Local Structures of Two-Dimensional Zeolites—Mordenite and ZSM-5—Probed by Multinuclear NMR

Abstract

Mesostructured pillared zeolite materials in the form of lamellar phases with a crystal structure of mordenite (MOR) and ZSM-5 (MFI) were grown using CTAB as an agent that creates mesopores, in a one-pot synthesis; then into the CTAB layers separating the 2D zeolite plates were introduced by diffusion the TEOS molecules which were further hydrolyzed, and finally the material was annealed to remove the organic phase, leaving the 2D zeolite plates separated by pillars of silicon dioxide. To monitor the successive structural changes and the state of the atoms of the zeolite framework and organic compounds at all the steps of the synthesis of pillared MOR and MFI zeolites, the nuclear magnetic resonance method (NMR) with magic angle spinning (MAS) was applied. The ²⁷Al and ²⁹Si MAS NMR spectra confirm the regularity of the zeolite frameworks of the as synthetized materials. Analysis of the ¹H and ¹³C MAS NMR spectra and an experiment with variable contact time evidence a strong interaction between the charged “heads” –[N(CH ₃) ₃] ⁺ of CTAB and the zeolite framework at the place of [AlO ₄] ⁻ location. According to ²⁷Al and ²⁹Si MAS NMR the evacuation of organic cations leads to a partial but not critical collapse of the local zeolite structure.