Structure Of ZSM-12 Research Articles

Catalytic conversion of glucose in fructose utilizing high-silica zeolite Sn-ZSM-12

Abstract Tin incorporation in high-silica ZSM-12 zeolite was evaluated using different concentrations of tin and different structure-directing agents (SDA), in order to be used in the glucose isomerization reaction in fructose. The tetraethylammonium hydroxide SDA successfully formed the structure of the high silica zeolite ZSM-12; however, in this system, the addition of Sn prevented the formation of the ZSM-12 zeolite. Therefore, tetraethylammonium bromide was used as SDA, but the syntheses of high-silica ZSM-12 zeolite without and with tin incorporation were not effective. Then methyltriethylammonium chloride was used as SDA, and the high-silica ZSM-12 structure was formed only with the incorporation of tin. The samples with ZSM-12 structure and different concentrations of tin were evaluated in reaction of glucose conversion to fructose. It was found that the sample with the lowest tin content ( Sn / Si = 0 . 005 ) achieved the highest glucose conversion and the highest fructose yield.

Synthesis of ZSM-12 Zeolites with New Templates Based on Salts of Ethanolamines

New class of templates, ethanolamine salts, was used to synthesize zeolites with the ZSM-12 structure. The materials obtained were characterized by methods of powder X-ray diffraction, scanning electron microscopy, IR spectroscopy, low-temperature adsorption–desorption of nitrogen, and elemental analysis. It was shown that, with these templates, it is possible to obtain crystallites with well formed acicular shape, hexagonal morphology, large surface area, and narrow pore size distribution.

Catalytic cracking of isopropylbenzene over hybrid HZSM-12/M41S (M41S = MCM-41 or MCM-48) micro-mesoporous materials

ABSTRACTThe catalytic cracking of isopropylbenzene was investigaded over hybrid ZSM-12/MCM-41 and HZSM-12/MCM-48 micro-mesoporous materials, in order to verify the effect of the acid site of the accessibility of mesoporous channels combined with the acid sites into the zeolite. The hybrid materials were synthesized by the hydrothermal method using the template mechanism. The obtained materials were characterized by X-ray diffraction and BET isotherms using nitrogen adsorption-desorption at 77 K. The X-ray diffraction patterns presented characteristic peaks of the microporous and mesoporous phases. These analysis revealed the formation of ordered hexagonal MCM-41 or cubic MCM-48 mesoporous phases, associated with the ZSM-12 structure. In order to generate acid sites, the materials were ion exchanged with ammonium chloride solution. The calcined hybrid materials were tested as catalyst for cracking of isopropyl-benzene, using a fixed bed reactor at 450 oC and nitrogen gas. The catalytic tests showed that the HZSM-12/AlMCM-41 and HZSM-12/MCM-48 hybrid materials have potential for use in cracking reactions, bening more active than the zeolite or the M41S alone. The catalytic activities of the hybrid materials can be associated with a synergistic effect between the acid sites present on the zeolitic phase and the mesoporous phase. In order to verify how the structure of the hybrid materials may affect and control their catalytic performances, the results were compared with HZSM-12 physically mixed with MCM-41 and MCM-48.

Diasteroselective Structure Directing Effect of (1S,2S)-2-Hydroxymethyl-1-benzyl-1-methylpyrrolidinium in the Synthesis of ZSM-12

The chiral cation (1S,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (bmpm) and a 50% mixture of this with its diastereoisomer (1R,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium have been prepared and tested as structure directing agents (SDAs) in the synthesis of pure-silica zeolites in fluoride medium. The S,S isomer has been shown to efficiently direct the crystallization of zeolite ZSM-12 (MTW); in contrast, the use of a mixture of the two diastereoisomers as a SDA does not lead to the formation of the ZSM-12 structure under the same synthesis conditions, thus suggesting a lower efficiency of the R,S isomer to direct the crystallization of the structure. A computational study based on molecular mechanic simulations allowed explanation of the efficient structure directing role of the S,S isomer in terms of a high host−guest interaction due to a strong structural relationship between the MTW topology and the molecular geometry of the S,S isomer. However, the simulations revealed that the interac...

Crystal structure of pure-silica ZSM-12 with tetraethylammonium cations from X-ray powder diffraction data

Pure-silica ZSM-12, containing tetraethylammonium cations (TEA) was synthesized using a ‘two-silica’ source strategy and its structure was determined from laboratory X-ray powder diffraction data. This is the first known zeolite structure in which the positions of the TEA cations have been established. The ordered arrangement of TEA cations in the straight nonintersecting channels of the host material, which is reflected in several weak superstructural diffraction peaks, was determined by using the combination of simulated annealing and Rietveld refinement. In accordance with Raman spectroscopy, the calculations confirmed the presence of a tt. tt form of the TEA cations and the absence of the other stable form ( tg. tg) which was also consistent with the dimensions and elliptical cross-section of the channels. Therefore in ZSM-12 structure pore (channels) geometry is directly connected with the conformation of TEA cations. The compound with a moiety formula C 16H 40N 2O 84Si 42 ( M r = 2784.28, Z = 4) crystallizes in the monoclinic Cc space group with unit cell parameters a = 25.2177(9), b = 15.1903(5), c = 24.4754(7) Å, β = 108.516(2)°. The final structure, which resulted in a good agreement between calculated and observed powder diffraction pattern ( R wp = 10.17%), was additionally confirmed by results from thermogravimetric measurements and FTIR spectroscopy.

