Pn. Joshi et al., PHYSICOCHEMICAL CHARACTERIZATION OF THE INTERMEDIATE PHASES OBTAINED DURING THE HYDROTHERMAL CRYSTALLIZATION OF LTL ZEOLITES, Journal of physical chemistry, 99(12), 1995, pp. 4225-4229
The physicochemical changes in the solid phases obtained during the hy
drothermal crystallization of LTL zeolite in pure potassium form at 42
3 K have been reported. Samples of varying crystallinity, obtained at
different crystallization periods, were characterized by different tec
hniques such as XRD, DTA/TG, MAS-NMR, IR, chemical compositions, and t
he sorption data. The significant changes observed in the framework IR
spectra (400-1200 cm(-1)) were found to be helpful in estimating the
progress in the crystallization. The area under the low temperature en
dotherm in DTA was also correlated with percent crystallinity of the s
ample. Except in the lower range, XRD crystallinity was in excellent a
greement with IR crystallinity and with the crystallinity evaluated fr
om the benzene uptake. The crystallinity evaluated from the uptake of
water, n-hexane, cyclohexane, and nitrogen showed nearly sigmoid type
curves indicating the progressive crystallization. Both Si-29 and Al-2
7 MAS-NMR spectra showed the changes in the number of different silico
n environments and existence of all the aluminum species in the ordere
d tetrahedral coordination, respectively. The changes observed in the
chemical composition of the samples of different crystallinity were fo
und to be useful in understanding the crystallization mechanism.