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Abstract
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A new composite zeolite, ZSM-5/Beta, was developed by incorporating Beta zeolite into the synthesis gel of ZSM- 5 zeolite. Beta and ZSM-5 zeolite have been prepared from rice husk ash without using an organic template. First, the effect of synthesis temperature and seeding agent on structural properties of Beta zeolite was investigated. Then, prepared Beta zeolite was added to the ZSM-5 structure with the hydrothermal method. The prepared samples were characterized by X-ray diffraction, ield emission scanning electron microscopy, N2 physical adsorption, and temperature-programmed ammonia desorption techniques. Results indicated that the synthesis at a temperature of 150 ◦ C and using Na-Beta seeds showed suitable crystallinity as well as textural properties. Furthermore, the crystalline structure of ZSM-5 wasn’t damaged by the addition of Beta zeolite. The incorpo-ration of Beta zeolite into the ZSM-5 structure increased the total pore volume by 45%. The micropore volume and the mesopore volume also increased by 2% and 300%, respectively. Using composite zeolite led to tuning the catalyst acidity. The catalytic activity of this new ZSM-5/Beta composite structure was evaluated in the MTG process at 400 ◦ C, WHSV of 20 h 1 and atmospheric pressure. The results illustrated that over this composite catalyst, the selectivity to alkylated aromatics increased by almost 13% compared to the initial ZSM-5 zeolite. Furthermore, gasoline production yield and catalyst lifetime also increased by 9% and 61% respectively compared to the initial ZSM-5 zeolite. The better performance of the composite zeolite can be ascribed to its higher mesoporous volume and lower acidity. The composite catalyst has a lower number of acid sites, especially the number of strong acid sites that are one of the main factors in coke deposition.
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