Adsorbate/adsorbent interactions in microporous zeolites: mechanistic insights from NMR relaxation and DFT calculations
Adsorbate/adsorbent interactions in microporous zeolites: mechanistic insights from NMR relaxation and DFT calculations
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DOI：
10.1016/j.mtchem.2023.101443
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发表时间：
2023-03-15
影响因子：
7.3
通讯作者：
Fan, X.
中科院分区：
文献类型：
--
作者：
D'Agostino, C.;Brauer, P.;Fan, X.
核磁共振弛豫技术是一种有效的、非侵入性的研究多孔材料中主客体相互作用的技术。特别是，横向核自旋弛豫时间常数T1/T2的比率已被证明是中孔介质中吸附质/吸附剂相互作用的稳健指标。然而，在微孔材料中使用NMR弛豫时间来探测相互作用和动力学仍然相对未被探索。在这里，我们调查和描述的微孔HZSM-5沸石中的铝含量对一系列常见的液体探针分子的NMR弛豫时间的影响。特别是，我们讨论的NMR弛豫时间行为的液体的亲水性（水，甲醇）和疏水性（甲苯，甲基环己烷）的性能吸附在HZSM-5样品具有不同的硅铝比（SAR 1/4 SiO2/Al 2 O3）。我们的结果表明，高极性分子对铝含量显示出高敏感性（即，表面酸性），对于更高酸性的沸石，T1/T2比率显著增加。相反，对于低极性分子，T1/T2比作为SAR的函数保持大致恒定，并且在低SAR的沸石中，与水和甲醇相比要低得多。密度泛函理论（DFT）的计算对比不同的SAR模型沸石结构内的水和甲苯的表面相互作用机制，并提供分子水平的洞察到NMR弛豫行为的观察到的趋势。(c)2023作者。由爱思唯尔有限公司出版。这是一篇开放获取的文章，使用CC BY许可证（http：//creativecommons.org/licenses/by/4.0/）。
Nuclear magnetic resonance (NMR) relaxation is an effective and non-invasive technique for probing guest-host interactions in porous materials. In particular, the ratio of longitudinal-to-transverse nuclear spin relaxation time constants T1/T2 has been demonstrated as a robust indicator of adsorbate/adsorbent interactions in mesoporous media. However, the use of NMR relaxation times in microporous materials to probe interactions and dynamics remains relatively unexplored. Herein, we investigate and describe the effect of the aluminium content in microporous HZSM-5 zeolites on the NMR relaxation times of a range of common liquid probe molecules. In particular, we discuss the NMR relaxation time behavior of liquids with hydrophilic (water, methanol) and hydrophobic (toluene, methyl cyclohexane) properties adsorbed over HZSM-5 samples with varying silica-to-alumina ratios (SAR 1/4 SiO2/Al2O3). Our results demonstrate that highly polar molecules show high sensitivity to aluminium content (i.e., surface acidity), with T1/T2 ratios increasing significantly for higher acidity zeolites. Conversely, for molecules with low polarity, the T1/T2 ratio as a function of SAR remains approximately constant, and in the zeolites with low SAR is much lower compared to that of water and methanol. Density functional theory (DFT) calculations are employed to contrast the surface interaction mechanisms of water and toluene within model zeolite structures of varying SAR, and provide molecular level insights into the observed trends in NMR relaxation behavior.(c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).