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Abstract
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In this work, a facile template-free method, called two-step addition of alkali (TAA method) is developed for the synthesis of ZSM-5 with high crystallinity and well-defined particle morphology. In such method, the total alkali (NaOH) was divided into two parts (i.e., two addition combinations), with the one added some time (interval time) before the other part. By this TAA method, the alkalinity of the synthesis mixture in the lowtemperature synthesis step can be optimized, which was proved to be of key importance in producing ZSM-5 with high crystallinity in the absence of any organic structure directing agents (OSDAs) or ZSM-5 seeds. The influence of different synthetic conditions, including the addition combinations, interval time, hydrothermal treatment time, Si/Al ratio and Na/Si ratio, on the crystallinity and structure of ZSM-5s was studied by different techniques. Under the optimal conditions, the relative crystallinity of the typical ZSM-5 sample Z5(60)-54h is up to 128%, among the highest value so far reported for ZSM-5s synthesized in the absence of OSDAs or any ZSM-5 seeds. The ZSM-5 zeolite prepared in this work show enhanced catalytic performance for LDPE cracking compared with the commercial one. The present work is believed to provide a simple approach for the template-free synthesis of ZSM-5s with high crystallinity and further promote their application.
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