ZSM-5 Zeolite Crystals Research Articles

Synthesis and Consequence of Aggregated Nanosized ZSM-5 Zeolite Crystals for Methanol to Propylene Reaction

Aggregated nanosized ZSM-5 crystals with a different size from 30–50 nm to 1000–2000 nm were prepared by a hydrothermal synthesis method using a two-step crystallization procedure for methanol to p...

External surface phenomena in dealumination and desilication of large single crystals of ZSM-5 zeolite synthesized from a sustainable source

Abstract Zeolite dealumination and desilication are common methods, which improve accessibility of the active sites located inside the zeolite crystallites and tune the zeolite acidity. The exact mechanism of these post-synthesis zeolite treatments remains under discussion. In this paper, a series of dealuminated and desilicated ZSM-5 zeolites are prepared using single or combined post-synthesis dealumination and desilication of large zeolite single crystals with oxalic acid and sodium hydroxide. The ZSM-5 zeolite has been synthesized using silica extracted from fly ash. Zeolite desilication results in the potholes, leaf-type structures and other clearly visible defects on the surface of zeolite crystallites, while the effect of dealumination is less pronounced. The low temperature nitrogen adsorption suggests the formation of mesopores in the zeolites formed by the voids between and in the irregular zeolite crystallites produced during post-synthesis treatments. 27Al and 29Si MAS NMR in combination with XRD data are indicative of only minor modifications of the bulk zeolite structure during dealumination and desilication. The total Bronsted acidity only slightly decreases and is not affected by the type of zeolite post-synthesis treatment. After desilication of large single crystals of ZSM-5, noticeable enhancement of the Bronsted acidity on the zeolite external surface has been detected by FTIR of adsorbed collidine. The zeolites with higher acidity on the external surface have shown higher activity in the anisole acylation with hexanoic acid. A combination of characterization techniques suggests that the dealumination and desilication of the large crystals of ZSM-5 zeolite using post-synthesis treatments respectively with acid and alkali selectively starts at the zeolite external surface.

Nanoporous ZSM-5 Crystals Coated with Silicalite-1 for Enhanced p-Xylene Separation

The growth of a silicalite-1 coating on ZSM-5 zeolite crystals is one of the surface modification methods allowing to improve its catalytic p-xylene selectivity. Aiming to understand this increase ...

3D Raman Spectroscopy of Large Zeolite ZSM-5 Crystals.

Hydrothermal treatment is a common method used to modify the physicochemical properties of zeolite‐based catalyst materials. It alters the number and type of acid sites through dealumination and increases molecular diffusion by mesopore formation. Steaming also reduces the structural integrity of zeolite frameworks. In this study, Raman microscopy has been used to map large zeolite ZSM‐5 crystals before and after steaming. 3D elemental maps of T−O (T: Al or Si) sites of the zeolite were obtained. The Raman active vibrational bands were determined, which are indicative of (non‐) framework Al, as well as of structural integrity. Zeolite steaming caused the introduction of additional heterogeneities within the zeolite framework. Al migration and the formation of extra‐framework Al species were observed. The described experiments demonstrate the capability of 3D Raman spectroscopy as a valuable tool to obtain information on the spatial distributions of framework elements as well as defects within a zeolite‐based material.

Synthesis of Mesoporous ZSM-5 Zeolite Crystals by a New Organosilane Template with Double-carbamate Carbon Chains

Abstract A new organosilane template with double-carbamate carbon chains were synthesized for preparation of mesoporous zeolites. The structure of the acquired zeolite crystals was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption measurements, and X-ray diffraction (XRD), which indicated that their structure has the same characteristics as ZSM-5 zeolites, and there were about 4 nm and 6 nm mesopores in the acquired zeolites.

Stability of colloidal ZSM-5 catalysts synthesized in fluoride and hydroxide media

Abstract 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.

