ZSM-5 Zeolite Crystals Research Articles

Synthesis of Monolith Hierachical ZSM-5 Zeolite Composed of Nanocrystals by Vapor-phase Transformation Method

A monolith ZSM-5 composed of nano-sized MFI crystals was prepared from a dry gel by a vapor-phase transformation method, in which the dry gel was obtained from a mixture of sodium carboxymethylcellulose and a precursor yielding ZSM-5 zeolite crystals. The as-synthesized samples were characterized by X-ray diffraction(XRD), scanning electron microscope(SEM), N2 adsorption-desorption, in-situ IR spectra of pyridine and FT-IR. Organic Sior/and Al-species replace the classic inorganic Si- or/and Al-species to take part in the construction of MFI zeolite frameworks. And the long chain organic groups, which connect with the Si- and Al-species, disturb the normal growth of the zeolites crystals in the manner of the so called "bond block". The evenly nano-sized zeolite crystals with the sizes of 100–150 nm are therefore formed and then subsequently self-assembly form a monolith ZSM-5. A mesoporous system which centers around 2–20 nm is therefore introduced into the as-synthesized hierachical zeolites samples. As compared with the references catalysts, the monolith ZSM-5 zeolite composed of nano-sized crystals displays an enhanced conversion of isopropylbenzene because of the dramatically increased external surface areas and mesopores volume as tested by the catalytic cracking of isopropylbenzene.

Performance of zeolite membrane (ZSM-5/γ-Alumina) in the oil/water separation process

There are several technologies for the treatment of oily wastewater generated by the oil industry, not only to separate the emulsified oil in water, but also to reduce its concentration in the aqueous effluent. Among the processes of separation, the separation using membranes should be highlighted when they become an effective material and it also resistant to high temperatures, have good corrosion resistance, easy to clean, and have long life operation, among others. This work aims to synthesize the material (ZSM-5, γ-alumina membrane, and zeolite membrane ZSM-5/γ-alumina) and to evaluate the membranes in the oil/water separation in a continuous flow system. From the XRD results of the individual materials, it can be observed the formation of all the characteristic peaks for each material. The EDX analysis of zeolite ZSM-5 showed the formation of this material with a Si/Al = 19. From the SEM image of these materials, it can be seen that the surface of the γ-alumina is completely covered with ZSM-5 zeolite crystals. The oil/water removing, using ZSM-5 γ-alumina membrane, showed high retention of the oil, obtaining a higher performance in relation to γ-alumina membrane. This reveals that the insertion of ZSM-5/γ-alumina in the material makes that this new material acquires a lower porosity, obtained by decreasing the passage of oil molecules through the membrane structure.

Dielectric and ethanol sensing studies on synthesized nano-ZSM-5 zeolite

Nano-sized ZSM-5 zeolite crystals are synthesized without organic template using microwave assisted hydrothermal technique. The synthesized zeolite is then characterized by various techniques like X-ray diffraction, Fourier transform infrared spectroscopy and thermo gravimetric analysis. X-ray diffraction profile confirms that the synthesized zeolite structure is of ZSM-5 and grain size of synthesized zeolites is found to be about 30 nm. Fourier transform infrared spectroscopy shows the presence of T–O–T link of zeolite structure. The thermal stability of ZSM-5 is studied by using simultaneous thermo gravimetric analyzer. Screen printed thick films are prepared using the synthesized nano-ZSM-5 zeolite as a functional material. Atomic force microscopy reveals the topography of thick film. Study on ethanol sensing characteristics of zeolite thick films has shown that the film can be used as an ethanol sensor at an operating temperature of 135 °C with a quick response of 150 s. Saturation limit for the film is observed to be very low.

Synthesis of NiMo hydrodesulfurization catalyst supported on a composite of nano-sized ZSM-5 zeolite enwrapped with mesoporous KIT-6 material and its high isomerization selectivity

A novel composite material ZSM-5/KIT-6 (ZK-W) was synthesized by enwrapping nano-sized ZSM-5 zeolite crystals with mesoporous KIT-6 silica. This composite was used as catalyst support for NiMo sulfide in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The NiMo/ZK-W catalyst showed the highest HDS activity and its 4,6-DMDBT conversion was about double that of a conventional NiMo/Al2O3 catalyst at 320°C, 4.0MPa, and LHSV of 150h−1 and on the basis of sulfur. The superior catalytic performance of NiMo/ZK-W is related to the synergistic effect of the excellent diffusion through the hierarchical porous structure and the suitable Brønsted acid sites. 3,6-DMDBT and 3,7-DMDBT, two isomers of 4,6-DMDBT, were identified simultaneously for the first time in the HDS products of 4,6-DMDBT over the NiMo/ZK-W catalyst. The NiMo/ZK-W catalyst exhibited a superior isomerization ability, and 4,4′-dimethylbiphenyl was the main product, indicating that the isomerization pathway is the main reaction route. A new reaction network of 4,6-DMDBT HDS over NiMo/ZK-W catalyst was proposed.

