Yali Zhang, Kai Zhang, Chao Shang, Xiaoning Wang, Lei Wu, Guoqing Huang, Hao Wang, Qiming Sun, Xiao Dong Chen, Zhangxiong Wu
Abstract
Methanol-to-olefin (MTO) conversion on zeolites has encountered severe coke deposition and rapid deactivation. Creating different levels of porosity is essential to mitigate such issues. Herein, we demonstrate a facile and green strategy to synthesize uniform and hierarchically macro/mesoporous ZSM-5 microspheres by combining spray-freeze drying and steaming-assisted crystallization (SAC). The structure, crystallinity, and porosity of the zeolite microspheres are controlled by adjusting the water/gel mass ratio and time in the SAC process. The structure evolution during the SAC process is revealed. In the catalytic MTO reaction, the representative hierarchically porous ZSM-5 catalyst exhibits superior catalytic performance. At a very high weight hourly space velocity of 18 h−1, it shows a dramatically prolonged lifetime (47 h at >99% conversion) and much-improved selectivity to ethylene and propylene compared with the conventional microporous ZSM-5 and nano-sized ZSM-5. The enhanced performance is originated from the hierarchical structure and suitable acidity of the ZSM-5 microspheres.