ZSM-5 Particles Research Articles

Insight into seed-assisted template free synthesis of ZSM-5 zeolites

Synthesizing nanocrystalline ZSM-5 using a templating method is considered to be time, energy, and materials inefficient. In addition, the production of CO2 from the calcination process has a negative impact on the environment. Therefore, finding another method to synthesize nanocrystalline ZSM-5 without using an organic template would be beneficial. Here, nanocrystalline ZSM-5 was synthesized successfully in high yield by using a seed-assisted method and without using the organic template. In addition, the effects of synthesis temperature, synthesis time, pH, amount of seeds, size of seeds, aging time, and use of calcined and uncalcined seeds were investigated. The synthesized nanocrystalline ZSM-5 materials were characterized by using X-ray diffraction (XRD), gas adsorption isotherm (BET/BJH), inductively coupled plasma optical emission spectroscopy (ICP/OES), and transmission electron microscopy (TEM). It was found that the synthesis temperature and time have a strong influence on the crystallinity of the synthesized nanocrystalline ZSM-5. Under the conditions reported here, the ideal synthesis temperature and time to synthesize fully crystalline ZSM-5 crystals are 165 °C, and 14–24 h, respectively. Controlling the pH and seed amount facilitated the synthesis of ZSM-5 with high crystallinity. A basic environment with Na2O/SiO2 = 0.4, and a seed amount of 0.35 wt % were necessary to form fully crystalline ZSM-5 particles. In addition, ZSM-5 with high crystallinity and yield could be obtained using calcined seeds. Finally, seeds with large complex aggregates showed a strong influence on the size and aggregation of the synthesized particles.

Effect of Particle Morphology for ZSM-5 Zeolite on the Catalytic Conversion of Methanol to Gasoline-Range Hydrocarbons

ZSM-5 zeolite composed of nano-sphere or nano-rod crystallites were prepared to compare with micron-sized ZSM-5. These samples have different morphologies but similar acid properties, which could diminish the effect of acid properties to study the morphology effect of ZSM-5 particles on MTG reaction. It was found that nano-sphere crystallite aggregate ZSM-5 presented larger external surface and mesopore volume than micron-sized ZSM-5 and nano-rod crystallites aggregate ZSM-5, increasing both acid sites accessibility and diffusion properties. Add that into the consideration with the weak acidity, nano-sphere crystallite aggregated ZSM-5 exhibited high liquid hydrocarbon yield, slow deactivation process and high selectivity to aromatics and iso-paraffins.

Structural and Textural Characteristics of Zn-Containing ZSM-5 Zeolites and Application for the Selective Catalytic Reduction of NOx with NH3 at High Temperatures

Zinc-containing MFI-type ZSM-5 zeolites were synthesized with ammonia coordinated zinc solution as zinc source, n-butyl amine as template and ZSM-5 as seeds by a facile one-step hydrothermal method, which exhibited outstanding performance for selective catalytic reduction NO with NH3 over a wide temperature range. The powder X-ray diffraction detected results showed that there was no other crystalline phase except for ZSM-5 phase and IR analysis suggested that the zinc had successfully incorporated into the zeolite framework was the vibration absorption peak at 1080 and 1230 cm−1 were broadened, which were assigned to asymmetric stretching of Si–O–Si. With the amount of zinc increases, big changes of morphologies, specific area and pore volume occurred which were collected by scanning electron microscope and Brunauer Emmett Teller Method. And the content of zinc species in the synthesized system was able to coordinate the growth size of the crystal. Furthermore, the addition of seeds would basically effectively prohibit the twin growth among these Zn-containing ZSM-5 crystals was firstly brought forward. Schematic diagrams of (A) Mono-dispersed ZSM-5 particles (B) Twin growth ZSM-5 particles.