Kinetic Study of Seed-Assisted Crystallization of ZSM-5 Zeolite in an OSDA-Free System Using a Natural Aluminosilicate as Starting Source

We studied the crystallization of ZSM-5 zeolite by hydrothermal treatment in the absence of organic structure directing agents (OSDA) at 170, 180, and 190 °C, using Perlite as a natural source of S...

Study of the Influence of Aromatization of Propane on Catalytic Systems with Different Dispersion of Crystals of Zeolite ZSM-5

Study of the Influence of Aromatization of Propane on Catalytic Systems with Different Dispersion of Crystals of Zeolite ZSM-5

Graphene Oxide Facilitates Solvent-Free Synthesis of Well-Dispersed, Faceted Zeolite Crystals.

Zeolites with molecular dimension pores are widely used in petrochemical and fine-chemical industries. While traditional solvothermal syntheses suffer from environmental, safety, and efficiency issues, the newly developed solvent-free synthesis is limited by zeolite crystal aggregation. Herein, we report well-dispersed and faceted silicalite ZSM-5 zeolite crystals obtained using a solvent-free synthesis facilitated by graphene oxide (GO). The selective interactions between the GO sheets and different facets, which are confirmed by molecular dynamics simulations, result in oriented growth of the ZSM-5 crystals along the c-axis. More importantly, the incorporation of GO sheets into the ZSM-5 crystals leads to the formation of mesopores. Consequently, the faceted ZSM-5 crystals exhibit hierarchical pore structures. This synthetic method is superior to conventional approaches because of the features of the ZSM-5 zeolite.

Self-assembly of fibrous ZSM-5 zeolites in the presence of sodium alginate

ZSM-5 zeolites with a fibrous morphology were successfully self-assembled in the presence of sodium alginate. The effect of the sodium alginate concentration, Si/Al molar ratio in the synthesis gel, crystallization temperature and time, and the addition order of the sodium alginate on the morphology of the ZSM-5 zeolites was investigated. The possible formation mechanism of fibrous ZSM-5 zeolite crystals was also proposed. The results indicated that the carboxyl and hydroxyl groups of sodium alginate synergistically induced the self-stacking of ZSM-5 nanocrystals and thus the formation of the fibrous ZSM-5 zeolites. The Si/Al molar ratio of the fibrous ZSM-5 zeolites could be adjusted by controlling the amount of the NaAlO2 additive; however, high Si/Al molar ratios also hindered the self-stacking of ZSM-5 nanocrystals. A high crystallization temperature (180°C), a moderate sodium alginate concentration (8.33g/L), and the addition of sodium alginate prior to tetraethoxysilane were necessary for the formation of fibrous ZSM-5 zeolites.

Zeolite-zeolite composite composed of Y zeolite and single-crystal-like ZSM-5 zeolite: Fabricated by a process like “big fish swallowing little one”

Zeolite-zeolite composite composed of Y and ZSM-5 zeolite was prepared using depolymerized Y as partial nutrients for the growth of ZSM-5. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), FT-IR, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), N2 adsorption-desorption measurement and Thermogravimetric analysis (TG). Chemical equilibrium at the solution-crystal interface was changed because of the partially depolymerized Y zeolite, the conditions necessary for the growth of ZSM-5 were therefore obtained. ZSM-5 zeolite crystals nucleated and grew on the interface, and Y zeolite crystals were then gradually swallowed by the growing single-crystal-like ZSM-5.

Engineering of ZSM-5 zeolite crystals for enhanced lifetime in the production of light olefins via 2-methyl-2-butene cracking

ZSM-5 zeolites are tailored for the production of light olefinsvia2-methyl-2-butene cracking.

