ZSM-5 Zeolite Crystals Research Articles

Nonionic polymer and amino acid-assisted synthesis of ZSM-5 nanocrystals and their catalytic application in the alkylation of 2-methylnaphthalene.

The synthesis of nanosized ZSM-5 zeolites with high crystallinity and suitable acidity is very significant for their great potential in various catalytic applications. Herein, a series of zeolite ZSM-5 crystals with different particle sizes and SiO2/Al2O3 ratios (10-30) were synthesized by a temperature-varying two-step crystallization method in a concentrated gel system containing L-lysine and/or polyvinylpyrrolidone (PVP) additives. By optimizing the addition amounts of the two additives, the crystal size of the ZSM-5 zeolite could be reduced to less than 100 nm. Meanwhile, relatively high crystallinity and framework Al incorporation rates could be achieved, resulting in the generation of high-quality ZSM-5 nanocrystals. The nanosized H-form ZSM-5 zeolite with a SiO2/Al2O3 ratio of 20 showed enhanced catalytic efficiency and stability for the alkylation of 2-methylnaphthalene (2-MN) with methanol to produce an important intermediate, 2,6-dimethylnaphthalene (2,6-DMN). A relatively high and steady yield of 2,6-DMN (above 7.2%) could be achieved during 20 h time-on-stream at 400 °C. The smaller crystal size, higher crystallinity and framework Al content could provide more accessible Brønsted acid sites in the 10-membered ring channel of the ZSM-5 nanocrystals, which are the main active sites responsible for the shape-selectivity of the targeted product of 2,6-DMN. As a result, the formation of other side products like 1-MN and poly-MN could be effectively inhibited, thus leading to an improved 2,6-DMN yield and coke resistance over the nanosized ZSM-5 catalyst.

Preparation and characterization of ZSM-5 zeolite

Recently, zeolites attracted considerable research attention because they exhibit adsorption properties, ion exchange capabilities and a good catalytic property, a specific pore size distribution; a unique chemical and thermal properties and several applications. 
 Actually zeolites play a crucial role as a catalyst to capture and convert Carbone dioxide into valuable products.
 In the present work, hydrothermal synthesis of ZSM-5 zeolite crystals, with composition of the chemical products 0.01 Al2O3,1SiO2,2 NaOH, 0.15 TPABr, 18.34 H2O at 170°C for 48 hours (2 days) at Ph 11 is described. 
 Results of characterization of the ZSM-5 zeolite by XRD, FTIR, EDAX, SEM, TGA, are presented and discussed.

Modulating hierarchical ZSM-5 crystals from etching-assisted growth with substituted phenols

The rational modulation of zeolite microstructures tailoring crystal morphology and hierarchy, is an effective way to promote their mass transport and catalytic performance. However, practical realization remains challenging. We recently demonstrated a novel etching-assisted crystallization process that allows fine control over zeolite architecture by eliminating intermediate defective nanocrystals with active proton-bearing organic molecules such as phenol. Here, we investigated in detail the phenolic etching effect on the crystallization of ZSM-5 zeolites using a combination of techniques including diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) and 2D 27Al multiple quantum magic angle spinning nuclear magnetic resonance (MQ MAS NMR) and systematically elucidated the structure modulation with a homologous series of phenolic compounds. Time-series characterizations confirmed the initial seed formation, intermediate dissolution, and final perfected crystallization stages during ZSM-5 synthesis in the presence of phenolic compounds. Since deprotonation to phenolate anion in-situ is required during alkaline zeolite synthesis, the electron-withdrawing (EW) groups on the phenol para-position lead to bigger ZSM-5 crystals with more mesopores, while the phenolic molecules with para- electron-donating (ED) groups exhibit less significant effect. Under the same initial pH, the phenolic compounds show unparalleled compatibility with zeolite crystallization by stabilizing the system pH values, whereas inorganic acids invariably fail the zeolite crystallization. Given the remarkable kinetic control over zeolite growth through the simultaneous but opposite nucleophilic etching process, our observation provides a versatile way to manipulate zeolite crystallization with high tunability.

Synthesis of b-axis oriented ZSM-5 zeolite by mechanochemical-assisted quasi-solvent-free method and its MTO catalytic performance

In this paper, b-axis oriented ZSM-5 zeolite was synthesized by solvent-free method with ammonia as growth regulator. Zeolites were characterized by modern detection techniques such as XRD, SEM, BET and NH3-TPD. The results showed that ammonia could not only promote the crystallization of ZSM-5 zeolite, but also direct the synthesis of ZSM-5 zeolite with b-axis oriented morphology, which was beneficial to enhance the selectivity of light olefins. B-axis oriented ZSM-5 zeolite did not need to be mixed and aged in aqueous solution, which could reduce the discharge of sewage, and avoided the generation of autogenic pressure in the crystallization process. Furthermore, it is consistent with the concept of environmental friendliness, which could guide the green preparation of industrial ZSM-5 zeolites.

