ZSM-5 Aggregates Research Articles

Synthesis of ZSM-5 aggregates made of zeolite nanocrystals through a simple solvent-free method

In the traditional hydrothermal synthesis of zeolites, the solvent of water is necessary for crystallization, so large amount of wastewater containing NaOH and organic pollutants could be inevitably produced. The solvent-free route is considered to remarkably enhance the synthesis efficiency and reduce the energy and pollutants in large scale production of zeolites, but the zeolites obtained usually consist of micrometer sized single crystals which only possess micropores and long diffusion pathway for molecules. In this study, a novel solvent-free synthesis system made of solid raw materials of anhydrous silica and aluminum sources, organic template and Na2CO3·10H2O, was demonstrated to synthesize ZSM-5 zeolite particles composed of nanocrystals of about 10–40 nm in size. The obtained ZSM-5 particles possess high crystallinity and surface area, and well-developed mesoporosity (5.2 nm) and excellent catalytic activity in polymer cracking, such as low-density polyethylene (LDPE), which is the main source of white pollution. The ZSM-5 aggregate particles with the micro-/meso- porous structure have the potential used as catalysts and adsorbents in industry.

Synthesis of ZSM-5 with hierarchical porosity: In-situ conversion of the mesoporous silica-alumina species to hierarchical zeolite

Hierarchical ZSM-5 aggregates were fabricated using the conventional surfactant cetyltrimethylammonium bromide (CTABr) as the mesoporogen together with 1, 6-diaminohexane (HDA) as structure-directing agent. The competition of the templates and the subsequent phase separation were effectively avoided. A possible formation mechanism was proposed based on the investigation of the crystallization process. The obtained hierarchical ZSM-5 aggregates were highly crystallized, possessing large external surface area, mesopore volume and regular mesopore size distributions. And they were proved to be more efficient in catalytic LDPE cracking due to improved accessibility of large polymer molecules to the active sites. This method was facile and cost-effective, applicable within a wide SiO2/Al2O3 ratio by using various silica sources.

Direct synthesis of monolithic nano-sized ZSM-5 aggregates possessing ordered mesoporosity by controlling arrangement of nanoparticles

This work presents a facile method for synthesizing monolithic ZSM-5 nanoparticle aggregates (ZNA) by directly converting the ordered mesoporous material Al-SBA-15 under low solvent content conditions. The effects of crystallization temperature, time, and the structure-directing agents (SDAs) content on the textural properties and on the crystallinity of the final product were investigated. The crystal growth was physically confined to a nano-scale space surrounded by chemically inert units previously formed through the controllable decomposition of P123 micelles. The resulting nanoparticles exhibit uniform size in the range of 20–40 nm. Moreover, ZNA has a monolithic morphology of several micrometers in size, closely resembling that of raw Al-SBA-15, allowing the avoidance of a high-speed centrifugal separation process. The location of nanoparticles inside ZNA bulk particles can be mainly restricted to replicating the Al-SBA-15 walls by slowing down the inorganic species consumption process, and consequently, forming a visibly ordered mesostructure.

In-situ conversion of Al-SBA-15 wall structures to monolithic ZSM-5 nanoparticle aggregates

The amorphous wall structure of Al-SBA-15 was converted in-situ to uniform ZMS-5 nanocrystal aggregates. Si/Al ratio in resulting ZSM-5 nanocrystal aggregates is close to that of raw Al-SBA-15. The ZSM-5 aggregates exhibits a monolithic morphology, a replica of the shape of raw Al-SBA-15, which significantly allows the avoidance of a high-speed centrifugal separation process. The incompletely decomposed structure-directing template of Al-SBA-15 works as inert units inserting in the mesopores of Al-SBA-15 materials. The nucleation and growth of zeolite were physically confined inside a nano-scale space surrounded by the chemically inert units that were generated from the controlled decomposition of the surfactant.

Synthesis of ZSM-5 aggregates by a seed-induced method and catalytic performance in methanol-to-gasoline conversion

A seed-induced method was applied to synthesize a series of ZSM-5 aggregates using silicalite-1 (S-1) as seeds. The samples were characterized by several techniques and studied in the methanol-to-gasoline (MTG) conversion reaction in a continuous fixed-bed reactor. The results showed that the molar ratios of Na 2 O/SiO 2 and H 2 O/SiO 2 in the precursors had great effects on the physicochemical and catalytic properties. The ZSM-5 aggregates with the highest crystallinity, external surface areas, micropore volumes, mesopore volumes and small primary crystal and aggregate sizes, obtained with the molar composition of 0.12Na 2 O–1SiO 2 –0.02Al 2 O 3 –25H 2 O-0.01Seed in the precursor, exhibited the highest stability.