Enhanced CO2/CH4 separation properties of asymmetric mixed matrix membrane by incorporating nano-porous ZSM-5 and MIL-53 particles into Matrimid®5218

Asymmetric Matrimid/fillers mixed matrix membranes, composed of a metal organic framework (MIL-53; with CO2 sorption properties) and a zeolite (ZSM-5; with size selective properties) as porous fillers, were used in CO2/CH4 separation. Cross-sectional SEM images of membranes showed a complete porous structure with finger-like pores. The presence of 6 wt. % of ZSM-5 in membrane matrix led to the CO2/CH4 selectivity enhancement. Conversely, results obtained from gas permeance tests (i.e., pure and mixed gas test) conducted over those membranes which contain higher loading percentage, showed the increase of permeation along with selectivity decline. Creation of interfacial voids between polymer and particles at higher loading of ZSM-5 caused the performance failure of membrane and selectivity was decreased, too. Alternatively, those membranes incorporated with MIL-53 particles, compared to pure Matrimid, showed significant enhancement in permeance of gases and CO2/CH4 selectivity. Organic linkers of MIL-53 improve the quality of polymer–filler interfaces and decrease the probability of the formation of interfacial voids as much as possible, which resulted in membrane performance enhancement. In pure permeation, CO2 permeance showed 270% growth and CO2/CH4 selectivity increased from 14.8 to 23.6 in membranes containing 15 wt. % MIL-53 compared to pure asymmetric Matrimid. MMMs filled with MIL-53 particles were suggested more proper separation factor compared to those embedded by ZSM-5 particles. The superior performance of Matrimid/MIL-53 MMM was attributed to the quality of polymer/filler interfaces as well as selective CO2 adsorption with embedded MIL-53. The best CO2 permeance and CO2/CH4 selectivity gained by Matrimide/MIL-53 at 3 bar were 46 GPU and 23.6 respectively; where Matrimid/ZSM-5 exhibited a CO2 permeance of 14.5 GPU and CO2/CH4 selectivity of 15.6. As the feed pressure increased from 3 to 12 bar, the permeance of both gases in MMMs decreased and CO2/CH4 selectivity increased, too. The increase of operating temperature from 35 to 65 °C resulted in enhancement of gas permeance, while CO2/CH4 selectivity decreased. Various permeation models (i.e., Maxwell, Bruggeman and Lewis–Nielsen) were used to predict mixed matrix membranes' separation properties. All models showed appropriate compatibility with experimental data at lower particles loading.

Synthesis of zeolite@metal–organic framework core–shell particles as bifunctional catalysts

A zeolite@metal–organic framework (ZSM-5@UiO-66) core–shell composite has been synthesized for the first time by solvothermal growth of UiO-66 on the surface of ZSM-5 particles. The acidity from ZSM-5 and the basicity from the amine groups in UiO-66 obtained by post-synthetic modification of the metal clusters, endow a bifunctionality on ZSM-5@UiO-66 for cascade reactions.

Core–shell Pd/ZSM-5@ZIF-8 membrane micro-reactors with size selectivity properties for alkene hydrogenation

A well-designed Pd/ZSM-5@ZIF-8 core–shell structure has been prepared by application of a combination of seed-induction synthesis strategy and self-assembly synthesis techniques. First, uniform ZSM-5 particles with micron size and high crystallinity were prepared from organic-template-free gel systems containing 200nm ZSM-5 seeds and exchanged with Pd(NO3)2 aqueous solution. Then incompatibility between the Pd/ZSM-5 core material and ZIF-8 shell precursor was circumvented by surface modification using a layer by layer self-assembly of polyelectrolyte, followed by a subsequent two-step temperature synthesis process inducing the formation of continuous and well-intergrown ZIF-8 shell. Thickness of ZIF-8 shell can be simply tuned by monitoring the assembly cycles. Furthermore, hydrogenations of 1-hexene and cyclohexene were chosen as model reactions to evaluate the catalytic behavior of the Pd/ZSM-5@ZIF-8 core–shell architecture and tert-dodecylthiol was used as a poison to test its anti-poisoning ability. Results show that such core–shell architecture exhibits excellent poison resistance and selectivity control properties for the hydrogenation reactions and can be potentially used as a membrane reactor in the field of heterogeneous catalysis.