Synthesis of thin ZSM-5 zeolite membranes in a self-terminating mother liquor

Low-cost synthesis of thin zeolite membranes is extremely desirable, yet challenging. In this study, we realized template-free synthesis of ultrathin ZSM-5 membranes by conventional hydrothermal synthesis on regular ceramic support. The key is to choose a self-terminating mother liquor with high Si/Al ratio. The crystallization process (formation of ZSM-5 zeolite crystals and membrane) in this Al-deficient mother liquor is an Al-driven process. The crystallization led to fast depletion of Al in the mother liquor which triggered the termination of crystallization process in this template-free mother liquor. Therefore, the thickness of ZSM-5 membrane can be controlled easily by adjusting the ratio of mother liquor/membrane area, which is much simpler than membrane synthesis in conventional mother liquor. The obtained ultrathin MFI membranes exhibited outstanding separation performance for butane isomers. This strategy can also be applied to the synthesis of other types high-silica zeolite membranes.

Effect of zeolite structure and addition of steam on naphtha catalytic cracking to improve olefin production

In this study, steam catalytic cracking of dodecane (a model representative of naphtha) was investigated both with and without steam. The reaction utilized the different 3D sinusoidal microporous channels in submicron ZSM-5 and BEA zeolite crystals to convert dodecane to light olefins. Although both synthesized submicron catalysts (400–500 nm) have similar Brønsted/Lewis acid ratios, the BEA zeolite exhibited higher surface acidity than ZSM-5 zeolite. In addition, the steam addition has significantly affected the zeolites structure, even though their cracking activity was not affected. However, the zeolites structural modification has shown significant effect on the pore shape selectivity which result in different light olefins yields. During catalytic cracking in the absence of steam, hydrogen transfer reaction was less favored over BEA zeolite, which result in higher light olefins selectivity and dry gas formation than with ZSM-5 zeolite. In the presence of steam, ZSM-5 pore-shape modification favored the monomolecular cracking pathway leading to achieving higher light olefin yield than that observed over BEA zeolite. The study demonstrated that ethylene/propylene ratio (E/P) is impacted by zeolite structure which is affected by the steam addition during the reaction.

Highly dispersed Pd nanoparticles confined in ZSM-5 zeolite crystals for selective hydrogenation of cinnamaldehyde

Selective hydrogenation of α,β-unsaturated aldehyde catalyzed by supported Pd nanoparticles (NPs) is challenging, especially under harsh reaction conditions. Here, we report a facile method to prepare a catalyst composed of highly dispersed Pd NPs (∼2.6 nm) confined in zeolite ZSM-5 crystals. When used in the hydrogenation of cinnamaldehyde, the prepared catalyst ([email protected]) exhibited excellent performance for the selective production of hydrocinnamaldehyde (HCAL) due to the confinement effect. Compared with the traditional supported Pd catalyst prepared by impregnation, [email protected] showed a 2.5-fold enhancement in the HCAL selectivity (73% vs. 30%). Liquid adsorption combined with infrared spectroscopy characterization revealed that compared with the traditional catalyst, [email protected] adsorbed much less reactant as well as product molecules and desorbed the generated HCAL quickly, thereby suppressing the formation of by-products and leading to high selectivity of HCAL.

Encapsulation of ultra-small Cu–Fe into ZSM-5 zeolites for NH3-SCR with broad reaction-temperature ranges

A direct hydrothermal synthesis strategy is developed to prepare the Cu–Fe-ZSM-5 zeolites by using the ethylenediaminetetraacetic acid disodium dihydrate (EDTA-2Na·2H2O) chelated Cu2+ and Fe3+ precursors as metal sources. During the crystallization, the metal chelates were spontaneously embedded into the ZSM-5 crystals and subsequently transformed to the zeolites encapsulated copper and iron species after removing the chelating agent via the high-temperature calcination. Rigorous characterizations indicate that the resulted Cu2+/Cu+ and Fe3+/Fe2+ species are formed ultra-small nano-composites with an average diameter of ∼2.2 nm and highly dispersed in the ZSM-5 zeolite crystals. The acidity of the ZSM-5 zeolites is subtly modulated by the encapsulated Cu–Fe nano-composite. As expected, the as-prepared Cu–Fe-ZSM-5 exhibits outstanding catalytic performance for the selective catalytic reduction of NOx with ammonia (NH3-SCR) in the broad reaction temperature ranges of 220–480 °C, which is much better than the Cu–Fe/ZSM-5 prepared with the conventional wetness impregnation method. Furthermore, the resultant zeolites show high stability and good tolerance to H2O and SO2, and it is very competitive for practical application to eliminate NOx. The developed one-pot hydrothermal synthesis route by using EDTA-2Na·2H2O as chelating agent is very convenient and easily reproducible, providing a general guideline to design and fabricate the superior transition metal modified zeolite catalysts for NH3-SCR and the related reactions.

