郑健, 李强, 秦玉才, 宋丽娟. HFAU分子筛非骨架铝物种对Brønsted酸性质影响的理论研究[J]. 燃料化学学报（中英文）, 2022, 50(7): 849-858. DOI: 10.19906/j.cnki.JFCT.2022009
引用本文: 郑健, 李强, 秦玉才, 宋丽娟. HFAU分子筛非骨架铝物种对Brønsted酸性质影响的理论研究[J]. 燃料化学学报（中英文）, 2022, 50(7): 849-858. DOI: 10.19906/j.cnki.JFCT.2022009
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ZHENG Jian, LI Qiang, QIN Yu-cai, SONG Li-juan. Impact of the extra-framework aluminum species on the properties of Brønsted acid sites in HFAU zeolites by using thiophene probe molecule: A periodic DFT study[J]. Journal of Fuel Chemistry and Technology, 2022, 50(7): 849-858. DOI: 10.19906/j.cnki.JFCT.2022009
Citation: ZHENG Jian, LI Qiang, QIN Yu-cai, SONG Li-juan. Impact of the extra-framework aluminum species on the properties of Brønsted acid sites in HFAU zeolites by using thiophene probe molecule: A periodic DFT study[J]. Journal of Fuel Chemistry and Technology, 2022, 50(7): 849-858. DOI: 10.19906/j.cnki.JFCT.2022009
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HFAU分子筛非骨架铝物种对Brønsted酸性质影响的理论研究

Impact of the extra-framework aluminum species on the properties of Brønsted acid sites in HFAU zeolites by using thiophene probe molecule: A periodic DFT study

    摘要
  • 摘要: 以HFAU分子筛为研究对象，噻吩为探针分子，采用周期性密度泛函理论的方法探索Al(OH)2+和Al3+非骨架铝物种对Brønsted酸（简称B酸）性质的影响。通过对分子筛酸性位结构特性和电子性质的分析发现，Al3+非骨架铝物种的Lewis酸（简称L酸）强度高于Al(OH)2+非骨架铝物种，两个方向的Al(OH)2+羟基非骨架物种具有相似的电荷性质，即相似的酸强度。电子性质结合去质子化能的结果发现，1-HFAU/Al(OH)2+、2-HFAU/Al(OH)2+和HFAU/Al3+分子筛B酸中心具有相似的酸强度（1045 ± 11）kJ/mol。由此可得Al(OH)2+非骨架铝物种羟基方向的差异及Al(OH)2+和Al3+非骨架铝物种L酸强度的差异不影响B酸中心的酸强度。通过模拟噻吩分子的吸附发现，HFAU/Al3+分子筛中噻吩易于吸附在Al3+位（归因于Al3+中心的强L酸强度）。而HFAU/Al(OH)2+分子筛中的噻吩会优先吸附在B酸位（归因于Al(OH)2+物种自身的结构特性）。此外，Al(OH)2+非骨架铝物种可以对吸附在B酸位的噻吩施加一个弱的相互作用（色散作用）促进噻吩的吸附。吸附的模式依赖Al(OH)2+物种的结构和羟基的方向。此项工作从电子层面探究了主体HFAU分子筛（含非骨架铝）和客体噻吩分子的本征特性，揭示了活性位间的协同作用模式。

     

    Abstract: The effects of extra-aluminum species (Al(OH)2+and Al3+) on the properties of Brønsted acid sites (BAS) were studied using thiophene as the model probe and HFAU as model zeolite by using a periodic DFT study. It is found that the Lewis acid strength of Al3+ species is higher than that of Al(OH)2+ species, and the hydroxyl species Al(OH)2+ in both directions have similar charge properties, that is, similar acid strength. The results of electronic properties combined with deprotonation energies (DPE) show that the BAS in 1-HFAU/Al(OH)2+, 2-HFAU/Al(OH)2+and HFAU/Al3+ zeolites have similar acid strength (1045 ± 11 kJ/mol). It can be concluded that the difference of hydroxyl direction and Lewis acid strength of Al(OH)2+and Al3+ species hardly affect the acid strength of BAS. By simulating the adsorption of thiophene, the adsorption energies and the changes of electronic properties and geometric structure during the adsorption process were obtained. The results show that thiophene in HFAU/Al3+ zeolite is easy to be adsorbed on Al3+ site, which is due to the strong Lewis acid strength of Al3+ adsorption site. The thiophene in HFAU/Al(OH)2+ zeolite is preferentially adsorbed on the BAS rather than the Al(OH)2+ adsorption site. In addition, Al(OH)2+ species can exert a weak interaction (dispersion interaction) on thiophene adsorbed on BAS to promote the adsorption of thiophene. The adsorption modes depend on the structure of Al(OH)2+ species and the direction of hydroxyl groups. This work explored the intrinsic properties of host-HFAU zeolite (containing extra-framework aluminum species) and guest-thiophene molecule from an electronic-level, and revealed the synergistic mechanism between acid sites.

     

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