HZSM-5 zeolites undergoing the high-temperature process for boosting the bimolecular reaction in n-heptane catalytic cracking

High -temperature treatment is key to the preparation of zeolite catalysts. Herein, the effects of hightemperature treatment on the property and performance of HZSM-5 zeolites were studied in this work. X -Ray diffraction, N2 physisorption, 27Al magic angle spinning nuclear magnetic resonance (MAS NMR), and temperature -programmed desorption of ammonia results indicated that the hightemperature treatment at 650 degrees C hardly affected the inherent crystal and texture of HZSM-5 zeolites but facilitated the conversion of framework Al to extra -framework Al, reducing the acid site and enhancing the acid strength. Moreover, the high -temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking, promoting the conversion and light olefins yield while inhibiting coke formation. Based on the kinetic and mechanism analysis, the improvement of HZSM-5 performance caused by high -temperature treatment has been attributed to the formation of extra -framework Al, which enhanced the acid strength, facilitated the bimolecular reaction, and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking. (c) 2023 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.