Despite the extensive industrial and research interests in zeolites, their intrinsic catalytic nature is not fully understood due to the complexity of the hydroxyl-aluminum moieties. ¹⁷O NMR would provide irreplaceable opportunities for much-needed fine structural determination given the ubiquitous presence of oxygen atoms in nearly all species; however, the low sensitivity and quadrupolar nature of oxygen-17 make its NMR spectroscopic elucidation challenging. Here, we show that state-of-the-art double resonance solid-state NMR techniques have been combined with spectral editing methods based on scalar (through-bond) and dipolar (through-space) couplings, which allowed us to address the subtle protonic structures in zeolites. Notably, the often-neglected and undesired second-order quadrupolar-dipolar cross-term interaction (“2nd-QD interaction”) can actually be exploited and can help gain invaluable information. Eventually, a comprehensive set of ¹H–¹⁷O/¹H–²⁷Al double resonance NMR with J-/D-coupling spectral editing techniques have been designed in this work and enabled us to reveal atomic-scale precise structural and dynamical details in zeolites including: 1) The jump rate of the bridging acid site (BAS) proton is relatively low, i.e., far less than 100 s^–1 at room temperature. 2) The Al–OH groups with ¹H chemical shift at 2.6–2.8 ppm, at least for nonseverely dealuminated H-ZSM-5 catalysts, exhibit a rigid bridging environment similar to that of BAS. 3) The Si–OH groups at 2.0 ppm are not hydrogen bonded and undergo fast cone-rotational motion. The results in this study predict the 2nd-QD interaction to be universal for any rigid −¹⁷O–H environment, such as those in metal oxide surfaces or biomaterials.

中文翻译：

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耦合编辑 1H–17O 双共振 NMR 光谱揭示了沸石的精确结构和动力学细节

尽管沸石引起了广泛的工业和研究兴趣，但由于羟基铝部分的复杂性，其内在催化性质尚未完全了解。鉴于几乎所有物种中都普遍存在氧原​​子， ¹⁷ O NMR 将为急需的精细结构测定提供不可替代的机会；然而，O-17 的低灵敏度和四极性质使其核磁共振波谱解析具有挑战性。在这里，我们展示了最先进的双共振固态核磁共振技术与基于标量（通过键合）和偶极（通过空间）耦合的光谱编辑方法相结合，这使我们能够解决微妙的问题沸石中的质子结构。值得注意的是，经常被忽视和不受欢迎的二阶四极-偶极交叉项相互作用（“二阶量子点相互作用”）实际上可以被利用，并且可以帮助获得宝贵的信息。最终，在这项工作中设计了一套全面的¹ H– ¹⁷ O/ ¹ H– ²⁷ Al 双共振 NMR 和J -/ D耦合光谱编辑技术，使我们能够揭示原子尺度的精确结构和动力学细节。沸石包括： 1)桥酸位(BAS)质子的跃迁速率相对较低，即在室温下远小于100 s ^{–1 。 2) 1} H 化学位移为 2.6-2.8 ppm的 Al-OH 基团，至少对于非严重脱铝的 H-ZSM-5 催化剂来说，表现出类似于 BAS 的刚性桥接环境。 3) 2.0 ppm 的 Si-OH 基团不是氢键，并且进行快速锥体旋转运动。这项研究的结果预测，第二量子点相互作用对于任何刚性 - ¹⁷ O–H 环境都是普遍的，例如金属氧化物表面或生物材料中的环境。