In Situ Multinuclear Magic-Angle Spinning NMR: Monitoring Crystallization of Molecular Sieve AlPO(4)-11 in Real Time

[Image: see text] Molecular sieves are crystalline three-dimensional frameworks with well-defined channels and cavities. They have been widely used in industry for many applications such as gas separation/purification, ion exchange, and catalysis. Obviously, understanding the formation mechanisms is fundamentally important. High-resolution solid-state NMR spectroscopy is a powerful method for the study of molecular sieves. However, due to technical challenges, the vast majority of the high-resolution solid-state NMR studies on molecular sieve crystallization are ex situ. In the present work, using a new commercially available NMR rotor that can withhold high pressure and high temperature, we examined the formation of molecular sieve AlPO(4)-11 under dry gel conversion conditions by in situ multinuclear ((1)H, (27)Al, (31)P, and (13)C) magic-angle spinning (MAS) solid-state NMR. In situ high-resolution NMR spectra obtained as a function of heating time provide much insights underlying the crystallization mechanism of AlPO(4)-11. Specifically, in situ (27)Al and (31)P MAS NMR along with (1)H → (31)P cross-polarization (CP) MAS NMR were used to monitor the evolution of the local environments of framework Al and P, in situ (1)H → (13)C CP MAS NMR to follow the behavior of the organic structure directing agent, and in situ (1)H MAS NMR to unveil the effect of water content on crystallization kinetics. The in situ MAS NMR results lead to a better understanding of the formation of AlPO(4)-11.