HFAU分子筛非骨架铝物种对Brønsted酸性质影响的理论研究

郑健; 李强; 秦玉才; 宋丽娟

doi:10.19906/j.cnki.JFCT.2022009

HFAU分子筛非骨架铝物种对Brønsted酸性质影响的理论研究

doi: 10.19906/j.cnki.JFCT.2022009

郑健^{1, 2,},
李强²,
秦玉才^2,,
宋丽娟^{1, 2, ,}

1.
中国石油大学(华东) 化学工程学院, 山东青岛 266555
2.
辽宁石油化工大学石油化工催化科学与技术重点实验室, 辽宁抚顺 113001

基金项目: 国家自然科学基金(21902068, U20A20120, U1908203)和中国石油创新基金(2020D-5007-0401)资助

详细信息

通讯作者:
Tel: 13941350056, E-mail: lsong56@263. net

中图分类号: O643
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出版历程
- 收稿日期: 2022-01-02
- 修回日期: 2022-01-16
- 录用日期: 2022-01-25
- 网络出版日期: 2022-02-12
- 刊出日期: 2022-08-01

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

ZHENG Jian^{1, 2
,},
LI Qiang²,
QIN Yu-cai^2
,,
SONG Li-juan^{1, 2
, ,}

1.
College of Chemistry & Chemical Engineering, China University of Petroleum (East China), Qingdao 266555, China
2.
Key Laboratory of Petrochemical Catalytic Science and Technology, Liaoning petrochemical University, Fushun 113001, China

Funds: The project was supported by the National Natural Science Foundation of China (21902068, U20A20120, U1908203) and PetroChina Innovation Foundation (2020D-5007-0401)

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。
- HFAU分子筛 /
- 活性位 /
- 密度泛函理论(DFT) /
- 协同作用机制 /
- 电子性质
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.
- HFAU zeolites /
- active sites /
- density functional theory (DFT) /
- synergistic mechanism /
- electronic properties

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FIG. 1683. FIG. 1683.

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图 1 三斜菱状分子筛单胞模型优化结构

Figure 1 Optimized structure of HFAU zeolite models

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图 2 分子筛B酸位和L酸位（Al(OH)²⁺和Al³⁺）的局部结构

Figure 2 Local structure of Brønsted and Lewis acid sites (Al(OH)²⁺ and Al³⁺) of zeolites

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图 3 分子筛B酸位的去质子化能

Figure 3 Deprotonation energies of Brønsted acid site (BAS) in zeolites

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图 4 噻吩分子的福井函数图

Figure 4 Fukui function of thiophene molecule

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图 5 分子筛中重要的分子轨道

Figure 5 Important molecular orbitals in zeolites

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图 6 分子筛中重要分子轨道的能量

Figure 6 Energies of important molecular orbitals in zeolites

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图 7 噻吩在HFAU/Al³⁺分子筛Lewis酸位的吸附能和吸附构型

Figure 7 Adsorption energies and configuration of thiophene on Lewis site in HFAU/Al³⁺ zeolites

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图 8 噻吩在HFAU/Al³⁺分子筛Al³⁺位点吸附的差分电子密度图

Figure 8 Electron density difference of thiophene on Al³⁺ sites in HFAU/Al³⁺ zeolite

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图 9 噻吩在HFAU/Al(OH)²⁺分子筛Al(OH)²⁺位点的吸附构型

Figure 9 Adsorption mode of thiophene on Al(OH)²⁺ sites in HFAU/Al(OH)²⁺ zeolite

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图 10 噻吩在HFAU/Al(OH)²⁺分子筛B酸和L酸(Al(OH)²⁺)位点的吸附能

Figure 10 Adsorption energies of thiophene on BAS and Al(OH)²⁺ site in HFAU/Al(OH)²⁺ zeolite

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图 11 噻吩在分子筛B酸位点的吸附构型和差分电子密度

Figure 11 Adsorption structure and electron density difference of thiophene on BAS in zeolites

(a), (d): 1-HFAU/Al(OH)²⁺; (b), (e): 2-HFAU/Al(OH)²⁺; (c), (f): HFAU/Al³⁺

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图 12 噻吩在分子筛B酸位点的吸附能

Figure 12 Adsorption energies of thiophene on BAS in zeolites

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表 1 1-HFAU/Al(OH)²⁺、2-HFAU/Al(OH)²⁺和HFAU/Al³⁺分子筛酸性位的电荷性质

Table 1 Charge properties of acid sites in 1-HFAU/Al(OH)²⁺, 2-HFAU/Al(OH)²⁺ and HFAU/Al³⁺

Atoms	1-HFAU/Al(OH)²⁺	2-HFAU/Al(OH)²⁺	HFAU/Al³⁺
T1	2.03	2.24	2.02
T2	2.25	2.03	2.21
T3	2.25	2.25	2.02
T4	2.03	2.25	2.20
T5	2.24	2.03	2.02
T6	2.24	2.24	2.21
O1	−1.19	−1.21	−1.19
O2	−1.14	−1.19	−1.20
O3	−1.19	−1.14	−1.18
O4	−1.21	−1.19	−1.20
O5	−1.13	−1.21	−1.19
O6	−1.21	−1.13	−1.20
Al7	2.08	2.08	2.08
O7	−1.11	−1.11	−1.11
Si7	2.33	2.33	2.33
H7	0.55	0.55	0.55
Al_EF	1.93	1.93	2.02
O	−1.12	−1.13	−
H	0.51	0.51	−

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表 2 噻吩在HFAU/Al³⁺分子筛Al³⁺位点吸附前后C–C键和C–S键的变化

Table 2 Changes of C–C and C–S bonds of thiophene adsorbed on Al³⁺ site in HFAU/Al³⁺ zeolite

Bond	d/nm
Bond	Free-TP	TP(C)-HFAU/Al³⁺	TP(S)-HFAU/Al³⁺
C1–C2	0.138	0137	0.136
C2–C3	0.143	0.145	0.144
C3–C4	0.138	0.142	0.136
C4–S	0.172	0.169	0.176
C1–S	0.172	0.173	0.176

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