The relationship between sub-micrometer sized ZSM-5, slice-like (lamellar) keatite and hollow α-quartz particles: a phase transformation study

Crystallization–transformation processes in the reaction mixture: (4Na2O–0.1667Al2O3–100SiO2–4000H2O) seeded with 4 wt% of 260 nm silicalite-1 seeds, at 170 °C were investigated by various experimental methods such as, X-ray diffraction (XRD), electron diffraction (ED), scanning-electron microscopy (SEM), transmission electron microscopy (TEM), particle size analysis (PSD), pH measurement, atomic absorption spectrometry (AAS) and dynamic light scattering (DLS). Analysis of the obtained results have shown that the crystallization–transformation takes place by a chain of processes: (i) dissolution of amorphous silica (used as silica source), and formation of 10–50 nm precursor species (PSs), (ii) spending of the PSs for both the limited growth of zeolite ZSM-5 on the surfaces of silicalite-1 seed crystals and formation of worm-like particles (WLPs), (iii) formation of condensed aggregates (CAs) by aggregation/condensation of the WLPs; a part of the composite particles, composed of the silicalite-1 core and ZSM-5 shell are incorporated into CAs, (iv) nucleation of keatite followed by solution-mediated transformation of the condensed WLPs into lamellar keatite, (v) nucleation of α-quartz followed by solution-mediated transformation of keatite into α-quartz; a part of the nuclei of α-quartz are formed on the surface of the core–shell silicalite-1–ZSM-5 composite species and another part of the nuclei are formed in the vicinity of the dissolving keatite and (vi) dissolution of the silicalite-1 core and a major part of the ZSM-5 “interlayer” of the composite particles (α-quartz shell-ZSM-5 “interlayer”-silicalite-1 core) and formation of hollow α-quartz particles with a thin ZSM-5 layer on the inner surfaces of the hollow α-quartz particles. Occurrences of all the mentioned processes are rationally analyzed and explained on the basis of the existing and newly obtained knowledge.

Novel Gradient Porous ZSM-5 Zeolite Membrane/PSSF Composite for Enhancing Mass Transfer of Isopropanol Adsorption in a Structured Fixed Bed

A novel gradient porous ZSM-5 membrane/PSSF (paperlike sintered stainless steel fiber) composite was prepared by the wet layup papermaking/sintering technique and a secondary growth process. The effects of crystallization time on the morphology, thickness, and Si/Al ratio of the ZSM-5 membranes were studied. The composites were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and N2 adsorption. Adsorption behaviors of isopropanol in structured fixed beds filled with granular activated carbon (GAC) or ZSM-5 particles in the inlet of the bed and ZSM-5/PSSF composites in the outlet of the bed were investigated. Adsorption breakthrough behaviors of isopropanol in fixed beds containing only GAC or ZSM-5 particles were also studied. Theoretical breakthrough curves were predicted using the Yoon–Nelson model and compared with the experimental results. Satisfactory agreement between the theoretical breakthrough curves and the experimental dat...

Organic template-free synthesis of ZSM-5 zeolite particles using rice husk ash as silica source

ZSM-5 zeolite particles were synthesized through in-situ extraction of silica from rice husk ash in the absence of organic template by a simple hydrothermal condition at 150°C/72–96h. The powders were characterized by XRD, TGA, DTA, FTIR, N2 physisorption studies, and field emission scanning electron microscopy (FESEM). Crystallization of ZSM-5 started at 150°C/72h. The vibration bands at around 540 and 1220cm−1 indicated the presence of characteristic double 5-ring of ZSM-5. The BET surface area and pore volume increased with increase in synthesis time from 72 to 96h at 150°C. FESEM images showed coffin-shaped morphology of ZSM-5 particles.

