(653b) 3D-Printed Monoliths of MFI Zeolite with Hierarchical Porosity for Methanol-to-Olefin Reaction

Authors: 
Li, X., Missouri University of Science and Technolgoy
Rownaghi, A., Missouri University of Science and Technology
Rezaei, F., Missouri University of Science and Technology
Abstract

Previous works have shown that the 3D-printing zeolite are promising for the application of adsorption and catalysis.1, 2 Herein, we report the rapid synthesis of customized zeolite monoliths with various compositions and hierarchical porosity (macro-meso-micro) using 3D printing technique. Moreover several 3D-printed monoliths were synthesized from HZSM-5 and HZSM-5/silica, SAPO-34 crystals were grown on as-synthesized 3D-printed ZSM-5 monoliths via secondary growth method. The 3D-printed zeolite monoliths exhibited hierarchical porosity with pore sizes ranging from 1.5 nm to 1 µm. Characterization results suggested that the formulation into the monolith structure enhanced mesopore volume and moderated the acidity of the structures. Further incorporation of amorphous silica into the HZSM-5 monoliths reduced the acid sites density. The obtained monoliths were evaluated in methanol to olefins (MTO) reaction and found to exhibit higher stability than their powder counterparts. The selectivity to light olefins was significantly increased as a result of modification in acidity and porosity of the monolith catalysts, which in turn mitigated the hydrogen transfer, hence suppressing the formation of paraffin and aromatics. SAPO-34 coating tended to increase the ethylene selectivity due to its intrinsic framework structure. Analysis of spent zeolite monoliths by TGA-DTA indicated that the amount of polyaromatic species formed during the reaction was much less than that on the powder analogues, due to their diluted acid site density and decreased Brønsted acid sites, as proven by NH3-TPD profiles and py-FTIR spectra. Furthermore, 29Si MAS NMR results confirmed slight dealumination of 3D-printed monoliths after MTO reaction.

References

  1. Thakkar, H.; Eastman, S.; Hajari, A.; Rownaghi, A. A.; Knox, J. C.; Rezaei, F., 3D-Printed Zeolite Monoliths for CO2 Removal from Enclosed Environments. ACS Applied Materials & Interfaces 2016, 8, (41), 27753-27761.
  2. Li, X.; Li, W.; Rezaei, F.; Rownaghi, A., Catalytic cracking of n-hexane for producing light olefins on 3D-printed monoliths of MFI and FAU zeolites. Chemical Engineering Journal 2018, 333, (Supplement C), 545-553.
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