抄録
The unique catalytic and adsorbent properties, crystal structures, ion-exchange and other characteristics of zeolites have been extensively investigated in recent years. The high-resolution solid-state 29Si-and 27Al-nuclear magnetic resonance (NMR) with magic angle spinning (MAS) have proved to be an useful tool for the chemical structural characterization of zeolites.
The article reviews how high-resolution solid-state NMR with MAS reveals unique insights into zeolite structures from recent literatures. Since five distinct Si-Al configurations, Si (OAl) n (OSi) 4-n (n=0-4), in zeolitic frameworks can be identified by 29Si-MAS NMR, several interesting problems have been enthusiastically discussed on 29Si-NMR analysis. In the present paper, the following topics are introduced and discussed:(1) Assignments of 29Si-chemical shifts and Si-Al configurations for aluminosilicates.(2) Discussion of Loewenstein's rule, the presence of Al-O-Al ordering, in the zeolite A.(3) Characteristic changes of Si/Al ratio in faujasites (zeolites X and Y) and mordenite studied by 29Si-NMR spectra.(4) 29Si-NMR spectral studies on the framework structures of pentasil zeolites such as ZSM-5, ZSM-11 and silicalite.(5) Stuidies of Ga3+ substitution for Al3+ in the zeolitic frameworks of faujasites studied by 29Si-NMR spectra.(6) Other 29Si-NMR spectral studies on zeolitic framework. On the other hand, 27Al-NMR has been used to estimate the compositions on tetrahedrally and octahedrally coordinated aluminum states. For instance, the dealumination mechanisms have been investigated by the 27Al-NMR spectral behaviors.
Furthermore the application of high-resolution solid-state 13C-NMR to the characteristic changes of organic compounds, in the zeolitic frameworks has been discussed.
