Mesoporous ZSM-5 Zeolite Research Articles

Investigation of structure formation mechanism of a mesoporous ZSM-5 zeolite by mesoscopic simulation

Amphiphilic surfactant molecules have a profound influence in directing zeolite crystallization, while the self-assembly process between the functionalized surfactant and aluminosilicate species is the key factor in determining the structure of zeolites. However, such a complex process is extremely difficult to be characterized experimentally. A novel mesoporous ZSM-5 zeolite with hexagonal mesostructures and crystalline microporous frameworks has been synthesized in our previous work. In present research, dissipative particle dynamics (DPD), a mesoscopic simulation method, has been used to investigate the self-assembly process of a surfactant/tetraethylorthosilicate (TEOS)/water system in order to explore the structure formation mechanism of a mesoporous ZSM-5 zeolite. The simulation results show that under a certain composition, the specially designed bifunctional triquaternary ammonium-type surfactant and TEOS can form spherical core–shell micelles. The core (inner section) of a spherical micelle is occupied by hydrophobic beads, while the shell (outer section) is formed by hydrophilic beads. Besides, an ordered, uniform mesophase can be formed under a constant shear rate and transformed into mesoscale structure. The simulation results are consistent with the corresponding experimental results. Overall, the DPD simulation is a valuable tool to investigate the porogenic mechanism of surfactants. The present approach may open a window for investigating the formation mechanism of mesoporous zeolites that involves the surfactant-driven synthesis process.

Postsynthesis of mesoporous ZSM-5 zeolite by piperidine-assisted desilication and its superior catalytic properties in hydrocarbon cracking

Mesoporous ZSM-5 zeolites with unique hydrocarbon cracking properties have been postsynthesized from conventional ZSM-5 samples using small molecular organic amine-assisted desilication technique.

A facile strategy for enhancing FeCu bimetallic promotion for catalytic phenol oxidation

The mesoporous ZSM-5 zeolite obtained from alkaline treatment was found to be a superior support of bimetallic FeCu, minimizing the nanoparticle size, enhancing the bimetallic interaction, and promoting catalytic oxidation of phenol.

Synthesis of Mesoporous Zeolite ZSM-5 via Gel Conversion with Polyethyleneglycol as Template and Its Catalytic Performance

Synthesis of Mesoporous Zeolite ZSM-5 via Gel Conversion with Polyethyleneglycol as Template and Its Catalytic Performance

Desilication of ZSM-5 zeolites for mesoporosity development using microwave irradiation

Highlights: • Microwaves have beneficial effects on desilication of zeolites. • Produced mesopores with microwaves have narrow pore-size distribution. • Advantages and disadvantages of various desilicating agents were also reported. - Abstract: Mesoporous ZSM-5 zeolite was obtained by desilication in alkaline solutions with microwave (MW) and conventional electric (CE) heating under hydrothermal conditions. Both methods were effective in the production of mesoporous zeolites; however, MW was more efficient than CE as it led to well-defined mesopores with relatively small sizes and a narrow size distribution within a short treatment time. Moreover, the mesoporous ZSM-5 obtained through this method was effective in producing less bulky products from an acid-catalyzed reaction, specifically the butylation of phenol. Finally, various bases were found to have advantages and disadvantages in desilication. NaOH was the most reactive; however, macroporosity could develop easily under a severe condition. Ammonia water was weakly reactive; however, it could be used to precisely control the pore architecture, and no ion exchange is needed for acid catalysis. Organic amines such as ethylenediamine can also be used in desilication.

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.

Investigation on the morphology of hierarchical mesoporous ZSM-5 zeolite prepared by the CO2-in-water microemulsion method

A series of hierarchical mesoporous ZSM-5 zeolites with different morphology were successfully synthesized by the CO2-in-water microemulsion method, and mesoporosity was formed without organotemplate. The different synthesis conditions, including silica alumina molar ratio, stirring time and compressed CO2 pressure, were systematically investigated to discuss the influence of these conditions on the morphology of ZSM-5 zeolite. The resulting samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP) and nitrogen adsorption-desorption measurement. XRD results indicated that compressed CO2 route for the synthesis of MFI zeolites had a fast crystallization rate and good crystallinity. SEM images showed that the ZSM-5 hierarchical mesoporous ZSM-5 zeolite had a uniform chain-like crystal morphology, whereas silicalite-1 displayed a monodisperse crystal morphology. In addition, the nitrogen adsorption-desorption measurement provided sufficient evidence for the presence of hierarchical mesopores in ZSM-5 zeolite.