Direct synthesis of high-silica nano ZSM-5 aggregates with controllable mesoporosity and enhanced catalytic properties

In the absence of additional mesoporous template, high-silica nano-sized ZSM-5 aggregates have been rapidly synthesized by solid-like state conversion.

Aerosol-assisted synthesis of nano-sized ZSM-5 aggregates

An aerosol-assisted method is used to synthesize nano-sized ZSM-5 aggregates with good texture properties and Al species distribution.

Direct synthesis of self-assembled ZSM-5 microsphere with controllable mesoporosity and its enhanced LDPE cracking properties

Diffusion-enhanced ZSM-5 aggregates by n-hexylamine directing are obtained with easy control on mesopore and the possible growth mechanism is proposed.

High-resolution single-molecule fluorescence imaging of zeolite aggregates within real-life fluid catalytic cracking particles.

Fluid catalytic cracking (FCC) is a major process in oil refineries to produce gasoline and base chemicals from crude oil fractions. The spatial distribution and acidity of zeolite aggregates embedded within the 50–150 μm-sized FCC spheres heavily influence their catalytic performance. Single-molecule fluorescence-based imaging methods, namely nanometer accuracy by stochastic chemical reactions (NASCA) and super-resolution optical fluctuation imaging (SOFI) were used to study the catalytic activity of sub-micrometer zeolite ZSM-5 domains within real-life FCC catalyst particles. The formation of fluorescent product molecules taking place at Brønsted acid sites was monitored with single turnover sensitivity and high spatiotemporal resolution, providing detailed insight in dispersion and catalytic activity of zeolite ZSM-5 aggregates. The results point towards substantial differences in turnover frequencies between the zeolite aggregates, revealing significant intraparticle heterogeneities in Brønsted reactivity.

Dispersion and Orientation of Zeolite ZSM‐5 Crystallites within a Fluid Catalytic Cracking Catalyst Particle

Confocal fluorescence microscopy was employed to selectively visualize the dispersion and orientation of zeolite ZSM-5 domains inside a single industrially applied fluid catalytic cracking (FCC) catalyst particle. Large ZSM-5 crystals served as a model system together with the acid-catalyzed fluorostyrene oligomerization reaction to study the interaction of plane-polarized light with these anisotropic zeolite crystals. The distinction between zeolite and binder material, such as alumina, silica, and clay, within an individual FCC particle was achieved by utilizing the anisotropic nature of emitted fluorescence light arising from the entrapped fluorostyrene-derived carbocations inside the zeolite channels. This characterization approach provides a non-invasive way for post-synthesis characterization of an individual FCC catalyst particle in which the size, distribution, orientation, and amount of zeolite ZSM-5 aggregates can be determined. It was found that the amount of detected fluorescence light originating from the stained ZSM-5 aggregates corresponds to about 15 wt %. Furthermore, a statistical analysis of the emitted fluorescence light indicated that a large number of the ZSM-5 domains appeared in small sizes of about 0.015-0.25 μm(2), representing single zeolite crystallites or small aggregates thereof. This observation illustrated a fairly high degree of zeolite dispersion within the FCC binder material. However, the highest amount of crystalline material was aggregated into larger domains (ca. 1-5 μm(2)) with more or less similarly oriented zeolite crystallites. It is clear that this visualization approach may serve as a post-synthesis quality control on the dispersion of zeolite ZSM-5 crystallites within FCC particles.

A fast route for synthesizing nano-sized ZSM-5 aggregates

Nano-sized ZSM-5 aggregates have been rapidly synthesized from leached metakaolin by solid-like state conversion. Compared with the conventional hydrothermal route, the nano-sized ZSM-5 aggregates obtained by this method showed more excellent catalytic performance, C2–C4 olefin selectivity and longer lifetime to endure coke deposition.

Spatial Distribution of Zeolite ZSM‐5 within Catalyst Bodies Affects Selectivity and Stability of Methanol‐to‐Hydrocarbons Conversion

Implicated in the catalysis crime: The spatial distribution of zeolite ZSM-5 aggregates within industrial-like catalyst bodies has a vast impact on the methanol-to-olefin selectivity and overall stability of the catalyst. Catalyst bodies with smaller ZSM-5 aggregates yield more olefins, less paraffins, and significantly less coke than catalyst bodies containing less dispersed ZSM-5 crystals. This result has direct implications on the way catalysts are prepared and manufactured.

