First Application of 27Al Multiple Quantum Magic-Angle Spinning Nuclear Magnetic Resonance at 16.4 T to Inorganic Matter in Natural Coals
First Application of 27Al Multiple Quantum Magic-Angle Spinning Nuclear Magnetic Resonance at 16.4 T to Inorganic Matter in Natural Coals
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DOI：
10.1021/ef040029e
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发表时间：
2004-08
期刊：
影响因子：
5.3
通讯作者：
K. Kanehashi;K. Saito
中科院分区：
文献类型：
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作者：
K. Kanehashi;K. Saito
首次将强磁场（16.4T）下的27 Al多量子魔角自旋（MQMAS）光谱应用于天然煤中无机物的结构分析。在7.0 T的3QMAS光谱的分辨率是不够的，用于识别天然煤中的无机物，因为不完全取消的二阶四极效应，虽然3QMAS光谱给出了更好的分辨率比常规魔角旋转（MAS）光谱。另一方面，增加磁场（16.4 T）大大提高了3QMAS光谱分辨率相比，在7.0 T，因此，它有利于一些矿物的分配。此外，在16.4 T下记录的3QMAS光谱导致信号增强的1/14，与在7.0 T下获得的光谱相比。更高的场强成为有用的分析无机物在天然煤中，具有低浓度的铝（10.2.0质量%）。并对16.4T下的3QMAS和5 QMAS谱进行了比较。对于天然煤中的无机物，3QMAS和5 QMAS的光谱分辨率几乎没有变化，尽管5量子相干态的激发效率不如3量子相干态。结果表明，MQMAS技术与强磁场相结合是一种非常有效的天然煤中无机物的表征方法，特别适用于低结晶度粘土矿物的分析。
27Al multiple quantum magic-angle spinning (MQMAS) spectroscopy at high magnetic field (16.4 T) was applied for the first time to the structural analysis of inorganic matter in natural coals. Resolution of 3QMAS spectra at 7.0 T was insufficient for identification of the inorganic matter in natural coals, because of incomplete cancellation of the second-order quadrupolar effects, although 3QMAS spectra gave better resolution than conventional magic-angle spinning (MAS) spectra. On the other hand, an increased magnetic field (16.4 T) greatly improved 3QMAS spectral resolution, compared to that obtained at 7.0 T; hence, it facilitated the assignment of some minerals. Moreover, 3QMAS spectra recorded at 16.4 T led to signal enhancement by a factor of ∼4, compared to spectra taken at 7.0 T. Higher field strengths became useful for the analysis of inorganic matter in natural coals that have a low concentration of aluminum (∼2.0 mass %). 3QMAS and 5QMAS spectra at 16.4 T were also compared. As far as inorganic matter in natural coals is concerned, the spectral resolution was almost unchanged between 3QMAS and 5QMAS, although the excitation of 5 quantum coherences is less efficient than that for 3 quantum coherences. It is concluded that the combination of MQMAS techniques with high magnetic field is a very effective for characterization of inorganic matter in natural coals and is especially well-suited to the analysis of clay minerals that have low crystallinity.