On the location, strength and accessibility of Brønsted acid sites in hierarchical ZSM-5 particles

Microporous and mesoporous (hierarchical) ZSM-5 samples, prepared by desilication, dealumination and templating with carbon nanoparticles have been characterized by adsorbing benzene, cyclohexane and 1,3,5-trimethylbenzene (mesitylene) to probe the location, the strength and the accessibility of Brønsted acid sites. The mesoporosity introduced by the methods explored resulted in a statistical accommodation of benzene at the channel intersections. Cyclohexane showed the highest strength of physisorption in micro- and mesopores and, thus, probes the largest fractions of acid sites. Mesitylene adsorption showed that mesopores of hierarchical zeolites do not contain Brønsted acid sites. All results indicated that the mesoporosity influences only the accessibility of the acid sites in the ZSM-5 crystals mostly via shortening diffusion pathways, but not the strength of the interaction with the cyclic hydrocarbons. The enhanced transport rates observed for benzene are associated to the decreased pore length inside the mesoporous particles, rather than to changes of the pore structure or the generation of additional sites.

Preparation of Small Crystalline ZSM-5 and its Application in Conversion of Methanol to Aromatic

Small crystalline ZSM-5 was synthesized by a hydrothermal synthesis procedure and was characterized by XRD, SEM and N2-absorption. The results show that small crystalline ZSM-5 particles grow into larger agglomerates with a diameter of 100-400 nm, resulting in mesopore and higher surface area. During conversion of methanol to aromatics, small crystalline ZSM-5 catalyst performances better than micron-size ZSM-5 catalyst in aromatic selectivity and lifetime. The aromatic selectivity could reach to 21.7%, and the small crystalline ZSM-5 catalyst shows no deactivation during first 24h.

Host–Guest Geometry in Pores of Zeolite ZSM‐5 Spatially Resolved with Multiplex CARS Spectromicroscopy

Pore relations: Reagent molecules form head-to-tail chains in the pores of ZSM-5 zeolite particles in the presence or absence of acidic sites, according to multiplex coherent anti-Stokes Raman scattering spectromicroscopy (mCARS). The molecular ordering in the pores makes it possible to characterize the crystallographic subunits of individual ZSM-5 particles with (sub)micrometer spatial resolution in three dimensions.

Tuning the hydrophobicity of ZSM-5 zeolites by surface silanization using alkyltrichlorosilane

ZSM-5 zeolites were modified with alkyltrichlorosilanes of various chain lengths (octyltrichlorosilane, decyltrichlorosilane, dodecyltrichlorosilane and hexadecyltrichlorosilane) and characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Thermal gravimetric analysis (TGA) and contact angle measurements (CA). The results showed that a closely packed and hydrophobic layer was presented at the particles surface and the surface wetting property varied from hydrophilic to hydrophobic, even to superhydrophobic. It was interesting to notice that the hydrophobic properties of modified ZSM-5 particles could be tuned by varying the chain length of chlorosilane and changing the pretreatment temperature before silanization. With increasing the alkyl chain length of trichlorosilane, the hydrophobicity increased. However, with an increase in the pretreatment temperature, the hydrophobicity decreased. Moreover, the relationship between the wetting properties and thermal stability was also investigated, the results showed that the modified ZSM-5 particles possessed good hydrophobicity at a temperature below 250 °C in air. These modified ZSM-5 particles may be utilized for many potential applications, such as membrane fillers, selective adsorbents, catalysts, chromatographic supports and so on.

