Ca. Fyfe et al., STRUCTURAL INVESTIGATIONS OF SAPO-37 MOLECULAR-SIEVE BY COHERENCE-TRANSFER AND DIPOLAR-DEPHASING SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE EXPERIMENTS, Microporous materials, 5(1-2), 1995, pp. 29-37
In this work, dipolar-based coherence-transfer and dipolar-dephasing s
olid-state nuclear magnetic resonance (NMR) experiments were performed
to investigate the structure of the silicoaluminophosphate molecular
sieve SAPO-37. The Al-27,Si-29 transferred-echo double-resonance (TEDO
R) experiment directly proves, for the first time, that silicon substi
tutes for phosphorus atoms in the framework via the SM2 mechanism. The
Al-27 (P-31) and Al-27 (Si-29) dipolar-dephasing difference experimen
ts and the two-dimensional Al-27-->P-31 TEDOR experiment indicate the
presence of three types of aluminum environments: tetrahedral Al surro
unded by symmetrical [4P] or [4Si] environments which give rise to a s
harp resonance, tetrahedral Al surrounded by asymmetrical [3P, Si], [2
P, 2Si] or [P, 3Si] environments which give rise to a broad resonance,
and also extra-framework amorphous octahedral Al.