The framework topology of ZSM-48: A high silica zeolite

doi:10.1016/0144-2449(85)90124-1

Zeolites

Volume 5, Issue 6, November 1985, Pages 355-358

Zeolites

https://doi.org/10.1016/0144-2449(85)90124-1 Get rights and content

Abstract

ZSM-48 is a high silica zeolite with orthorhombic or pseudoorthorhombic symmetry whose X-ray powder pattern can be indexed on the basis of a Pmma-orthorhombic cell with a = 14.24 ± 0.03Å, b = 20.14 ± 0.04Å, and c =8.40 ± 0.02Å (HZSM-48, $Si Al$ = 580). All reflections inconsistent with both C- and l-centering are quite weak suggesting ideal Cmcm or Imma symmetry.

A disordered structure consisting of ferrierite sheets linked via bridging oxygens located on mirror planes is proposed for this material.

These structures are characterized by ten-ring noninterpenetrating linear channels whose ideal dimensions are 5.3 × 5.6 Å.

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The discovery of Titanium-Silicalite-1 (TS-1), reported in the late 1970s, is a milestone in the science and technology of zeolites. As an oxidation catalyst, TS-1 operates under mild conditions with high activity and selectivity, and it is presently applied in several industrial processes. As a medium-pore zeolite, the small size of the 10-ring pore openings imposes diffusion limitations when working with even relatively large molecules. To overcome this drawback, a thriving line of research was soon undertaken aimed at incorporating Ti into the framework of zeolites with different pore architecture and sizes. In this review, we would like to retrace the fundamental steps of the synthesis of crystalline microporous titanosilicates, highlighting not only the early works but, above all, the most recent advances. The analysis of the literature provides an exhaustive picture of the efforts made by the researchers together with useful indications for developing increasingly selective and efficient catalytic materials.
Quantitatively regulating ZSM-48 by phenolic molecules for n-hexadecane hydroisomerization
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ZSM-48 is widely used to support Pt nanoparticles (Pt/ZSM-48) for hydroisomerization of long-chain n-paraffin due to its 10-member-ring one-dimensional pore structure. But the yield of target isomers on Pt/ZSM-48 is difficult to be improved due to easily bundled crystal bars and relatively excessive acid sites of ZSM-48, which restricts reactant diffusion and causes cracking. In this study, different types of zeolite growth modifiers (ZGMs) are screened for regulating the physicochemical property of ZSM-48, in which phenolic hydroxyl was found to be the most effective functional group. Quantitative correlations between ZGM structure and the properties of corresponding ZSM-48 crystal are achieved based on appropriate descriptors and multi-parameter regression. Then, the mechanism of ZSM-48 regulation by phenolic ZGMs is revealed. The models predict that polydopamine (PDA) is a superior ZGM for hydroisomerization, which is verified by textural characterization and reaction evaluation. Compared with the conventional catalyst, the isomer selectivity was improved effectively from 92% to over 97% when the feed conversion was lower than 80%, and the maximum yield of isomers was 89.0% as catalyzed by the PDA-regulated catalyst. The as-built models can also be used to design preferred phenolic ZGMs for preparing tailored ZSM-48 in other applications.
Suppressing the aromatic cycle of the dimethyl ether to hydrocarbons reaction on zeolites
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The influence of the zeolite framework type on the conversion of dimethyl ether (DME) to hydrocarbons (DTH) was investigated for *MRE, MFI and TON zeolite catalysts. Remarkable differences in the catalytic performance of the materials were observed. In particular, the *MRE zeolite showed an exceptionally high yield of olefins (90%) with a substantial ratio of products in the chain length range C₅-C₁₁. Additionally, the longevity of the *MRE zeolite clearly exceeded previously reported data. The comparison of mechanistic parameters (Hydrogen-Transfer-Index HTI_Ci and C₃/C₂ ratio) demonstrated for this zeolite, that the formation of aromatics in the reaction network can be almost completely suppressed under suitable reaction conditions. By varying the reaction parameters temperature, DME partial pressure and weight hourly space velocity (WHSV), it was possible to identify the optimal combination of selectivity and deactivation resistance for each material. The olefin-rich DTH product of the *MRE zeolite offers manifold possibilities for further conversion to valuable renewably produced low-emission fuels like gasoline or jet fuel.
Beyond TS-1: Background and recent advances in the synthesis of Ti-containing zeolites
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Citation Excerpt :
ZSM-48 is a high-silica zeolite with framework based on ferrierite sheets forming a mono-dimensional 10-ring channels system with free dimensions 5.3 × 5.6 Å, firstly synthesized in pure form using tetramethylammonium chloride and n-propylamine [47] and later with 1,8-diaminooctane as SDAs [48]. Its disorder framework was firstly described by the intergrowth of two polytypes 48A and 48B [49] but this model does not quantitatively account for the features of the X-ray diffraction pattern, which can be better reproduced using nine distinct polytypes [50]. From the catalytic point of view, ZSM-48 is not particularly interesting.
