Characterization of Natural Zeolites and Clay Minerals by High-Resolution Solid-State NMR

Abstract

The use of the MAS techniques enables ²⁹Si-NMR to be obtained with the resolution of resonances from silicon atoms in chemically different microenvironments, namely different degrees of Si (nAl) coordinations in frameworks or layered structures and Si-O-Si bonding angles in silicate networks. On the other hand the use of the ²⁷Al-MASNMR techniques can result in the resolution of distinction of the Al (-O) coordination states.
In this paper, the following items are discussed:(1) The relation between ²⁹Si-chemical shifts and Si-Al micro-ordering (Si (nAl) configurations) for zeolites.(2) Si/A1 ratios of zeolitic frameworks.(3) Information of the Al (-0) coordination states obtained from ²⁷Al-MASNMR and Loewenstein's rule for aluminosilicate networks.(4) The applications of MASNMR to various natural zeolites; the comparison of the Si/A1 ratios of the framework structure with the bulk. The problems of identification “clinoptilolite” and “heulandite”(5) The ²⁹Si-and ²⁷Al-MASNMR investigations for various phyllosilicates: kaolinites (1: 1 dioctahedral), antigorite and chrysotile (1: 1 trioctahedral), pyrophyllite, montmorillonite and sericite (2: 1 dioctahedral), and talc, vermiculite and chlorite (2: 1 trioctahedral).(6) The unique ²⁹Si-and ²⁷Al-MASNMR results of sepiolite and attapulgite (palygorskite) with unusual phyllosilicate structures.(7) Detection of the microstructures by MASNMR for allophane, amorphous clay minerals.