Structural, compositional and acidic characteristics of nanosized amorphous or partially crystalline ZSM-5 zeolite-based materials (original) (raw)
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Microporous and Mesoporous Materials, 2012
In this work, the influence of alkalinity, A = [Na 2 O/H 2 O] b (b = batch), of the reaction mixture on structural, particulate, morphological and chemical properties of the crystalline end products obtained by hydrothermal treatment (heating at 483 K for 2 h) of the TPA-free reaction mixture: 1.0Al 2 O 3 /100SiO 2 / xNa 2 O/4000H 2 O seeded by silicalite-1 nanocrystals (260 nm, 4 wt.% of silica in gel mixture), was investigated by different characterization methods such as powder X-ray diffraction (XRD), scanning-electron microscopy (SEM), particle size distribution (PSD) measuring by laser light scattering (LLS) and X-ray fluorescence (XRF). The obtained results showed that, when silicalite-1 having the size of 260 nm was used as seed, fully crystalline product (silicalite-1/ZSM-5) having the size in the range of 400-600 nm and Si/Al ratio of 10-18 can be obtained for 0.006 6 A 6 0.01, in less than 2 h. However, the product obtained at low (A 6 0.005) or high (A P 0.011) alkalinities possess amorphous and/or phillipsite impurities, respectively. The influence of alkalinity, A, on the mentioned properties of the crystalline end product was discussed in relation to the influence of alkalinity on the relevant critical process of zeolite ZSMcrystallization in the absence of organic templates.
Synthesis and characterization of partially crystalline nanosized ZSM-5 zeolites
Ceramics International, 2013
Partially crystalline nanosize ZSM-5 with high surface area (678 m2/g) was synthesized successfully without using organic template by a two-step temperature process. Aluminum nitrate was used as aluminum source for the first time to synthesize ZSM-5 materials. The presence of MFI structure of the materials was analyzed by XRD, FTIR, Raman spectroscopy and TEM techniques. Addition of commercial HZSM-5 as a seeding agent to the reactants resulted an increase in crystallinity of the ZSM-5 sample and subsequent decrease in specific surface area. The partially crystalline samples exhibited low microporosity and remarkably high meso/macropore volume with pore diameters around 30 nm
CrystEngComm, 2011
Mesoporous ZSM-22 zeolite (TON structure) is prepared by controlled silicon extraction in aqueous NaOH under different conditions of concentration, temperature, and time. The first challenge is to synthesize a pure ZSM-22 sample, since ZSM-5 and cristobalite impurities are hard to avoid. For this purpose, hydrothermal syntheses in autoclaves of 30-1000 cm 3 using tumbling or magnetic mixing were conducted. The parent (calcined) and alkaline-treated samples are characterised by XRD, AAS, N 2 and Ar adsorption, TEM, 27 Al MAS NMR, and FTIR. The introduction of mesoporosity in ZSM-22 crystals is not straightforward due to their peculiar characteristics: the rod-like morphology of their small crystallites, the one-dimensionality of the ellipsoidal micropore system, and an uneven Al distribution. Compared to other zeolite frameworks such as MFI, the generation of up to 95 m 2 g À1 of (both inter-and intracrystalline) mesopore surface area by NaOH treatment leads to a sizeable drop of the micropore volume (down to 0.006 cm 3 g À1 ), attributed to blocking by re-deposited Al species. A subsequent mild acid treatment in aqueous HCl restores ca. 90% of the original micropore volume and increases the mesopore surface area to 114 m 2 g À1 . However, due to the particular Al distribution in the parent ZSM-22 crystals, only 37% of the original Brønsted acidity is recovered. A new descriptor 'desilication efficiency' is introduced to relate the mesopore area generated to the mass of zeolite dissolved. In the case of ZSM-22 nanorods and ferrierite platelets, the desilication efficiency is relatively low compared to ZSM-5, most likely due to the crystal morphology of the former two zeolites. The auxiliary mesoporosity developed in ZSM-22 brings new prospects to catalytic applications of the zeolite due to the extensive creation of pore mouths in the hierarchical sample.
Applied Nanoscience, 2014
The synthesis of analcime and nanosized ZSM-5 zeolites was carried out by a hydrothermal method with silica extracted from rice husk, available as an inexpensive local biowaste, and without the use of an extra alumina source. Amorphous silica (with 88 wt% of SiO 2 ) was extracted from rice husk ash by a suitable alkali solution. The effects of crystallization temperature, time and SiO 2 / Al 2 O 3 ratio of the initial system on the properties of final products were investigated. For the characterization of the synthesized product, X-ray diffraction, scanning electron microscope, energy dispersive X-ray techniques, Fourier transform infrared and Brunauer-Emmett-Teller method were applied. Crystallinity percentages of analcime and nanosized ZSM-5 were 95.86 and 89.56, respectively, with specific surface area of 353.5 m 2 g -1 for ZSM-5. The experimental results revealed that the synthesis of analcime and nanosized ZSM-5 zeolites was more practical with using silica extracted from inexpensive raw materials, while the whole crystallization process was accomplished without adding any alumina source during.