Improved performance of PDMS/ceramic composite pervaporation membranes by ZSM-5 homogeneously dispersed in PDMS via a surface graft/coating approach

A homogeneous dispersion of inorganic fillers in polymer matrix is a primary challenge for the advancement of mixed matrix membranes (MMMs) in pervaporation and gas separation. In this work, a surface graft/coating approach was developed for homogeneously dispersing ZSM-5 zeolite in polydimethylsiloxane (PDMS) for preparing ZSM-5 filled PDMS mixed matrix/ceramic composite membranes. Molecular dynamics simulations were carried out to calculate the interaction energy between zeolite and PDMS. It was found that surface modification of zeolite particles could highly improve their interaction with PDMS matrix. The SEM images confirmed the uniform dispersions of surface-modified ZSM-5 particles in PDMS matrix even at highest zeolite loading of 40 wt.%. As revealed in the FT-IR analysis and contact angle measurements, the prepared ZSM-5 filled PDMS membranes exhibited less hydroxyl groups and became more hydrophobic with increasing zeolite loading. The pervaporation experiment in 5 wt.% ethanol–water solution indicated that the homogeneously incorporated ZSM-5 particles improved the selectivity of PDMS membrane, and the separation factor of surface-modified ZSM-5 filled PDMS membrane increased gradually with zeolite loading. This effective dispersion method could be instructive for the fabrication of organic–inorganic composite materials.

Fabrication and characterization of polysulfone/polyimide–zeolite mixed matrix membrane for gas separation

In this study the gas separation performance of polyimide/polysulfone (PI/PSF) mixed matrix membranes filled with zeolite ZSM-5 particles is investigated. The membranes are prepared by solution-casting method and utilized to determine the permeation rates of N 2, O 2, CO 2 and CH 4 through pure polymers as well as composite membranes. The membranes are characterized by SEM, TGA and FTIR. The effects of polymers ratio and weight fraction of zeolite on permeation and selectivity of the gases are discussed. Polymers ratio in the mixed matrix have assumed values of 100% PSF, 70/30 (PSF/PI), 50/50, 30/70 and 100% PI while ZSM-5 loadings are varied between 0 and 20 wt.%. SEM results showed that fabricated membranes have homogeneous structure. With pure polyimide membrane, O 2 permeability increased from 0.69 Barrer for membrane without zeolite up to 0.73 and 0.89 Barrer for membranes with 10% and 20% zeolite, respectively. Within blended matrices, the minimum permeability (maximum selectivity) and the most homogeneous matrix structure were related to the matrix with 50/50 weight percent of two polymers.

Anionic emulsion-directed synthesis of zeolite ZSM-5 with tunable morphology and Si/Al ratio

Zeolite ZSM-5 was synthesized for the first time in an anionic emulsion system composed of sodium dodecylbenzene sulfonate, pentanol, cyclohexane and zeolite synthesis mixture, and subsequently characterized by XRD, SEM, FTIR, TG and N2 adsorption techniques. It is found that altering emulsion composition and adding electrolyte can effectively change the morphologies and/or Si/Al ratios of the ZSM-5 samples. Besides the commonly seen coffin morphology, ZSM-5 particles with rare elliptic cylinder, column and ellipsoid morphologies are also obtained. Depending on the weight ratios of anionic surfactant and zeolite reaction mixture, the framework Si/Al ratios of ZSM-5 samples vary slightly. Investigations on the crystallization process further show the emulsion system can induce rapid crystallization by virtue of shortening the induction time. The ways that the emulsion system affects zeolite crystallization, framework Si/Al ratio and particle morphology are tentatively discussed.

A comparative study of diffusion of benzene/p-xylene mixtures in MFI particles, pellets and grown membranes

The transport and separation of mixtures between benzene and p-xylene in pellets prepared by pressing of ZSM-5 powder and a dense supported (crystalline) Silicalite-1 membrane were compared to isolated ZSM-5 crystallites. The kinetics of the transport in the pressed pellet and the grown membrane determined in a Wicke–Kallenbach cell (313–403 K; partial pressure range 200–2300 Pa) differed significantly from those measured for isolated ZSM-5 particles with the pressure modulation frequency response technique (343–403 K; partial pressure 30 Pa). In a pressed pellet, the transport was of Knudsen type leading to high fluxes of 10 −4 mol/m 2 s and identical permeances for benzene and p-xylene. The diffusion coefficient in a pressed pellet exceeded that in particles, in which the transport was controlled by intracrystalline diffusion and the pore entrance step, by 8 orders of magnitude. The flux across a grown Silicalite-1 membrane was two orders of magnitude lower and the permeability of p-xylene was 2.6–5 times higher than that of benzene. The change in diffusivity in the membrane compared to the particles results from the higher surface coverage of p-xylene.