ZSM-5 zeolite coatings on perlite support for MTO application

ZSM-5 zeolite crystals were grown via an in situ hydrothermal synthesis on perlite supports. In this study, cheap perlite mineral, which mainly contains SiO2 and metal oxides (Al2O3, CaO, MgO), was used as aluminum source and support material for binderless zeolite crystals growth. Hence, this synthesis strategy neither needs the introduction of Al, nor support surface functionalization steps, which may diminish the cost. Besides, the highly porous structure and the big particle size of ZSM-5/perlite composites are beneficial to reduce the pressure drop along the catalyst bed, rendering easier the heat and mass transfer of the products. In addition, the influence of different particle sizes (4–3, 3–1.5 and 1.5–0.5 mm) and quantities (1–3 g) of ZSM-5/perlite without any further modification were successfully evaluated in the Methanol-To-Olefins reaction (MTO). An optimized ZSM-5/perlite structured catalyst exhibited a high stability at full methanol conversion during 14 h on stream, along with a 80% selectivity towards light olefins at 475 °C. In addition, this catalyst still exhibited an excellent catalytic activity at relatively low temperature (350 °C), the methanol conversion remaining 96% after 28 h on stream. Finally, the conversion was maintained at 95% during 8 h on stream at WHSV = 8 h−1 with a propylene selectivity of 38%.

A facile approach for construction of hierarchical zeolites via kinetics

Abstract It has long been a dream to construct hierarchical zeolites by a really simple and cost-effective method which is feasible in industry. Here we provide an alternative approach in which the crystallization kinetics is regulated by solely changing the added amount of NaOH in the initial gel of a traditional zeolite and then the adjustment of the morphology and structure of the zeolite products is realized. This approach overcomes most of the limitations associated with the popular methods, such as complex operations and costly secondary templates. As an example, hierarchical ZSM-5 zeolite is prepared with using the most common raw materials and synthesis technology which used in the large-scale production of traditional zeolites. The crystallization process of the hierarchical ZSM-5 zeolite is investigated in detail and compared with the microporous zeolite. The results indicate that the increase of NaOH concentration in the synthesis system can enhance the rate of nucleation but the hierarchical pore structure can be formed only under the moderate concentration. The crystallization of the hierarchical ZSM-5 zeolite takes place by a chain of processes: (i) formation of wormlike precursors, (ii) aggregation of the precursors, (iii) condensation of the precursors and formation of internal voids, (iv) formation of external shell layers. The performance studies show that the obtained hierarchical ZSM-5 zeolite possesses significantly enhanced diffusion property and superior ability for catalytic cracking bulky molecules.

Anionic Tuning of Zeolite Crystallization

Zeolites are of great industrial relevance as catalysts, adsorbents, and ion-exchangers and typically synthesized under hydrothermal conditions. Rational regulation of their crystallization process...

Synthesis of Ni-Modified ZSM-5 Zeolites and Their Catalytic Performance in n-Octane Hydroconversion.

Ni-modified ZSM-5 zeolites with different nickel contents were successfully prepared by the in situ synthesis method and the impregnation method. The synthesized samples were characterized by XRD, SEM, N2 adsorption–desorption isothermals, and Py-FTIR. The characterization results show that both the textural properties and crystallization of Ni-modified ZSM-5 zeolites were preserved well, and their acidic properties can be modulated after nickel modification. The corresponding NiMo catalysts supported on Ni-modified ZSM-5 zeolites were prepared by the incipient wetness co-impregnation method, and their catalytic performances were evaluated in n-octane hydroconversion. Compared to the those modified by the in situ synthesis method, ZSM-5 zeolite-supported catalysts modified by the impregnation method exhibit higher stability and higher isomerization selectivity. This is due to the synergistic effect between Brønsted acid sites and Lewis acid sites on the Ni-modified ZSM-5 zeolites, especially for the NiMo/1Ni-Z5 catalyst.

