Synthesis and characterization of aluminosilicate MCM-22 in basic media inthe presence of fluoride salts

MCM-22 zeolite was prepared using NaF and KF as mineralizing agents with an Si/Al ratio ranging from 15 to 30, The initial batch composition was aMF-b Al(OH)(3)-30SiO(2)-15HMI-1350H(2)O with M=NH4, Na, K or Cs; HMI = hexamethy leneimine; 20 less than or equal to a less than or equal to 40 and 0.5 less than or equal to b less than or equal to 4. The increase of Si/Al in the i nitial mixture determines the crystallization of ZSM-51 and ZSM-35 zeolite type structures. However, the presence of NH4F and CsF did not promote the crystallization of any type of zeolite structure. MCM-22 zeolite was charac terized by X-ray diffraction, proton-induced gamma-ray emission, thermal an alysis and multi-nuclear NMR techniques, Most samples were obtained in a pure form, where the aluminum atoms are inc orporated in the tetrahedral sites of the MCM-22 structure. Several tetrahe dral aluminum species could be identified by Al-27 NMR. The Si-29 NMR spect ra showed some seven different lines. The C-13 NMR spectra were characteris tic of two different HMI molecules incorporated intact in the porous volume . Apart from the reaction rates and the crystal morphology, the characteris tics of the MCM-22 samples are similar to those obtained in alkaline media only. (C) 2000 Elsevier Science B.V. All rights reserved.