Solvent-free and Mesoporogen-free Synthesis of Mesoporous Aluminosilicate ZSM-5 Zeolites with Superior Catalytic Properties in the Methanol-to-Olefins Reaction

详细信息    查看全文

• 作者：Changsheng Zhang ; Qinming Wu ; Chi Lei ; Shuxiang Pan ; Chaoqun Bian ; Liang Wang ; Xiangju Meng ; Feng-Shou Xiao
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2017
• 出版时间：February 15, 2017
• 年：2017
• 卷：56
• 期：6
• 页码：1450-1460
• 全文大小：841K
• ISSN：1520-5045

文摘

Large crystalline particles of ZSM-5 zeolites (S-ZSM-5) have been successfully synthesized by adjusting crystallization time and Si/Al ratios in the starting solid mixtures in the absence of water solvent. Catalytic tests in the methanol-to-olefins (MTO) reaction show that these S-ZSM-5 zeolites obtained from the solvent-free route exhibit superior catalytic properties including excellent propylene selectivity and extraordinarily long life in the MTO reaction. Particularly, when the crystallization time is 30 h and the Si/Al ratio in the starting solid mixture is adjusted at 150 under the solvent-free conditions, the S-ZSM-5-30h-150 catalyst with the large particle sizes (10–20 μm) gives propylene selectivity as high as 50.0% and catalyst life as long as 9 h, which are much better than those (propylene selectivity at 38.9% and catalyst life of 3 h) of the conventional ZSM-5 zeolite with smaller crystals (ca. 5 μm) synthesized from the hydrothermal route. High-resolution TEM images of these S-ZSM-5 zeolites demonstrate that there is mesoporosity in the samples. More interestingly, these mesopore size distributions could be adjusted by the crystallization time during the solvent-free synthesis. Obviously, the presence of mesoporosity is very favorable for the mass transfer, and an appropriate Si/Al ratio in the zeolite framework could offer suitable acidic density for the catalytic conversion, which should be responsible for the superior catalytic properties in the MTO over the S-ZSM-5-30h-150 catalyst. The features of mesoporosity in the S-ZSM-5 crystals and sustainability for the solvent-free synthesis could be potentially important for wide applications of these S-ZSM-5 zeolites in the future.