Some Observations on the Synthesis of Fully-Dispersible Nanocrystalline Zeolite ZSM-5
Journal of Nanoscience and Nanotechnology, 2014
A facile method for the rapid synthesis of fully-dispersible ZSM-5 (Si/Al = 100) of about 30 nm size in high yield (about 91%) is described. The method comprises three steps, viz., concentration of an initial clear solution, low-temperature (80 C) ageing of concentrated sol, and high-temperature (175 C) hydrothermal treatment or microwave heating (175 C) of aged concentrated sol A simple vacuum-concentration method was used for the extraction of pure NPs of ZSM-5 in solution. XRD, FT-IR, TGA and ASAP characterizations showed that the NPs were partially crystalline. The concentration step accelerated the aggregation of primary units, which helps in the production of a large number of nucleation centers protected by TPA + ions against aggregation. During low-temperature ageing, the number of critical sized nuclei increases, growing into zeolite. The high-temperature heating results in the complete growth of unreacted silica, giving high yields. A key factor for generating small non-aggregated zeolite crystals is the amount of water in the synthesis sol. The threestep method presented here produces a target material of small and uniform sized, non-aggregated ZSM-5 of about 30 nm in a short reaction time. The results are significant, as the synthesis method adopted here produces much uniform, non-aggregated nanocrystalline ZSM-5 in a shorter time with high yield.
Preparation and characterization of ZSM-5 zeolite
International journal of computational and experimental science and engineering, 2023
The research for new energy sources has promoted hydrocarbon production from biomass and solid wastes over ZSM-5 zeolites. The metal incorporation by different methods has led to a variety of chemical applications. In this way, the combination of the shape selectivity and acidity properties of the pentasil zeolites with the activity of metal oxide under different environments may influence the product distribution in diverse catalytic reactions. In this work, ZSM-5 zeolites were prepared by hydrothermal synthesis employing aluminum nitrate and AIP as aluminium sources and TPAOH as structure director agent at atmospheric pressure and low temperature (90 ºC). In addition, these materials were modified with iron and titanium cations by direct synthesis at 170 °C and autogenous pressure to promote the crystallinity. The characterization of the samples was performed by XRD, XRF, SEM, TPD-NH 3 and nitrogen adsorption. It was observed that the use of AIP and the metal incorporation decreases the crystallinity of the zeolites under synthesis conditions, which leads to increase the specific area value in the BET because of the presence of amorphous material. On the other hand, acidity of the modified zeolites was found to be lower than that of ZSM-5 zeolite.
Chemistry of Materials, 2009
Surface-passivating silanization of protozeolitic units has been shown to be an effective strategy for the preparation of ZSM-5 nanocrystals, showing a controlled aggregation degree and a hierarchical porosity. ZSM-5 zeolite materials are thus obtained with adjustable and relatively uniform mesoporosities that have a strong influence on resulting macroscopic reaction properties, especially for macromolecular reagents. The mean sizes of the nanounits and, therefore, the textural and accessibility of these materials can be varied by changing the precrystallization conditions and the concentration of the seed-silanization agent. In addition to conventional characterization techniques, solid-state two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy measurements and the application of the NLDFT model to the argon adsorption isotherms have allowed both the local and the mesoscopic compositions, as well as the structures of the hierarchically porous ZSM-5 materials, to be established. The resulting combination of mesopore sizes and exterior-nanocrystal surface properties of the hierarchically structured ZSM-5 zeolites is shown to catalyze reactions that are otherwise limited by steric and/or diffusional limitations, as demonstrated by their enhanced activity for polyethylene cracking.
Micro/mesoporous aluminosilicate composites from zeolite MCM-22 precursor
Microporous and Mesoporous Materials, 2007
Micro/mesoporous aluminosilicate composites were prepared applying a two-step hydrothermal synthesis procedure. In the first step a zeolitic component, i.e., the precursor of zeolite MCM-22 was synthesized and its swollen and partially delaminated derivatives were prepared. In the second step mesoporous MCM-41 silicate was synthesized in a slurry of the above MCM-22 type precursor from additional silicate source and using hexadecyltrimethylammonium bromide (CTMABr) template. The structure, morphology and the acidic properties of the obtained composite materials were characterized by X-ray diffraction, infrared spectroscopy, N2 adsorption isotherms, and electron microscopy (SEM and TEM). The results suggest that the composite materials were built from nanosize, randomly orientated stacks of thin layers of MCM-22 type zeolite and of mesoporous silicate MCM-41 material. The catalytic activity of the composite material was compared to that of the zeolite MCM-22 in the hydroconversion of heptane.
Synthesis of ZSM−5 zeolite using Bayat natural zeolite as silica and alumina source
AIP Conference Proceedings
Zeolite ZSM-5 has been successfully synthesized from natural zeolite Bayat without further purification. The silica and alumina source are taken from the natural zeolite through submolten depolimerization method. Ludox 40% was used as additional silica source to reach Si/Al ratio of 32 in the starting gel and tetrapropylammonium hydroxide (TPAOH) was used as a structure directing agent (SDA). Synthesis was carried out hydrothermally with aging and crystallization temperature at 150°C. The as-synthesized zeolite was characterized with XRD, FTIR and SEM-EDX. The XRD patterns of the resulted synthesis showed diffraction peaks at 2θ = 7.9°-8.8° (doublet peaks) and diffraction peaks at 2θ = 22°-25° (triplet peaks) which are characteristic for ZSM-5 structure. The SEM image showed that the ZSM-5 zeolite from Bayat natural zeolite had morphology of hexagonal crystalls with some debris of impurities. The elemental analysis using EDX gave Si/Al molar ratio of 18.5.