Seed-induced synthesis of mesoporous ZSM-5 aggregates using tetrapropylammonium hydroxide as single template

Mesoporous ZSM-5 aggregates were synthesized with wide SiO2/Al2O3 ratio range using tetrapropylammonium hydroxide as single template through seed-induced route. The influences of SiO2/Al2O3 ratio, Na2O/SiO2 ratio and seeding gel amount on the textural properties of the mesoporous ZSM-5 aggregates were investigated and the possible formation mechanism was brought forward. The mesoporous ZSM-5 aggregates of approximately 2.0μm in diameter were formed by nanosized crystals several tens nanometers in size, which avoid the filtration difficulties for nanosized crystals. This synthesis process is facile and much less expensive while the prepared mesoporous ZSM-5 aggregates possess large external surface area and large mesopore volume.

One-step synthesis of hierarchical aluminosilicate aggregates using bifunctional alkanolamine as single template

Highly active, hierarchical zeolite ZSM-5 aggregates have been prepared in a one-step synthesis using alkanolamine as single template. The effects of SiO 2/Al 2O 3, pH and H 2O/SiO 2 on the aggregate morphology of the ZSM-5 nanocrystals were investigated. The obtained aggregate zeolites characterized by SEM, TEM and BET possessed significant textual porosity (up to 0.22 cm 3/g), which could be tuned by the number of substituents in the alkanolamine molecules and the amount of aluminum in the synthetic mixtures. These zeolite aggregates showed high activities for Friedel–Crafts alkylations and may curtail the filtration difficulties during the synthesis and applications to some extent.

In situ assembly of ZSM-5 nanocrystals into micro-sized single-crystal-like aggregates via acid-catalyzed hydrolysis of tetraethylorthosilicate

ZSM-5 aggregates were synthesized with the silica source tetraethylorthosilicate (TEOS) being hydrolyzed at acidic conditions to produce siliceous precursors, followed by the addition of aluminum sulfate and tetrapropyl ammonium bromide (TPABr), and with the resulting gel mixture being hydrothermally crystallized at basic conditions. The obtained products were characterized by XRD, SEM, and N2 adsorption. Well crystallized ZSM-5 can be successfully synthesized through the sulfuric acid-catalyzed hydrolysis of TEOS within a short crystallization time 35 h. The thus produced micro-sized single-crystal-like zeolite ZSM-5 aggregates (10 μm) are made of uniformly distributed nanocrystals with sizes of about 200 nm. Moreover, by adjusting the hydrothermal reaction parameters, such as increasing the crystallization temperature, the TPABr/SiO2 ratio and the pH value of reaction solution, the crystallization is accelerated substantially. Also, the moderate H2O/SiO2 molar ratio of 20–60 in the synthesis mixture can lead to pure ZSM-5, and yet the optimal ratio is 40.

Catalytic properties of nano-sized ZSM-5 aggregates

Nano-ZSM-5 (NZ) with well-defined porosity was synthesized by organic silica method. The material exhibited more than a twofold increase in pore volume when compared to the normal ZSM-5 (HZ). The increase in pore volume is observed in the entire range of the pores with diameter from 5 Å to 1500 Å. The order of increase in volume is macropores (>500 Å) > micropores (up to 20 Å) > mesopores (20–500 Å). Although macropore and mesopore formation is responsible for the major increase in the pore volume, significant increase in zeolitic pore volume was also observed in NZ. Both the ZSM-5 materials were tested for esterification of cyclohexanol with acetic acid under autogeneous pressure conditions where NZ showed better activity (69% conversion).

Low temperature synthesis and properties of ZSM-5 aggregates formed by ultra-small nanocrystals

ZSM-5 formed by aggregates of nanocrystals with ultra-small crystal size (10–20 nm) has been prepared by hydrothermal crystallization of clear synthesis mixtures at low temperatures (70–90 °C) under atmospheric pressure. Compared with the conventional autoclave treatment, this method leads to a significant reduction in the crystal size, although with lower zeolite yields, which has been assigned to the mild conditions used (low temperature and atmospheric pressure), as they may prevent the crystal growth by aggregation/densification of primary units in the nanometer range. Characterization of the samples obtained at long synthesis times by both X-ray and electron diffraction show they are highly crystalline materials, indicating that the ultra-small crystal size is compatible with the detection of crystallinity. After calcination, most of the Al atoms remain tetrahedrally coordinated, which is a proof of their stability. The nanosized ZSM-5 exhibits a very high external surface area (typically around 200 m 2/g), as a consequence of its small crystallites, making this material a potentially interesting catalyst for the conversion of bulky molecules. Likewise, a mathematical model has been developed which correlates the variation of the textural properties of the ZSM-5 zeolite with its crystal size.