Time-resolved in situ visualization of the structural response of zeolites during catalysis

Zeolites are three-dimensional aluminosilicates having unique properties from the size and connectivity of their sub-nanometer pores, the Si/Al ratio of the anionic framework, and the charge-balancing cations. The inhomogeneous distribution of the cations affects their catalytic performances because it influences the intra-crystalline diffusion rates of the reactants and products. However, the structural deformation regarding inhomogeneous active regions during the catalysis is not yet observed by conventional analytical tools. Here we employ in situ X-ray free electron laser-based time-resolved coherent X-ray diffraction imaging to investigate the internal deformations originating from the inhomogeneous Cu ion distributions in Cu-exchanged ZSM-5 zeolite crystals during the deoxygenation of nitrogen oxides with propene. We show that the interactions between the reactants and the active sites lead to an unusual strain distribution, confirmed by density functional theory simulations. These observations provide insights into the role of structural inhomogeneity in zeolites during catalysis and will assist the future design of zeolites for their applications.

Stable Zn@ZSM-5 catalyst via a dry gel conversion process for methanol-to-aromatics reaction

Abstract A unique synthesis route to stabilize zinc species in ZSM-5 zeolite crystals was developed. Firstly, extensive mesoporosity in ZSM-5 was obtained through alkali treatment, after which Zn nanoparticles were introduced into the hierarchical ZSM-5 by impregnation. Then the sample was mixed with SiO2-sol and shaped. Finally, the Zn-fixed ZSM-5 zeolites was obtained by dry gel conversion. By this method, zinc species can be effectively stabilized in zeolite, which can not only improve the aromatic hydrocarbons selectivity, but also increase the stability of the catalyst in the reaction of methanol to aromatics (MTA). The acidity properties and the state of zinc species were studied. It was found that the catalyst possessed more Lewis acid sites and the ratio of Zn(OH)+/ZnO was increased after dry gel conversion.

Synthesis of ZSM-5 zeolites using palygorskite as raw material under solvent-free conditions

Zeolites have extensively been applied in gas adsorption and separation, catalysis, and ion exchange thanks to their numerous interesting features. However, the synthesis of zeolites usually requires solvents, which often lead to water pollution, loss of silicon and aluminium components, and low synthesis efficiency. In this account, ZSM-5 zeolites were synthesized from natural clay palygorskite (PAL) by acid leaching, followed by thermal treatment under solvent-free conditions. The as-obtained ZSM-5 zeolites exhibited high crystallinity and mesoporous structure. The NMR spectra of ZSM-5 zeolites confirmed the presence of aluminium element derived from the acid-treated PAL (APAL) existed in zeolite framework. Thus, PAL was simultaneously employed as silica and aluminium sources for zeolite preparation. The Si/Al molar ratio of ZSM-5 zeolites could be adjusted by adding NaAlO2, but against growth of ZSM-5 zeolites, resulting in formation of analcime. On the other hand, long thermal treatment for 72 h caused the dissolution of ZSM-5 zeolite crystals and formation of analcime. Overall, calcination could enhance the activity of APAL and crystallinity of ZSM-5 zeolites, and solvent-free synthesis of zeolites from clay might efficiently reduce the cost of zeolites.

The Synthesis of Monodisperse MFI Nanozeolites: Controlling the Crystallization Process

The sinthesis conditions of a series of monodisperse crystals of ZSM-5 zeolite, silicalite-1, and Fe-silicalite-1 with an average particle size in the range of 30 to 450 nm have been determined. The kinetic features of the silicalite-1 crystallization at low temperatures (60−90°C) and atmospheric pressure have been studied. The effective activation energies of silicalite-1 nucliation and crystal growth have been determined to be 95 ± 7 and 100 ± 7 kJ/mol, respectively. The influence of the synthesis time and temperature as well as the silicon source concentration on the size of the MFI type nanocrystals has been studied.

Solvent-free crystallization of ZSM-5 zeolite on SiC foam as a monolith catalyst for biofuel upgrading

Conventional synthesis of monolith-supported zeolite catalysts is based on a hydrothermal strategy. Here, we report a solvent-free crystallization process to coat ZSM-5 zeolite crystals on a monolithic SiC foam with a honeycomb structure (ZSM-5/SiC). Characterizations of the ZSM-5/SiC by scanning electron microscopy, N2 sorption, and X-ray diffraction indicate that the zeolite sheath has been ideally coated on the surface of the SiC foam with high purity and crystallinity. Fixing Pd nanoparticles within the ZSM-5 zeolite crystals delivers a bifunctional Pd@ZSM-5/SiC catalyst, which exhibits high activity and selectivity toward diesel range paraffins in the hydrodeoxygenation of methyl oleate, a model molecule for biofuel. In comparison to the powder Pd@ZSM-5, the Pd@ZSM-5/SiC monolith catalyst shows more efficiency, which is attributed to the fast mass transfer and high heat conductivity on the honeycomb SiC structure. The durability test indicates that the Pd@ZSM-5/SiC catalyst is stable under the reaction and high-temperature regeneration conditions.