Benzylation of Naphthalene over a Mesoporous ZSM-5 Zeolite Microsphere Catalyst

Benzylation of Naphthalene over a Mesoporous ZSM-5 Zeolite Microsphere Catalyst

Catalytic fast pyrolysis of biomass with mesoporous ZSM-5 zeolites prepared by desilication with NaOH solutions

This study investigated the effects of desilication of ZSM-5 zeolite on its catalytic properties in catalytic fast pyrolysis (CFP) of lignocellulosic biomass. A series of mesoporous ZSM-5 zeolites were prepared by desilication of a conventional microporous ZSM-5 zeolite with NaOH solutions of varying concentrations (0.1–0.5M). The creation of mesopores improved the diffusion property of the desilicated ZSM-5 zeolites and their catalytic activity for cracking bulky oxygenates (e.g., syringols derived from the lignin component of biomass). Consequently, the desilicated zeolites produced more aromatic hydrocarbons (carbon yields of 26.2–30.2%) and less coke (39.9–41.2%) in CFP of beech wood than the parent microporous ZSM-5 (23.2% aromatics and 44.4% coke). The highest aromatic yield (30.2%) and lowest coke yield (39.9%) were obtained in CFP of beech wood with mildly desilicated zeolite treated with 0.3M NaOH solution. However, desilication with a greater concentration, 0.5M NaOH, decreased the aromatic yield to 26.2% due to a considerable loss of microporosity in the severely desilicated zeolite. The results indicate that carefully controlled desilication of zeolite can improve the conversion of lignocellulose to valuable aromatic hydrocarbons and decrease the formation of undesired coke, thus improving the product distribution in CFP of lignocellulose.

Hierarchical mesoporous ZSM-5 for the dehydration of methanol to dimethyl ether

Hierarchical mesoporous ZSM-5 zeolites were synthesized using small organic cations of tetrapropylammonium and meso-sized cationic polymers of dimethyldiallyl ammonium chloride acrylamide copolymer as templates. The zeolites were used for the dehydration of methanol to dimethyl ether (DME). Characterization results showed that the basic MFI-type structure was still obtained after adding the cationic polymers, while their nitrogen isotherms exhibited a broad hysteresis loop at relative pressures higher than 0.4, which proved the presence of mesopores. The mesoporosity of the hierarchical mesoporous ZSM-5 can be adjusted simply by adding different amounts of the cationic polymer. Catalytic tests showed that the hierarchical mesoporous HZSM-5 zeolites exhibited better stability than conventional HZSM-5 and excellent DME selectivity. The activity for methanol dehydration strongly depended on the textural property and acidity of the catalyst. The synthesized hierarchical mesoporous HZSM-5 zeolites exhibited better catalytic activity than conventional HZSM-5, indicating that hierarchical mesopores play an important role in the methanol to dimethyl ether process.

Hierarchical mesoporous ZSM-5 zeolite with increased external surface acid sites and high catalytic performance in o-xylene isomerization

Surface acid sites of hierarchical mesoporous ZSM-5 zeolite synthesized by steam-assisted crystallization were characterized by NH3 temperature-programmed desorption and in-situ infrared spectroscopy. Compared with the conventional ZSM-5 zeolite, the hierarchical ZSM-5 zeolite had a lower concentration of surface acid sites. However, the hierarchical structure had more Lewis acid sites and, more importantly, much more external active sites as confirmed by 2,6-di-tert-butylpyridine infrared spectroscopy. Such hierarchical structure exposed more acid sites on the external surface, which subsequently lead to higher catalytic activity in reactions involving bulky molecules, such as o-xylene isomerization.

Synthesis, characterization and catalytic activity of a novel mesoporous ZSM-5 zeolite

A novel mesoporous ZSM-5 zeolite was hydrothermally synthesized using glucose as a template. Characterizations by XRD, TEM and nitrogen isotherms indicated that ZSM-5 possessed worm-like mesoporous. 27Al-MAS-NMR and NH3-TPD showed that the mesoporous ZSM-5 preserved tetrahedral coordination aluminum and stronger acidity than conventional mesoporous material. As-prepared mesoporous ZSM-5 was successfully used in alkylation reaction of phenol with tert-butanol and exhibited significantly high phenol conversion and 2,4-DTBP selectivity. In addition, the hydrothermal stability was also studied by boiling in water for 7 days and displayed good results.

Ionic liquid confined zeolite system: an approach towards water mediated room temperature synthesis of spiro[pyrazolo[3,4-e]benzothiazepines

A novel ionic liquid confined ZSM-5 zeolite catalyst system has been developed using different ionic liquids confined within a mesoporous ZSM-5 zeolite; their catalytic activity has been tested in aqueous media at room temperature for the greener synthesis of spiro[pyrazolo[3,4-e]benzothiazepine] analogues in higher yield with shorter reaction time for the first time. Recyclability of the novel catalyst system was also studied which resulted in no loss of their catalytic activity in up to five cycles making the whole system industrially viable.

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.

