Journal
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
Volume 56, Issue 6, Pages 1450-1460Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.iecr.7b00062
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Funding
- National Natural Science Foundation of China [21333009, 21422306, U1462202]
- Fundamental Research Funds for the Central Universities [201SXZZX004-04]
- Zhejiang Provincial Natural Science Foundation of China [LR15B030001]
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Large crystalline particles of ZSM-5 zeolites (S-ZSM-S) have been successfully synthesized by adjusting crystallization time and Si/A1 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/A1 ratio in the starting solid mixture is adjusted at 150 under the solvent-free conditions, the S-ZSM-5-30h-LS0 catalyst with the large particle sizes (10-20 mu m) 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 mu m) synthesized from the hydrothermal route. High-resolution TEM images of these S-ZSM-S 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/A1 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.
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