Amphiphilic Organosilane-directed Synthesis of Mesoporous ZSM-5 Zeolite Crystals with a Chain-like Morphology

Abstract Mesoporous zeolites with a chain-like morphology were synthesized by adding a rationally designed carbamate-linked organosilane to conventional alkaline zeolite synthesis mixtures. The structure was confirmed by a complementary combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption measurements. The XRD patterns and SEM images of the samples acquired at different crystallization time clearly showed the change of crystallinity and the forming process of the morphology.

Recent advances in secondary ion mass spectrometry of solid acid catalysts: large zeolite crystals under bombardment

This Perspective aims to inform the heterogeneous catalysis and materials science community about the recent advances in Time-of-Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) to characterize catalytic solids by taking large model H-ZSM-5 zeolite crystals as a showcase system. SIMS-based techniques have been explored in the 1980-1990's to study porous catalyst materials but, due to their limited spectral and spatiotemporal resolution, there was no real major breakthrough at that time. The technical advancements in SIMS instruments, namely improved ion gun design and new mass analyser concepts, nowadays allow for a much more detailed analysis of surface species relevant to catalytic action. Imaging with high mass and lateral resolution, determination of fragment ion patterns, novel sputter ion concepts as well as new mass analysers (e.g. ToF, FTICR) are just a few novelties, which will lead to new fundamental insight from SIMS analysis of heterogeneous catalysts. The Perspective article ends with an outlook on instrumental innovations and their potential use for catalytic systems other than zeolite crystals.

Intergrowth of Components and Ramps in Coffin-Shaped ZSM-5 Zeolite Crystals Unraveled by Focused Ion Beam-Assisted Transmission Electron Microscopy

Scanning electron microscopy, focused ion beam (FIB), and transmission electron microscopy are combined to study the intergrowth of 90° rotational components and of ramps in coffin-shaped ZSM-5 crystals. The 90° rotational boundaries with local zig-zag features between different intergrowth components are observed in the main part of crystal. Also a new kind of displacement boundary is described. At the displacement boundary there is a shift of the unit cells along the boundary without a change in orientation. Based on lamellae prepared with FIB from different positions of the ramps and crystal, the orientation relationships between ramps and the main part of the crystal are studied and the three-dimensional morphology and growth mechanism of the ramp are illustrated.

Synthesis and characterization of high siliceous ZSM-5 zeolite from acid-treated palygorskite

High siliceous ZSM-5 zeolite was successfully synthesized from palygorskite (PAL) via an in situ hydrothermal method by using acid-treated PAL as silica and aluminum sources. The effects of crystallization temperature, crystallization time, Na2O/SiO2 molar ratio, and SiO2/Al2O3 molar ratio on the crystallization of ZSM-5 zeolite were studied as well as the crystallization mechanism. Investigations on the crystallization mechanism of ZSM-5 zeolite indicated that the acid-treated PAL composed of amorphous silica was partially dissolved and then converted into aluminosilicate in the alkaline solution. ZSM-5 nucleus grew well to crystalline ZSM-5 zeolite after consuming the aluminosilicate and acid-treated PAL. The extra NaOH and aluminum source were the key factors of the synthesis of ZSM-5 zeolites from acid-treated PAL. High Na2O/SiO2 molar ratio and the addition of aluminum were unfavorable for the formation of ZSM-5 zeolite. A part of Al atoms in PAL entered into the frameworks of zeolites, resulting in the formation of high siliceous ZSM-5 after hydrothermal treatment. High crystallization temperature and long crystallization time were beneficial for the transformation of PAL into ZSM-5 zeolite as well as the increase of zeolite crystallinity.