The discovery of Titanium-Silicalite-1 (TS-1), reported in the late 1970s, is a milestone in the science and technology of zeolites. As an oxidation catalyst, TS-1 operates under mild conditions with high activity and selectivity, and it is presently applied in several industrial processes. As a medium-pore zeolite, the small size of the 10-ring pore openings imposes diffusion limitations when working with even relatively large molecules. To overcome this drawback, a thriving line of research was soon undertaken aimed at incorporating Ti into the framework of zeolites with different pore architecture and sizes. In this review, we would like to retrace the fundamental steps of the synthesis of crystalline microporous titanosilicates, highlighting not only the early works but, above all, the most recent advances. The analysis of the literature provides an exhaustive picture of the efforts made by the researchers together with useful indications for developing increasingly selective and efficient catalytic materials.
Fabrication of highly mesoporous ZSM-48 zeolite by anionic surfactant-organosilane system for catalytic conversion of methanol to gasoline
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A highly mesoporous ZSM-48 zeolite has been prepared using low-cost anionic surfactant sodium dodecylsulphate (SDS) as mesopore-generating agent and short-chain 3-aminopropyltrimethoxysilane (APTMS) as co-structure directing agent. The mesoporosity formation took place through the interaction between the silica species/APTMS and SDS molecules existing in the gel composition. In the synthesis solution with a pH slightly less than ten, the methoxysilyl moiety in APTMS was hydrolysed to the –SiO₃ units and became incorporated inside the zeolite crystals while the positively charged ammonium site of APTMS interacted with the negatively charged head group of the SDS. Aggregation of aluminosilicate/APTMS species around the SDS micelles during the crystallization process, led to the formation of a mesoporous zeolite. In this study, a conventional ZSM-48 and seven ZSM-48 zeolites from different mixtures containing SDS, APTMS and SDS-APTMS with different APTMS/SiO₂ molar ratios were synthesized. Changes in the properties of the synthesized samples were investigated by XRD, FTIR, SEM, TEM, nitrogen adsorption/desorption isotherms, NH₃-TPD and TGA. The optimum ZSM-48/Sur/0.008OS zeolite prepared with APTMS/SiO₂ molar ratio of 0.008 exhibited both bundled needle-like and spherical morphologies. The catalytic conversion of methanol to gasoline (MTG) was evaluated in a fixed-bed reactor, and the results revealed that mesoporosity development using Sur-OS system enhanced catalytic activity of ZSM-48/Sur/0.008OS catalyst compared to the other sample. The optimum zeolite showed long stable phase of 40 h and liquid hydrocarbon yield of 42% was achieved for 100% methanol conversion in 22 h of reaction. The proposed method opens a new and simple route for the synthesis of hierarchically porous ZSM-48 with tunable porosity using low-cost anionic surfactants.
Facile and selective approach towards synthesis of a series ZSM-5/ZSM-12 catalysts for methanol to hydrocarbons reactions: Applying different synthesis driving force and conditions
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Citation Excerpt :
The XRD patterns of the synthesized samples in the range of 2θ = 5–30° are shown in Fig. 3. By comparing and matching the diffraction peaks of the synthesized zeolites with the reference XRD patterns reported in the literature [36], it was found that most of the prepared zeolites have two phases ZSM-12 and ZSM-5 in their structure and according to the number and intensity of peaks, the predominant phase is ZSM-5 crystal structure and ZSM-12 phase is less in the zeolite. In XRD diagrams, the relative crystallinity of each sample was calculated using the sum of the intensity of index peaks in the range 2θ = 20–25° on the basis of the optimal sample.
The use of ultrasonic waves was developed for synthesis of zeolites at shorter crystallization time with improving their desirable properties. A series of nanostructured ZSM-5/ZSM-12 composite zeolites with different Si/Al ratios and alkalinity using organic templates were prepared by hydrothermal and sonochemical synthesis methods. The physicochemical properties of synthesized nanocatalysts such as structure, morphology, textural, and acidity were characterized via XRD, FESEM, N₂ physisorption, FTIR, TPD-NH₃, TGA-DTG techniques. The results revealed that increasing the Si/Al ratio and alkalinity in the hydrothermal samples enhanced the crystallization, formation of amorphous microcrystals, and dominant phase of MFI with decreasing MTW competitive phase. Zeolites synthesized by high-temperature and short-time sonochemical method had higher crystallinity, less dominant phase of ZSM-5, smaller crystals, greater surface areas, higher concentration of Brønsted acid sites, and stronger strength of moderate/strong acid sites. The catalytic performance of the zeolites for MTH conversion was evaluated under a reaction temperature of 450 °C at different times on stream. The results showed that the sonochemical zeolite had a higher methanol conversion (100%), higher selectivity toward olefins (28% vs. 19%) with more C₃⁼/C₂⁼ ratio (0.79 vs. 0.58), and lower alkanes selectivity (66% vs. 72%) after 240 min TOS.

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Short paperThe framework topology of ZSM-48: A high silica zeolite

Abstract

Nature

Acta Crystallogr.

Min. Mag.

A Revised Program for Calculating X-Ray Powder Diffraction Patterns

Short paper
The framework topology of ZSM-48: A high silica zeolite