allowed enhanced diffusional properties in comparison with purely microporous zeolite, as well as ZSM-5 crystals grown on hydrolyzed bagasse. Their catalytic behavior in n-hexane cracking reaction led to a higher selectivity toward light olefins. The double novelty consists in the manufacture of hierarchical zeolite microspheres (diameter about 1 μm) formed by the self-aggregation of rectangular subunits. In addition, a renewable vegetal source can be used as a supramolecular template in replacement of expensive polymers.