NMR applied to zeolite synthesis

Zeolites are synthesized from highly alkaline aluminosilicate gels. The structure of the gel and the connectivity of the Si and Al atoms in both the solid and liquid portions of the gel can be probed by NMR. Results are presented showing the applications of Si-29 MAS NMR to study the transformations occurring during the synthesis of NaY zeolite and the purely siliceous form of ZSM-5, known as silicalite. Structure directing tetrapropylammonium (TPA(+)) cations are required for the synthesis of silicalite. It is demonstrated that H-1-Si-29 and H-1-C-13 CP MAS NMR provide information about the relationship of the TPA(+) cations to the siliceous portions of the synthesis gel and about the conformation of the propyl groups of the cation. The use of liquid-line Si-29 and Al-27 NMR to identify the composition and structure of silicate and aluminosilicate species in TPA silicate and aluminosilicate solutions is illustrated as well. (C) 1999 Elsevier Science B.V. All rights reserved.