100 research outputs found

    Synthesis of the Ti-Silicate Form of BEC Polymorph of B-Zeolite Assisted by Molecular Modeling

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    This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/jp805400u Published Work, see http://pubs.acs.org/page/policy/articlesonrequest/index.html[EN] The K(+) free pure silica form of polymorph C (BEC) of beta-zeolite has been synthesized with a cationic organic structure directing agent (SDA) that was predicted best, out of a series of nine potentials, by means of modeling techniques. On the bases of this synthesis method, the Ti-BEC zeolite has been obtained which owing to the pore topology and dimensions shows a higher epoxidation activity than the Ti-beta-polymorph either with H(2)O(2) or organic peroxides as oxidants.The authors thank the CICYT for financial support (Project MAT 2006-14274-CO2-01). G.S. thanks "Centro de Calculo de la Universidad Politecnica de Valencia" for the use of their computational facilities. M.M. and P.S. thank ITQ for a scholarship. We also thank intramural project CRENATUM.Moliner Marin, M.; Serna Merino, PM.; Cantin Sanz, A.; Sastre Navarro, GI.; Díaz Cabañas, MJ.; Corma Canós, A. (2008). Synthesis of the Ti-Silicate Form of BEC Polymorph of B-Zeolite Assisted by Molecular Modeling. The Journal of Physical Chemistry C. 112(49):19547-19554. https://doi.org/10.1021/jp805400uS19547195541124

    Investigation on the porosity of zeolite NU-88 by means of positron annihilation lifetime spectroscopy

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    Seven well characterized zeolites were investigated by positron annihilation lifetime spectroscopy. The lifetime spectra were analysed in four discrete components. The third one was associated with ortho-positronium annihilation in the channels, framed in terms of infinite cylinders. Differences between the radii determined from the positron annihilation technique and X-ray diffraction data were found and explained in terms of the physical structure of the channel. An analogous study on a high-silica NU-88 zeolite gave a value of 0.33 nm for the corresponding radius, in agreement with At and N(2) adsorption data as well as with the catalytic behaviour of this zeolite in several acid catalyzed reactions. The longest lifetime component in NU-88 reveals the existence of mesopores, with average radius of about 1.8 nm, which could explain the importance of hydrogen transfer reactions in this zeolite

    Synthesis and comparative characterization of Al, B, Ga, and Fe containing Nu-1-type zeolitic framework

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    We synthesized four different Nu-1-type zeolites containing, respectively, Al, B, Ga, and Fe as the trivalent element. With the exception of B-Nu-1, the synthesis is difficult because of the competitive formation of other crystalline phases as sodalite, ZSM-39-type, or glassy phases. The trivalent elements isomorphous substitution was demonstrated by X-ray powder diffraction, FTi.r., e.s.r., u.v.-Vis., and 27Al, 11B, and 71Ga-MAS-n.m.r. By the same techniques and t.g.a. measurements, we evaluated the thermal stability of the different Nu-1-type zeolites

    B-containing molecular sieves crystallized in the presence of ethylenediamine. Part II: crystal structure of as-synthesized B-MFI.

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    Hydrothermal treatment of an aqueous solution containing tetramethoxysilane, boric acid and ethylenediamine (EN) led to the crystallization of B-MFI (BOR-C) together with small amounts of B-ferrierite. A single-crystal X-ray diffraction study was performed on two small prismatic crystals of BOR-C with the unit cell dimensions: a = 19:869, b = 19:661, c = 13:207A, V = 5159A3, and a = 19:875, b = 19:669, c = 13:218A, V = 5167A3 (space group Pnma) using a laboratory diffractometer equipped with a CCD detector and a synchrotron radiation source, respectively. In both cases the unit cell volume and the B/Si occupancy agree with about 15% substitution of B for Si in the framework T-sites, corresponding to 14 B/u.c. Three independent EN molecules were located, one (EN1) is located in the sinusoidal 10-ring channel parallel to the [100] direction, lying on the (010) plane, the other two (EN2 and EN3) in the straight 10-ring channel. The negative charge of the framework is counterbalanced by the EN molecules in the form of divalent cations
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