H-ZSM-5 zeolite model crystals: Structure-diffusion-activity relationship in methanol-to-olefins catalysis

Large ZSM-5 zeolite crystals synthesized in fluoride medium show an astonishing activity, stability as well as selectivity towards light olefins in the Methanol-To-Olefins (MTO) reaction. By proper control of the synthesis parameters, ZSM-5 single crystals of unprecedented high quality are produced. The absence of usually uncontrollable variables such as structural defects, external non selective surface acid sites and extra-framework aluminium (EFAl) species was evidenced by SEM, HRTEM, CO-FTIR, 27Al and 19F MAS-NMR, Rietveld structure refinement and N2- and Ar-gas sorption measurements. Interestingly, diffusivity evaluation of different probe molecules (toluene, benzene and neopentane) has been carried out with PFG-NMR, allowing casting light on an interesting structure-diffusion-activity relationship. A “levitation” effect could be experimentally demonstrated and its impact on catalysis is highlighted in a rationalization attempt: Maxwell-Boltzmann based diffusion models properly predict product distributions for this counter-intuitively outstanding Methanol-To-Propylene (MTP) catalyst.

Synthesis of Mesoporous ZSM-5 Zeolite Crystals by a New Organosilane Template with Double-oxycarbonyl Carbon Chains

Mesoporous zeolites were synthesized by a new organosilane template with double-oxycarbonyl carbon chains. The structure of the zeolite crystals was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption measurements, and X-ray diffraction (XRD), which showed that their structure has the same characteristics as ZSM-5 zeolites, and there were about 4 nm mesopores in the acquired zeolites.

Hollow Alveolus-Like Nanovesicle Assembly with Metal-Encapsulated Hollow Zeolite Nanocrystals.

Inspired by the vesicular structure of alveolus which has a porous nanovesicle structure facilitating the transport of oxygen and carbon dioxide, we designed a hollow nanovesicle assembly with metal-encapsulated hollow zeolite that would enhance diffusion of reactants/products and inhibit sintering and leaching of active metals. This zeolitic nanovesicle has been successfully synthesized by a strategy which involves a one-pot hydrothermal synthesis of hollow assembly of metal-containing solid zeolite crystals without a structural template and a selective desilication-recrystallization accompanied by leaching-hydrolysis to convert the metal-containing solid crystals into metal-encapsulated hollow crystals. We demonstrate the strategy in synthesizing a hollow nanovesicle assembly of Fe2O3-encapsulated hollow crystals of ZSM-5 zeolite. This material possesses a microporous (0.4-0.6 nm) wall of hollow crystals and a mesoporous (5-17 nm) shell of nanovesicle with macropores (about 350 nm) in the core. This hierarchical structure enables excellent Fe2O3 dispersion (3-4 nm) and resistance to sintering even at 800 °C; facilitates the transport of reactant/products; and exhibits superior activity and resistance to leaching in phenol degradation. Hollow nanovesicle assembly of Fe-Pt bimetal-encapsulated hollow ZSM-5 crystals was also prepared.

Self-templating synthesis of hollow spheres of zeolite ZSM-5 from spray-dried aluminosilicate precursor

Synthesis of hollow spheres consisting of ZSM-5 zeolite crystals, prepared by a cost- and time-saving self-templating process, requires neither a hard/soft template for sphere formation nor tetraalkylammonium compound as a zeolite structure-directing agent. A preshaped aluminosilicate precursor, obtained by spray drying of a mixture of colloidal solution of silicic acid and aluminum butoxide, plays the role of a shape-directing agent for the formation of spheres, and is used as a source of silica and alumina for zeolite growth. The zeolite structure is directed using ZSM-5 seeds. This method yielded highly stable hollow spheres with diameters of 15–25 μm, consisting of inter-grown ZSM-5 crystals (Si/Al 14) with a size of 0.5–2.0 μm.

Carbon nanotubes as transient inhibitors in steam-assisted crystallization of hierarchical ZSM-5 zeolites

Carbon nanotubes (CNTs) can be well dispersed in an ethanol diluted zeolite precursor and thus encapsulated in the formed dry gel after solvent evaporation. This specially prepared dry gel allows small quantites of CNTs to effectively act as transient inhibitors in the subsequent steam-assisted crystallization of ZSM-5 nanocrystal aggregates with hierarchical porosity. Although finnally separated from zeolite, CNTs can still transiently inhibit the zeolite growth to avoid fusing into a large crystal. The inter-crystalline mesoporosity in hierarchical ZSM-5 is not created by the space occupied by CNTs, but preserved from the mesoporosity formed by nucleation and initial crystallization. Excessive quantities of CNTs are not recommended because their excessive inhibition induces the appearance of amorphous impurity in hierarchical ZSM-5.

