Abstract
The formation of a silicoaluminophosphate-based molecular sieve SAPO-44 has been investigated in the present study. Particular attention was directed toward the characterization of the intermediate phases formed at different stages during the synthesis. The changes in the long-range ordering of the gel phases as a function of crystallization time was monitored by powder X-ray diffraction, and the development of the local structure of P, Al, and Si atoms was followed by 31P, 27Al, and 29Si magic-angle spinning NMR. 1H → 31P cross polarization (CP) was employed to differentiate the P sites in different phases coexisting in the sample. Several 27Al/31P and 27Al/29Si double-resonance NMR experiments such as CP and transferred echo double-resonance were also utilized to identify the nature of the intermediate phases, and to select the P−O−Al and Si−O−Al bonding connectivities. FT-Raman spectroscopy was used to gain the information regarding the evolution of the porosity in the framework and the immediate envir...
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