High-Resolution Electron Microscopy Study of ZSM-12 (MTW)

The effect of different structure-directing agents (SDAs) on the nucleation of MTW (the structure code for ZSM-12 recommended by the International Zeolite Association Structure Commission) is shown by means of transmission electron microscopy (TEM). A loose-fit SDA interacting only weakly with the framework seems to have pore-filling character only and results in large domains with rather perfect ZSM-12 framework structure. Conversely, a more tight-fit SDA interacts markedly with the framework during the crystallization and causes simultaneous growth of small domains as well as frequent twinning. By comparison of simulated and experimental electron diffraction patterns as well as high-resolution transmission electron microscopy (HRTEM) images, the proposed crystal structure of ZSM-12 is substantiated. The presence of an organic SDA confined in the one-dimensional channels is established in HRTEM images obtained from calcined as well as as-synthesized specimens. This result is corroborated not only by corr...

Vanadium-Modified Zeolite with the Structure of ZSM-12: EPR and NMR Studies

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTVanadium-Modified Zeolite with the Structure of ZSM-12: EPR and NMR StudiesIgor L. Moudrakovski, Abdelhamid Sayari, Christopher I. Ratcliffe, John A. Ripmeester, and Keith F. PrestonCite this: J. Phys. Chem. 1994, 98, 42, 10895–10900Publication Date (Print):October 1, 1994Publication History Published online1 May 2002Published inissue 1 October 1994https://doi.org/10.1021/j100093a035RIGHTS & PERMISSIONSArticle Views334Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (740 KB) Get e-Alerts

VS-12: a novel large-pore vanadium silicate with ZSM-12 structure

A new large-pore vanadium silicate with ZSM-12 structure has ben synthesized; ESR and NMR data indicate that the vanadium is located in the zeolite framework.

Synthesis of gallosilicates — MTW- type structure zeolites: Evidence of Ga-substituted T atoms

Gallosilicates with the ZSM-12 structure have been synthesized from the reaction mixture of sodium silicate, gallium nitrate, and methyl triethylammonium bromide at 353 K in an autoclave. XRD results associated with an i.r. study of the lattice vibrations indicated that highly crystalline materials with the ZSM-12 structure were obtained. 71Ga MAS n.m.r. studies along with 29Si measurements showed that Ga is in tetrahedral positions and the Si/Ga atomic ratio = 70. T.p.d. of ammonia adsorbed on H-GaZSM-12 clearly showed the acid nature of the material, which supports strongly the presence of Ga 3+ in the zeolite framework.

The combination of synchrotron powder diffraction and high-resolution solid-state NMR experiments

Structural investigations on three zeolites, ZSM-11, ZSM-12 and ZSM-5, have been carried out by a combination of high-resolution solid-state 29Si NMR experiments and Rietveld refinement of synchrotron X-ray powder data. These techniques, being sensitive to short- and long-range order, respectively, gave a most complete picture of the structure of the solid state. Variable temperature NMR experiments of ZSM-11 revealed a displacive phase transition with a change in symmetry at about 300 K. A Rietveld refinement of a data set recorded at 373 K confirmed the proposed structure model. The structure of ZSM-12 was refined from room temperature synchrotron powder data. Space group ambiguities because of psuedo-symmetry of the silica framework of the zeolite were resolved with the aid of 29Si NMR experiments leading to C2/ c as the true space group symmetry. 29Si NMR and X-ray studies of ZSM-5 showed that the symmetry of the crystal structure depends on the temperature, the concentration of the guest molecule, and on the number of Al atoms in the framework. A full pattern refinement of silica-ZSM-5 loaded with two molecules p-dichlorobenzene per unit cell showed that the site occupied by the sorbed molecule is not at the intersection of the channels but shifted by 1 4 along b 0.

Crystal structure of silica-ZSM-12 by the combined use of hgh-resolution solid-state MAS NMR spectroscopy and synchrotron x-ray powder diffraction

The crystal structure of the synthetic zeolite silica-ZSM-12, 56 SiO{sub 2}, has been solved by the combined use of high-resolution solid-state MAS NMR spectroscopy and high-resolution synchrotron X-ray powder diffraction ZSM-12 crystallizes in the monoclinic space group C2/c with a{sub 0} = 24.863 {angstrom}, b{sub 0} = 5.012 {angstrom}, c{sub 0} = 24.328 {angstrom}, and {beta} = 107.7{degree}. The zeolite host structure is built from corner-linked SiO{sub 4} tetrahedra to give a three-dimensional 4-connected net. The pores of the structure are one-dimensional channels that do not intersect, with 12-membered ring pore openings of approximately 5.6 {times} 7.7 {angstrom}. The structure of ZSM-12 is frequently twinned with (100) as the twin plane, which indicates a new zeolite structure type.

The framework topology of ZSM-12: A high-silica zeolite

The framework structure of ZSM-12, a high-silica zeolite, was determined by analysis of electron and X-ray powder diffraction data combined with model building. The monoclinic ceil parameters of ZSM-12 ( Si Al -ratio = 310) are a = 24.88 ± 0.04Å, b = 5.02 ± 0.02Å, c = 12.15 ± 0.03Å, and β = 107.7 ± 0.1°. The ideal framework symmetry is C2/m with 28 T-atoms per unit cell. The calculated density (SiO 2 end-member) is 1.93 g cm −3. The structure contains elements of the ab-projection of ferrierite linked via 4-rings to produce a net with 12-rings. The bc-projection is a 6-ring net. The 12-ring channels (5.7 × 6.1 Å) are linear and noninterpenetrating.