Preparation of high-silica faujasites by treatment with silicon tetrachloride

Abstract

NaY has been dealuminated in highly controlled conditions by SiC1,. The materials thus obtained, after subsequent washing and ammonium exchange, were characterized by chemical analysis, thermogravimetry, X-ray diffraction, infrared spectroscopy of the framework and surface hydroxyl groups and 29Si nuclear magnetic resonance spectroscopy.In order to obtain highly crystalline materials in a reproducible way, a very specific dealumination and washing procedure has to be followed. The mechanism of the dealumination is complex and always combines direct isomorphic substitution with acid leaching of aluminium. The materials obtained have continuously varying properties as far as unit-cell dimensions and framework vibrations are concerned. In contrast, the amount of extra-lattice aluminium retained in the zeolite reaches a maximum at intermediate degrees of dealumination.

Characterization of Zeolites — Infrared and Nuclear Magnetic Resonance Spectroscopy and X-Ray Diffraction

“…In fact, such relations were later on frequentlyused to determine the Al! (Si + AI) ratio in zeolite frameworks (compare, e.g., [39,40]). The T -0 bending band did not vary significantly, in particular not with the same structure and different Si/ Al ratios.…”

“…4.59 to 4.62 and, hence, of the method described in this section is first of all due to the error made in the distinction between framework and extra-framework aluminum. It is known, that Y zeolite partially dealuminated with SiCl 4 [462] or by ultrastabilization and extraction methods [459] contains considerable amounts of extra-framework aluminum species. Thus, coefficients obtained from experimental data of dealuminated Y zeolite samples in the range Nal < 50, except if NaJ = 0, may be less reliable.…”

Introduction of gallium in HZSM5 and HY zeolites by post-synthesis treatment with trimethylgallium

“…Also for this zeolite, no changes in crystallinity were observed in the XRD spectra after the subsequent treatments. A peak at about 930 cm-1 was observed earlier in SiC14/HC1 dealuminated HY samples and has been attributed to asymmetric bending vibrations of the bridged Si-OH groups, originating from silanol nests [3,4,20,22,23].…”

“…A well known example in this field is the dealumination of aluminosilicates with SiC14 or (NH4)2SiF6, replacing Si for A1 in the zeolite framework [3][4][5]. Another example is the preparation of titanium silicalite (TS-1) via an indirect method using TiC14 vapour, as described by Kraushaar and Van Hooff [6].…”

Characterization of basic guest compounds on solid catalysts by13C CP/MAS NMR spectroscopy of surface methoxy groups

“…Dealuminated zeolite USY was prepared according the method described by Beyer et al 22 by treating zeolite NaY with SiCl 4 up to n Si /n Al ³ 950. Silica gel was purchased from Fluka (Buchs, Switzerland) (980911).…”