Elsevier

Zeolites

Volume 18, Issues 5–6, May–June 1997, Pages 379-386

Low-temperature synthesis and characterization of a stable colloidal TPA-silicalite-1 suspension

https://doi.org/10.1016/S0144-2449(97)81256-0Get rights and content

A stable colloidal suspension of the high-silica zeolite, TPA-silicalite-1, has been synthesized at below approximately 35°C and 1 atmosphere pressure in a precipitated silica-TPAOH solution aged for 40 months, as confirmed by small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM), and electron diffraction. Condensation of the aged, TPA-silicalite-1 sol by concentration, followed by purification, drying, and calcinination, yielded a clear (in bulk), glassy silicalite-1 ceramic-like material, stable in air below ca. 800°C. Thus, nucleation and growth of TPA-silicalite-1 is demonstrated for the first time at relatively low temperatures (<35°C), consistent with predictions of crystallization times based upon the kinetic equations of nucleation and crystallization reported in the literature. TEM, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), infrared spectroscopy (i.r.) and nitrogen adsorption isotherms (BET; t-plot) were also used to further characterize the purified and unpurified condensed forms of the aged sol. At this relatively low temperature, precipitated silica probably entered the solution via slow depolymerization. Once available, dissolved silica was templated by the TPA+/H2O structure to yield 5–10-nm germ nuclei, most of which fused syntaxially with other nuclei; the remainder, if any, grew via a surface-limited reaction (in addition to fusion) to give ca. 55-nm diameter single-crystal colloidal TPA-silicalite-1 particles. The ca. 55-nm particles formed are roughly isometric, stabilized in solution by glassy surfaces rich in hydroxyl groups, and have an interfacial area indicative of much smaller constituent subparticles (5–10 nm).

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