Creation of Mesopores in ZSM-5 Zeolite Crystals by a Novel Double-acyloxy Organosilane Surfactant

Abstract Pores of ca. 11 nm size were created in ZSM-5 zeolite crystals by a novel double-acyloxy amphiphilic organosilane surfactant as a mesopore-directing template. The zeolite crystals had a platelet-like morphology and sponge-like surface. The morphology of the obtained zeolites was compared with conventional zeolite synthesized by the same procedure except for the absence of the double-acyloxy organosilane surfactant.

Differences in the location of guest molecules within zeolite pores as revealed by multilaser excitation confocal fluorescence microscopy: which molecule is where?

A detailed and systematic polarized confocal fluorescence microscopy investigation is presented on three batches of large coffin-shaped ZSM-5 crystals (i.e., parent, steamed at 500 °C, and steamed at 700 °C). In total, six laser lines of different wavelength in the visible region are employed on two crystal positions and three orientations with respect to the polarization plane of the excitation laser light. A fluorescent probe molecule is generated inside the zeolite pores, originating from the acid-catalyzed oligomerization of 4-fluorostyrene. A thorough analysis of the polarization plane of emitting fluorescent light reveals insight into the orientation of the fluorescent probe molecule restricted by the highly ordered zeolite channel framework, thereby visualizing pore accessibility and clearly distinguishing the occupation of straight and sinusoidal channels by the probe molecule. Spectral features are, furthermore, observed to tell apart molecules situated in one or the other pore. Special focus was given on the rim and tip regions of the zeolite ZSM-5 crystals. On the basis of the confocal approach of the investigation, the aforementioned features are evaluated in three dimensions, while the degradation of the zeolite framework upon postsynthesis steam treatment could be visualized by occupation of the sinusoidal pores.

TPAOH Template Removal from High-Silica ZSM-5 by Low-Temperature Hydrocracking

zeolite membranes, especially the mfi-type zeolite membranes, have attracted significant attention for decades because of their special properties. while organic templates such as tetrapropylammonium hydroxide (tpaoh) have typically been used for the synthesis of zsm-5 zeolite and zeolite membranes, the templates remain trapped in the as-synthesized zeolite crystals. a common method for removing organic templates and generating porous frameworks is calcination; however, during this process, the channel structure may be affected. in particular, for zsm-5 membranes, membrane defects may be produced and the separation efficiency therefore may decrease to some extent. in this study, the low-temperature hydrocracking of tpaoh in zsm-5 zeolite crystals was studied under h-2/n-2, while n-2 adsorption, thermogravimetric (tg) analysis, fourier transform infrared (ftir) spectroscopy, temperature-programmed desorption of ammonia (nh3-tpd), and raman spectroscopy were used to characterize zeolite samples. the results show that the organic template in the pores of zsm-5 can be effectively removed below 350 degrees c by low-temperature hydrocracking. characterization analyses by bet specific surface area, tg, ftir, and raman spectroscopy demonstrated that a reducing atmosphere containing h-2 was more conducive to template removal at low temperature than atmospheres of air or n-2. the degree of template removal increased with temperature increasing. the bet surface area of the crystal after hydrocracking at 280 degrees c reached 252 m(2).g(-1), although a small amount of organic residue remained. furthermore, after hydrocracking at 350 degrees c, the bet surface area reached 399 m(2).g(-1), and only trace amount of inorganic carbon residue remained. in addition, the introduction of hydrogen at low temperatures could prevent coke deposits on acid sites and thus zsm-5 zeolite crystals had greater numbers of acidic sites after low-temperature hydrocracking.