Synthesis and characterization of MCM-22 in fluoride media.

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–bAl(OH)3–30SiO2–15HMI–1350H2O with M=NH4, Na, K or Cs; HMI=hexamethyleneimine ; 20≤a≤40 and 0.5≤b≤4. The increase of Si/Al in the initial 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 characterized by X-ray diffraction, proton-induced γ-ray emission, thermal analysis and multi-nuclear NMR techniques.

Most samples were obtained in a pure form, where the aluminum atoms are incorporated in the tetrahedral sites of the MCM-22 structure. Several tetrahedral aluminum species could be identified by 27Al NMR. The 29Si NMR spectra showed some seven different lines. The 13C NMR spectra were characteristic of two different HMI molecules incorporated intact in the porous volume. Apart from the reaction rates and the crystal morphology, the characteristics of the MCM-22 samples are similar to those obtained in alkaline media only.