Structural information derived from template decomposition in new types of zeolites

The crystallization of Ga-ZSM-5 zeolites and the incorporation of gallium into the framework were investigated by means of TG-DTA measurements. Special attention was paid to the decomposition of the embedded template, which was followed by the observation of coke formed in particular on the external surface of the crystals. A semiquantitative relation was found between the maximum temperature of template decomposition and the Si/Ga ratio in the framework. The amount of embedded template depended on both the zeolite content of the sample and the Si/Ga ratio in the framework. The apparent velocity of desorption of products resulting from the decomposed template, and the coke/template ratio, were sensitive to the crystallinity of the Ga-ZSM-5 samples.