Alahakoon Sandamini H, Willans Mathew J, Huang Yining
Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada.
JACS Au. 2023 May 9;3(6):1670-1683. doi: 10.1021/jacsau.3c00109. eCollection 2023 Jun 26.
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-11 under dry gel conversion conditions by in situ multinuclear (H, Al, P, and 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-11. Specifically, in situ Al and P MAS NMR along with H → P cross-polarization (CP) MAS NMR were used to monitor the evolution of the local environments of framework Al and P, in situ H → C CP MAS NMR to follow the behavior of the organic structure directing agent, and in situ 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-11.
分子筛是具有明确通道和空腔的晶体三维骨架。它们在工业上已被广泛用于许多应用，如气体分离/净化、离子交换和催化。显然，了解其形成机制至关重要。高分辨率固态核磁共振光谱是研究分子筛的有力方法。然而，由于技术挑战，绝大多数关于分子筛结晶的高分辨率固态核磁共振研究都是非原位的。在本工作中，我们使用一种新型的可承受高压和高温的市售核磁共振转子，通过原位多核（H、Al、P和C）魔角旋转（MAS）固态核磁共振研究了干凝胶转化条件下分子筛AlPO-11的形成。作为加热时间函数获得的原位高分辨率核磁共振光谱为AlPO-11的结晶机制提供了许多深入见解。具体而言，原位Al和P MAS核磁共振以及H→P交叉极化（CP）MAS核磁共振用于监测骨架Al和P局部环境的演变，原位H→C CP MAS核磁共振用于追踪有机结构导向剂的行为，原位H MAS核磁共振用于揭示含水量对结晶动力学的影响。原位MAS核磁共振结果有助于更好地理解AlPO-11的形成。
