Characterization of the Gel Phases of AlPO4-11 Molecular Sieve Synthesis by Solid-state NMR

Abstract

We have used several solid-state NMR techniques in conjunction with powder X-ray diffraction (XRD) and FT-Raman spectroscopy to characterize the structures of the intermediate phases of AlPO4-11 molecular sieve synthesis. The evolution of the gel phases as a function of crystallization time was followed by 31P and 27Al magic angle spinning (MAS) NMR to obtain information on the local environments of Al and P atoms and by powder XRD to detect the long range ordering of the gel samples. We have utilized 27Al triple-quantum MAS (3QMAS) to gain additional resolution for monitoring the incorporation of different Al sites into the framework during the crystallization. 27Al/31P double resonance techniques such as cross polarization (CP), transfer of populations by double-resonance, and rotational echo double-resonance have been utilized to select the 31P−O−27Al bonding connectivities within the gel phases. The 1H → 31P CP enables differentiation of the phosphorus sites in different phases coexisting in the same ...