IDENTIFICATION OF DIFFERENT TETRAPROPYLAMMONIUM CATIONS OCCLUDED IN ZSM-5 ZEOLITE BY COMBINED THERMAL-ANALYSIS (TG-DTA) AND C-13-NMR SPECTROSCOPY

The combined use of thermal analysis (t. g. -d. t. a. ) and **1**3C-n. m. r. spectroscopy allows one to identify four different structural environments for TPA** plus ions occluded in the ZSM-5 channels. A first low-temperature (ca. 380 degree C) d. t. a. peak is assigned to less strongly held or outer shell 'strained' TPA** plus ions (type I), while a large intermediate temperature (ca. 425 degree C) peak C1 is attributed to inner-strained TPA** plus ions (type II). Both TPA** plus species neutralize the SiO** minus defect groups. The high-temperature (ca. 475 degree C) peak is attributed to two different TPA** plus ions: those neutralizing the framework (Si-O-Al)** minus negative centers (type III) (for high Al content samples), and those in the relaxed form that also neutralize SiO** plus defect groups (type IV) (for both high- and low-Al-content samples). Types I-III all show the same **1**3C-n. m. r. spectra (splitting of the CH//3-n. m. r. line), while type IV exhibits only one n. m. r. line for the CH//3// minus groups.