Acta Phys. -Chim. Sin. ›› 2002, Vol. 18 ›› Issue (09): 786-790.doi: 10.3866/PKU.WHXB20020904

• ARTICLE • Previous Articles     Next Articles

Dealumination of HZSM-5 Zeolite by Calcination:27Al Multiple Quantum MAS NMR Study

Chen Lei;Deng Feng;Ye Chao-Hui   

  1. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071
  • Received:2002-01-02 Revised:2002-03-25 Published:2002-09-15
  • Contact: Deng Feng

Abstract: The coordination states of aluminum species in calcined HZSM-5 zeolites have been investigated using 29Si, 27Al MAS and 2D MQMAS NMR methods. A broad peak at δ 45 in presents in the 27Al MAS NMR spectra of calcined HZSM-5 zeolites. From the 27Al 3QMAS NMR spectrum, it is evident that the peak at δ 45 comes mainly from the distorted tetrahedral Al with a quadrupolar-coupling constant of 5.2 MHz. Simulation of the 27Al 1D MAS NMR spectra of samples calcined at 700 and 750 ℃ shows that a small peak at about δ 30 emerges, which is probably due to 5- coordinated non-framework Al. The existence of this Al species is also confirmed by 27Al 3QMAS NMR.HZSM-5 zeolite calcined at temperature higher than 700 ℃ suffers severe dealumination. Calcination causes part of the Al species “NMR invisible” in the corresponding 27Al MAS spectra.

Key words: HZSM-5, NMR, MQMAS, Dealumination, Calcination