A fast organic template-free, ZSM-11 seed-assisted synthesis of ZSM-5 with good performance in methanol-to-olefin

This work demonstrated a novel and efficient route for preparing ZSM-5 zeolite by adding ZSM-11 seeds in a template-free system. Compared to conventional ZSM-5-seeded synthesis using crystallization time of 36h, ZSM-11 seeds drove the crystallization of ZSM-5 in much shorter time (12–16h). Particularly, as used hierarchical ZSM-11 seeds with intergrowth morphology, numerous small ZSM-5 crystals with size of 1–2μm could be obtained in a very short period (12h). Both the seed and product zeolites were characterized by XRD, XRF, 27Al MAS NMR, SEM, FTIR and N2 adsorption–desorption analysis. It was found that the existence of terminal Si–OH units on the surface of ZSM-11 seed particles was principally responsible for the fast crystallization of target ZSM-5 zeolites. Moreover, the external surface area provided by the seeds played a vital role in accelerating the nucleation rate by offering specific sites for the formation of nuclei. When applied in the methanol to olefins (MTO) reaction, small ZSM-5 crystals obtained in the hierarchical ZSM-11-seeded system exhibited both a high selectivity to C2=–C4= olefins and a low deactivation rate. In general, this green synthesis route gives enlightenment for designing the synthesis of zeolites with good performance by using seed crystals with special properties.

Imaging the effect of a hydrothermal treatment on the pore accessibility and acidity of large ZSM-5 zeolite crystals by selective staining

Confocal fluorescence microscopy has been used in combination with bulky non-reactive dyes (i.e. proflavine, stilbene and nile blue A) and two staining reactions (i.e. fluorescein synthesis and 4-fluorostyrene oligomerisation) to study the effect of steaming on pore accessibility and acidity of large ZSM-5 zeolite crystals. This approach enabled the 3-D visualization of cracks and mesopores connected to the outer zeolite surface as well as mesoporous “cavities” within steamed ZSM-5 zeolite crystals. It has been found that besides the generation of mesoporosity steaming makes the boundaries between the different crystal sub-units accessible for bulky molecules. Additionally, the fluorescein staining reaction reveals prominent formation of structural defects that are connected to the surface of the crystal via the microporous ZSM-5 system and which contain either Brønsted or Lewis acid sites. On the other hand, the 4-fluorostyrene staining reaction shows how mild steaming conditions increase the accessibility towards the Brønsted acid sites, while under severe steaming conditions the Brønsted acidity contained in the internal crystal sub-units is more accessible, although it is preferentially removed close to the surface of the lateral sub-units of ZSM-5 zeolite crystals.

Synthesis of mesoporous ZSM-5 zeolite crystals by conventional hydrothermal treatment

Well-defined ZSM-5 crystals with tablet habit, uniform size, controllable silica/alumina ratio, and high mesoporosity were prepared using conventional hydrothermal treatment under stirring. The key to obtaining high mesoporosity of the crystals was to stir a synthesis mixture containing a relatively high concentration of alumina.

A Simple Route to Synthesize Mesoporous ZSM‐5 Templated by Ammonium‐Modified Chitosan

Uniform mesoporous zeolite ZSM-5 crystals have been successfully fabricated through a simple hydrothermal synthetic method by utilizing ammonium-modified chitosan and tetrapropylammonium hydroxide (TPAOH) as the meso- and microscale template, respectively. It was revealed that mesopores with diameters of 5-20 nm coexisted with microporous network within mesoporous ZSM-5 crystals. Ammonium-modified chitosan was demonstrated to serve as a mesoporogen, self-assembling with the zeolite precursor through strong static interactions. As expected, the prepared mesoporous ZSM-5 exhibited greatly enhanced catalytic activities compared with conventional ZSM-5 and Al-MCM-41 in reactions involving bulky molecules, such as the Claisen-Schmidt condensation of 2-hydroxyacetophenone with benzaldehyde and the esterification reaction of dodecanoic acid and 2-ethylhexanol.

