Laboratoire de Chimie Inorganique et Biologique, UMR-E CEA/UJF-Grenoble, Institut Nanosciences et Cryogénie, France.
J Am Chem Soc. 2012 Nov 14;134(45):18491-4. doi: 10.1021/ja307755t. Epub 2012 Nov 2.
By means of a true sensitivity enhancement for a solid-state NMR spectroscopy (SSNMR) experiment performed under dynamic nuclear polarization (DNP) conditions, corresponding to 4-5 orders of magnitude of time savings compared with a conventional SSNMR experiment, it is shown that it is possible to record interface-selective (27)Al-(27)Al two-dimensional dipolar correlation spectra on mesoporous alumina, an advanced material with potential industrial applications. The low efficiency of cross-polarization and dipolar recoupling for quadrupolar nuclei is completely negated using this technique. The important presence of pentacoordinated Al has not only been observed, but its role in bridging interfacial tetra- and hexacoordinated Al has been determined. Such structural information, collected at low temperature (∼103 K) and 9.4 T with the use of DNP, would have been impossible to obtain under standard conditions, even using a higher magnetic field. However, here it is demonstrated that this information can be obtained in only 4 h. This work clearly opens a new avenue for the application of SSNMR to quadrupolar nuclei and notably the atomic-scale structure determination of catalysis materials such as mesoporous alumina.
通过对在动态核极化 (DNP) 条件下进行的固态核磁共振波谱学 (SSNMR) 实验进行真正的灵敏度增强，与传统的 SSNMR 实验相比，相应地节省了 4-5 个数量级的时间，这表明有可能在介孔氧化铝上记录界面选择性（27）Al-（27）Al 二维偶极相关光谱，介孔氧化铝是一种具有潜在工业应用的先进材料。该技术完全否定了用于四极核的交叉极化和偶极再结合的低效率。不仅观察到了五配位 Al 的重要存在，而且还确定了其在桥连界面四配位和六配位 Al 中的作用。在使用 DNP 在低温（约 103 K）和 9.4 T 下收集的这种结构信息，即使使用更高的磁场，在标准条件下也不可能获得。然而，这里证明仅需 4 小时即可获得此信息。这项工作显然为 SSNMR 在四极核中的应用开辟了新的途径，特别是为介孔氧化铝等催化材料的原子尺度结构确定开辟了新的途径。