Seed-Assisted Synthesis and Catalytic Performance of Nano-sized ZSM-5 Aggregates in a One-Step Crystallization Process

Hierarchical nano-sized ZSM-5 aggregates were successfully synthesized via a seed-assisted method in the presence of cetyltrimethylammonium bromide (CTAB) through a facile one-step crystallization process. Commercial ZSM-5 zeolites with a SiO2/Al2O3 ratio comparable to that of ZSM-5 products were treated with alkali and used as the seed particles. The influences of crystallization conditions were investigated, and the possible synthesis mechanism was proposed. ZSM-5 zeolites with different amounts of CTAB added were characterized using many techniques and evaluated in toluene alkylation with methanol. The results showed that a trace amount of CTAB significantly promoted the crystallization of ZSM-5 zeolite, with the morphology changing from hexagonal-shape crystals to uniform spherical aggregates. CTAB may act as the structure-directing agent and assemble the primary crystallites to generate hierarchical ZSM-5 aggregates. The ZSM-5 zeolite with the smallest primary particles of 50–80 nm exhibited large specific surface area, abundant mesopores, and the greatest microporosity. The hierarchical nano-sized ZSM-5 aggregate showed higher toluene conversion and a longer lifetime without compromising the selectivity to xylene and p-xylene in toluene alkylation with methanol.

Untangling the role of the organosilane functional groups in the synthesis of hierarchical ZSM-5 zeolite by crystallization of silanized protozeolitic units

Abstract Crystallization of hierarchical ZSM-5 zeolite has been performed under hydrothermal conditions from silanized protozeolitic units. The role of amine and phenyl groups present in the organosilanes, as well as the use of dipodal silanization agents, on the creation of mesoporosity in the zeolite samples has been investigated. The presence of amine groups and dipodal moieties in the organosilane increases their interactions with the protozeolitic nanounits in the gel, which results in hierarchical zeolites showing enhanced secondary porosity and a higher degree of modification of the textural properties. Nevertheless, dipodal organosilanes hinder strongly the aggregation of the nanounits, leading to non-completely crystalline materials. In contrast, the combination of phenyl and amine groups into a single organosilane has shown to be effective for the generation of more uniform mesopores. Thus, N-(2-N-Benzylaminoethyl)-3-aminopropyltrimethoxysilane (Ph-2A) has been found as the best silanization agent, affording a hierarchical zeolite with a narrow mesopore size distribution and a high concentration of strong Bronsted acid sites. Moreover, during LDPE catalytic cracking in TGA tests, the latter material allowed the conversion of the polymer to occur in a narrow temperature range as a consequence of its more uniform acid and textural properties. Likewise, this sample exhibited a high activity in LDPE cracking at 340 °C using a laboratory scale reaction system to produce mainly gasoline-range hydrocarbons and light olefins.

Crystal engineering of hierarchical zeolite in dynamically maintained Pickering emulsion

Crystal engineering of hierarchical zeolites is regarded as a promising way to enhance diffusion-dependent catalytic properties of zeolitic materials. Crystallization process control on crystal size and pore-structure is desirable over porogen based protocols and post-synthetic methods for the low cost, high yield and potential scalability. Herein, a tumbling crystallization of hierarchical ZSM-5 zeolite in immiscible water/toluene Pickering emulsion inspired by energy dissipating structure occurring in nature is presented. The structure and acid properties of the obtained hierarchical material have been revealed using a panoply of characterization techniques such as powder X-ray diffraction, N2 physisorption isotherms, SEM, TEM, mercury protrusion measurements, NH3-TPD and pyridine IR spectroscopy, showing that the material contains high crystallinity, and penetrating macropores. Crystallization is found to proceed through a Pickering emulsion structure maintained by emulsifying effect of constant tumbling. Such an emulsion structure has hindered attachment growth of primary nanocrystals formed at the nucleation stage to further grow into larger size via coalescense. The hierarchical zeolite exhibits architecture-dependent prolonged catalyst lifetime and light olefin yield in dimethylether-to-olefin conversion. This process control to generate hierarchical zeolites opens up new ways toward inexpensive, high level control and efficient engineering of zeolite morphology.