Studies of the effect of synthesis parameters on ZSM-5 nanocrystalline material during template-hydrothermal synthesis in the presence of chelating agent

Nanostructure ZSM-5 zeolite was synthesised via hydrothermal, chelating agent-based method from a mixture with molar composition of 1Al 2 O 3 :46SiO 2 :xTPA:5Na 2 O:1.3Trien:2500H 2 O (x = 0–5.5). The effects of crystallisation time and temperature and template type and content on the synthesised zeolite crystallinity and morphology were investigated. The final products were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Both XRD and SEM results showed that the crystallinity and particle size of the synthesised zeolite increase with increasing crystallisation time for both templates. However, twinned and intergrown crystals of ZSM-5 zeolite with very smooth surfaces were obtained with a crystallisation time of 120 h using a tetrapropylammonium hydroxide (TPAOH) template. Also, the crystallisation temperature had a strong effect on crystallinity and morphology; a highly crystalline ZSM-5 zeolite with twinned crystals was synthesised at 175 °C. Furthermore, the template content had a strong effect on the final product properties. ZSM-5 zeolite with high crystallinity and perfect particles was synthesised at a TPAOH/Si ratio of 0.058. Finally, the effect of the chelating agent (Trien) on crystallinity and morphology of the synthesised ZSM-5 was investigated. ZSM-5 zeolite was synthesised via a chelating agent-based method, with more detailed parametric studies to obtain desired properties in the final product. The effect of the chelating agent (Trien) on crystallinity and morphology of the synthesised ZSM-5 was investigated. Rough and spherical particles were synthesised in the absence of Trien . In contrast, twinned and intergrown shaped crystals with very smooth surfaces were obtained after 120 h of crystallisation at 175 °C in the presence of Trien. ► Nanostructure ZSM-5 zeolite was synthesised via hydrothermal method. ► Trien was used as chelating agent for ZSM-5 zeolite synthesis. ► The effects of synthesis parameters on the zeolite structure were investigated. ► The presence of Trien resulted in the synthesis of twinned and intergrown crystals. ► Rough and spherical particles were synthesised in the absence of Trien.

Unusual Pathway of Crystallization of Zeolite ZSM-5 in a Heterogeneous System: Phenomenology and Starting Considerations

Crystallization of zeolite ZSM-5 from a diluted heterogeneous system (12.5Na2O–Al2O3–8TPABr–60SiO2–4000H2O) was investigated by various experimental methods such as X-ray diffraction (XRD), electron diffraction (ED), infrared spectroscopy (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermo-gravimetric analysis (TGA), particle size analysis (PSA), pH measurement, inductive coupling plasma (ICP) emission spectrometry, and dynamic light scattering (DLS). The crystallization process is characterized by a very long “induction period” (95% of the entire reaction time) and very fast transformation (5% of the entire reaction time) of amorphous to crystalline phase (zeolite ZSM-5) at the end of the crystallization process. Analysis of the obtained results has shown that the crystallization process takes place by a chain of processes: (i) formation of “primary” amorphous aluminosilicate precursor (gel) at room temperatur...

Synthesis of small-sized ZSM-5 zeolites employing mixed structure directing agents

Nano-sized crystals of zeolite ZSM-5 were hydrothermally synthesized using a mixture of two templating agents, tri-ethyl butyl ammonium bromide (TEBA) and ethylene diamine (EDA). Synthesized samples were characterized by XRD, SEM and ammonia TPD. Influences of proportions of the templating agents, silica to alumina ratio (SAR) and crystallization period were have been studied. Crystal morphology and size of the synthesized samples varied with proportions templating agents and SAR. Crystal size in the range of 100–400nm was observed with equimolar templates for an SAR of 200. Crystal size increased to 1 to~3μm with SAR in the range of 400–1200. Crystallization of MFI zeolite in presence of mixed templates was found to pass through an unknown meta-stable intermediate.

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.

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...

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.

Synthesis of hierarchical nanocrystalline ZSM-5 with controlled particle size and mesoporosity

Development of new zeolite based materials is essential for a variety of applications in catalysis, separations, and medicine. Increasing the specific surface area and decreasing the micropore diffusion pathlength in zeolites are important factors for improving the performance of zeolites in catalytic applications and these factors can be optimized by decreasing the zeolite particle size. Creation of a hierarchical zeolite material that possesses both micro- and mesopores with very large surface areas and improved mass transport properties is an effective solution. In this study, a facile approach to a one step synthesis of nanocrystalline ZSM-5 zeolite from a single template system in 12–24 h at 140 °C and with high yield is presented. ZSM-5 zeolite crystals as small as 6 nm which form mesoporous aggregates of approximately 200 nm in diameter were synthesized using this method. The mesopore volume and size distribution showed a dependence on particle size such that smaller particles lead to higher mesopore volumes and narrower pore size distributions. The size of individual crystals, as well as mesopore surface area and pore volume can be controlled by adjusting the pH of the reaction mixture, as well as the hydrothermal treatment temperature and duration.