Surface and Pore Structure Assessment of Hierarchical MFI Zeolites by Advanced Water and Argon Sorption Studies

Advanced physicochemical characterization of the pore structure of hierarchical zeolites, including the precise knowledge of pore size, interconnectivity, and surface properties, is crucial in order to interpret their superior performance in catalytic and adsorption applications. Postsynthetic mesopore formation by alkaline treatment of zeolites leads to simultaneous compositional changes due to the selective dissolution of silicon. By careful tuning of these effects through subsequent acid treatment, the Si/Al ratio can be restored to that of the parent zeolite. We evaluate the application of argon (87.3 K) and water (298.5 K) adsorption to assess the porous properties of mesoporous ZSM-5 zeolites with equivalent porosity, but differing composition. An accurate and combined micro/mesopore size analysis is obtained by applying NLDFT (nonlocal density functional theory) analysis on the argon isotherms. The argon adsorption data clearly reveal the two different relative pressure regions of micro- and mesopo...

Direct synthesis of mesoporous ZSM-5 zeolite by a dual-functional surfactant approach

Mesoporous molecular sieves with crystalline microporous walls of ZSM-5-like frameworks was directly prepared by a dual-functional triquaternary ammonium-type surfactant. Mesopores are generated by surfactant aggregates and crystalline microporous zeolite frameworks within the mesopore walls are directed by quaternary ammonium functional groups of surfactant. The mesoporous zeolite sample was characterized by a complementary combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption isotherms, Fourier transform infrared spectroscopy, 27Al MAS NMR spectra and density functional theory calculation. The results suggest that present method is suitable as a direct synthesis route to highly mesoporous zeolites. Due to the short diffusion routes and strong acidity, the mesoporous ZSM-5 zeolite displayed a clear advantage on catalysis reactions involving large molecules compared to commercial zeolites and mesoporous amorphous materials. The present approach provides an efficient route to synthesize other related mesoporous zeolites in the future.

Assembly of a hierarchical zeolite-silica composite by spray drying

We report a one-step spray drying synthesis of a multimodal composite based on a polymer-templated silica matrix enclosing a mesoporous ZSM-5 zeolite. The first level of porosity, comprising the silica matrix with 13–25 nm mesopores, is generated by evaporation-induced assembly of the silica nanoparticles together with the non-ionic surfactant using spray drying. The mesoporous zeolite contributes with micropores (0.56 mm) and intracrystalline mesopores (∼7 nm) introduced by controlled alkaline leaching. The nanostructured composite, featuring agglomerated zeolite microgranules uniformly covered by the silica, displayed tuneable properties of the matrix mesoporosity and particle size by changing both the silica source and the spray drying conditions. The structural and acidic properties of the zeolite phase were not altered by the assembly method. The technique was successfully applied to other zeolite structures (USY, mordenite and ferrierite) with no impact in the characteristics of the matrix. This fast, versatile, reproducible, economical and scalable technique represents a powerful strategy for creating hierarchically structured materials with adjustable micro-, meso- and macroporous properties and enhanced agglomeration.

A facile route to synthesize mesoporous ZSM-5 zeolite incorporating high ZnO loading in mesopores

Mesoporous ZSM-5 zeolite incorporating ZnO in mesopores has been synthesized with a simple route. The commercial H-ZSM-5 (Si/Al=50) was first treated with NaOH solution to induce a partial desilication, which can introduce a large number of intracrystal mesopores, and the ZnO nanoparticles were successfully incorporated in the mesopores with wet impregnation method. Characterizations of XRD, UV–visible absorption spectra, TEM and N2 adsorption were taken to analyze the locations of ZnO nanoparticles. The mesopores can load more than 15% ZnO with the size of about 20nm, which can only reduce the mesopore surface area and volume, whereas, micropores are remained and cannot be blocked by the loaded ZnO particles.

Hierarchical Mesoporous Zeolites: Direct Self‐Assembly Synthesis in a Conventional Surfactant Solution by Kinetic Control over the Zeolite Seed Formation

By kinetic control over the zeolite seed formation, we report the direct fabrication of hierarchical mesoporous zeolites using hexadecyl trimethyl ammonium bromide (CTAB) as the soft template in a conventional solution route. Nanometer-sized, subnanocrystal-type zeolite seeds with a high degree of polymerization are essential to prevent the formation of a separate amorphous mesoporous phase and the phase separation between the mesophase and zeolite crystals in the presence of CTAB and a certain amount of ethanol. The mechanisms for the formation of hierarchically porous zeolites in the solution process, including the effect of mother liquid aging, formation of subnanocrystal zeolite seeds and their self-assembly effect with CTAB, and the role of ethanol are proposed and discussed in detail. The prepared mesoporous ZSM-5 zeolite showed much higher catalytic activity than conventional counterparts for aldol condensations involving large molecules, especially in the synthesis of vesidryl.