Multinuclear MAS NMR spectroscopic study of the zeolite, MCM-22

Abstract

The sodium form of the novel silica-rich zeolite MCM-22 of moderate Si/Al ratio (44) has been synthesized hydrothermally and studied by multinuclear (¹H, ²⁷Al and ²⁹Si) magic-angle spinning (MAS) NMR spectroscopy. ²⁷Al spectra indicate that, in the as-synthesized (CN) and calcined materials, all the aluminium atoms are in the tetrahedral framework positions. The silicon resonance at δ=– 105.1 in the calcined material is found to correspond to Q⁴(1Al) and tetrahedral-sites (T-sites), T₂+ T₆[Q⁴(0AI)] of the orthorhombic structure. Silanol, Q⁴(1Al) and cryst allographically non-equivalent Q⁴(0Al) lattice sites are identified and information has been gathered on the interaction between the template protons and the lattice T-sites through ¹H–²⁹Si cross-polarization dynamics experiments. Our results also indicate that in the as-synthesized material, the ²⁹Si resonances at δ=– 104.3 and – 120.9 correspond to distant T-sites that are located away from the template molecules in the zeolite pores.