Preparation of discrete colloidal ZSM-5 crystals with high Al-content

A new method for synthesis of discrete colloidal ZSM-5 particles with SiO2/Al2O3 M ratios as low as 30 and sizes .4–1 micrometer has been developed. The relation between the synthesis parameters and synthesis yield, crystal structure, crystallinity, particle size and morphology was investigated. The synthesis yield increases and the deviation of the SiO2/Al2O3 ratio in the product from that in synthesis mixture decreases with increasing autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that temperature determines the lower limit of the SiO2/Al2O3 ratio. The SiO2/Al2O3 ratio in the synthesis mixture decreases with autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that the temperature determines the lower limit of SiO2/Al2O3 ratio. Synthesis mixture, aimed to yield a high SiO2/Al2O3 ratio, gives smaller zeolite crystals, higher specific surface areas, higher geometric areas (external surface area of the crystals) and a more oval crystal shape compared with lower ratios, synthesised at the same temperature. Higher autoclave temperature during the synthesis gives larger zeolite crystals and a more hexagonal crystal shape compared with zeolites synthesised at lower temperatures, for the same SiO2/Al2O3 ratios.

Synthesis of ZSM-5 hierarchical microsphere-like particle by two stage varying temperature crystallization without secondary template

In the present paper, Hierarchical ZSM-5 microsphere-like particles (ZSM-5-HM) were successfully synthesized by separate hydrolysis combined two stage varying temperature crystallization (SHTSVTC) without any secondary template. XRD, SEM and TEM analysis revealed that the ZSM-5-HM particles were 300–600nm in size and constructed by primary ZSM-5 nanocrystals of 30–50nm. The BJH pore size based on the N2 adsorption isotherm and desorption isotherm was 9.7nm and 9.4nm, respectively. For comparison the synthesis was carried out by the constant temperature crystallization (CTC) and two stage varying temperature crystallization methods (TSVTC) under cohydrolysis, respectively. A time trial growth study was conducted for insight into the growth of the hierarchical ZSM-5-HM. It is suggested that the growth of ZSM-5-HM products involves aggregation and assembly combined crystallization process. The synthesis by the TSVTC method gave rise to similar hierarchical ZSM-5 particles when the second stage crystallization time was extended for more 24h. It indicates that the TSVTC is mainly responsible for the formation of the ZSM-5-HM products but the separate hydrolysis can reduce the crystallization time. The demonstrated facile and highly effective approach to mesoporous zeolites can be extended to the synthesis of other zeolites with unique hierarchical structure.

Formation of Al-rich nanocrystalline ZSM-5 via chloride-mediated, abrupt, atypical amorphous-to-crystalline transformation

The efficient hydrothermal synthesis of highly crystalline, nano ZSM-5 particles, rich in framework Al content (Si/Al = 25) and low in the degree of intergrowth, in a medium of unusually high NaCl concentration was followed by examining the solids formed with 29Si, 27Al, 13C MAS NMR, TEM, DRIFT, and XRD spectroscopies. ZSM-5, in the form of 60 nm primary crystallites present as 100–150 nm dispersed cubic clusters, were crystallized from an amorphous phase via an abrupt, solid state transformation within 15 min at 165 °C. A model of the crystallization process was proposed, different from the typical nucleation-crystal growth process, in which aluminosilicate oligomers of low connectivity was salted out as amorphous solid as a result of high NaCl concentration immediately upon mixing of the ingredients.