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Frontiers of Chemical Science and Engineering

Front. Chem. Sci. Eng.    2019, Vol. 13 Issue (3) : 543-553
Dealumination and desilication for Al-rich HZSM-5 zeolite via steam-alkaline treatment and its application in methanol aromatization
Yuehua Fang, Fan Yang, Xuan He, Xuedong Zhu()
State Key Laboratory of Chemical Engineering, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China
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The hierarchical HZSM-5 was prepared via dealumination and desilication of commercial Al-rich HZSM-5, and characterized by X-ray diffraction, 27Al magic-angle spinning nuclear magnetic resonance, inductively coupled plasma mass spectrometry, scanning electron microscope, transmission electron microscope, N2 adsorption-desorption, NH3 temperature-programmed desorption, performed thermogravimetric and Raman spectrum. The results showed that partial framework of HZSM-5 was removed after steam treatment at 0.15 MPa, 500°C for 3 h. HZSM-5 with high specific surface area and much mesoporosity was obtained by the subsequent alkaline treatment. The regulation of acid quantity was achieved by altering the concentration of alkaline. Dealumination and desilication of Al-rich HZSM-5 zeolites became more effective using a combination of steam and alkaline treatments than using alkaline treatment alone. Methanol aromatization reaction was employed to evaluate the catalytic performance of treated HZSM-5 at 0.15 MPa, 450°C and MHSV of 1.5 h−1. The results indicated that after steam treatment, HZSM-5 further treated with 0.2 mol/L NaOH exhibits the best catalytic performance: the selectivity of aromatics reached 42.1% and the lifetime of catalyst attained 212 h, which are much better than untreated HZSM-5.

Keywords steam treatment      alkaline treatment      hierarchical ZSM-5      methanol aromatization     
Corresponding Authors: Xuedong Zhu   
Online First Date: 25 February 2019    Issue Date: 22 August 2019
 Cite this article:   
Yuehua Fang,Fan Yang,Xuan He, et al. Dealumination and desilication for Al-rich HZSM-5 zeolite via steam-alkaline treatment and its application in methanol aromatization[J]. Front. Chem. Sci. Eng., 2019, 13(3): 543-553.
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Yuehua Fang
Fan Yang
Xuan He
Xuedong Zhu
Fig.1  XRD patterns of HZSM-5 samples with different treatments
Catalysts AlIV/%a) AlVI/%a) AlIV/AlVI
Z 93.3 6.7 14.0
SZ 86.8 13.2 6.6
SAZ0.2 82.2 17.8 4.6
AZ0.2 88.7 11.3 7.8
Tab.1  Relative amount of Al species in HZSM-5 samples with different treatments
Fig.2  27Al MAS NMR spectra of HZSM-5 samples with different treatments
Catalysts Si/Ala) Relative crystallinity SBETb) /(m2·g?1) Smesoc)/(m2·g?1) Vtotald) /(cm3·g?1) Vmicroc) /(cm3·g?1) Vmeso /(cm3·g?1)
Z 22.2 100 278 54 0.22 0.12 0.1
SZ 22 94.6 325 198 0.23 0.07 0.16
SAZ0.1 24.1 88.2 340 173 0.24 0.08 0.16
SAZ0.2 23.2 69.1 398 196 0.39 0.1 0.29
SAZ0.3 18.2 45.8 445 225 0.66 0.1 0.59
AZ0.2 18.7 77 351 120 0.37 0.12 0.25
Tab.2  Composition, relative crystallinity and physical properties of HZSM-5 samples with different treatments
Fig.3  SEM images of (a) Z, (b) SZ, (c) SAZ0.2, (d) SAZ0.3, and (e) AZ0.2
Fig.4  TEM images of (a) Z, and (b) SAZ0.2
Fig.5  N2 adsorption and desorption isotherms of (a) Z, (b) SZ, (c) SAZ0.1, (d) AZ0.2, (e) SAZ0.2, and (f) SAZ0.3
Fig.6  Pore size distributions of (a) Z, (b) SZ, (c) SAZ0.1, (d) AZ0.2, (e) SAZ0.2, and (f) SAZ0.3
Catalysts Weak acid sitesa) Strong acid sitesa) Total acid sitesa)
Z 0.25 0.33 0.58
SZ 0.11 0.15 0.27
SAZ0.1 0.11 0.17 0.29
SAZ0.2 0.18 0.17 0.36
SAZ0.3 0.28 0.22 0.50
AZ0.2 0.32 0.41 0.73
Tab.3  Acidic properties of ZSM-5 samples with different treatments (unit: mmol?g?1)
Fig.7  NH3-TPD profiles of (a) Z, (b) SZ, (c) SAZ0.1, (d) SAZ0.2, (e) SAZ0.3, and (f) AZ0.2
Catalysts Conversion /% Selectivity /%
M O P C5+ BTX Aromatics
Z 100 4.1 14.2 28.5 9.1 33.6 42.2
SZ 100 1.0 16.4 31.1 19.2 19.8 32.1
SAZ0.1 100 1.3 15.6 28 16.6 28.3 34.6
SAZ0.2 100 1.23 11.8 26.3 17.9 33.5 42.1
SAZ0.3 100 1.6 15 24.8 20 26.9 37.8
AZ0.2 100 3.5 14.4 25 14 33.9 43.2
Tab.4  Products distribution of MTA reaction over different catalystsa)
Fig.8  (a) Methanol conversion and (b) selectivity of aromatics versus time
Fig.9  TG profiles of the deactivated catalysts
Catalysts IvC-H ID1 ID2 ID3 IG ID1/IG Laa)
Z 0.05 0.18 0.22 0.08 0.48 0.37 11.8
SAZ0.2 0.16 0.25 0.17 0.15 0.27 0.93 4.7
SAZ0.3 0.21 0.22 0.15 0.05 0.37 0.60 7.4
AZ0.2 0.19 0.13 0.14 0.14 0.41 0.31 14.4
Tab.5  Raman spectrometry data of the deactivated catalysts
Fig.10  Raman spectra of the deactivated (a) Z, (b) SAZ0.2, (c) SAZ0.3, and (d) AZ0.2
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