H2在Mo x S y 团簇上吸附解离的尺寸效应研究

doi:10.11949/0438-1157.20220539

摘要/Abstract

摘要：

浆态床加氢工艺可以处理不同来源的劣质重油、渣油，氢气的活化是重油加氢处理过程中发生的主要反应之一。钼基催化剂的分散性是影响重油加氢活性的关键因素。构建了Mo₇S₁₅、Mo₁₂S₂₆、Mo₁₈S₃₉、Mo₂₅S₅₄和Mo₃₃S₇₁团簇，利用密度泛函理论研究了团簇自身的稳定性、活性以及H₂在不同尺寸团簇上的吸附与解离过程。结果发现，在目前所建立的团簇中，其尺寸越小，结合能越低，最高占据分子轨道-最低未占分子轨道(HOMO-LUMO)能隙值越小，团簇稳定性越弱，活性越强。H₂在簇上的稳定吸附位点为边缘位点。随团簇尺寸增大，吸附能分别为-64.25、-34.60、-34.14、-7.20、-6.82 kJ/mol，吸附能绝对值减小，氢气分子与团簇的相互作用减弱，并且解离能逐渐增大，分别为13.76、33.14、53.64、60.75、64.47 kJ/mol。目前的结果表明，团簇尺寸越小，氢气的吸附解离越容易，显示出更高的活性。

关键词: Mo _x S _y 团簇, 团簇尺寸, 氢气活化, 钼基催化剂, 密度泛函理论

Abstract:

Slurry bed hydrotreating process can treat inferior heavy oil and residual oil from different sources. Therefore, compared with other processes, the process is characterized by strong adaptability of raw materials. One of the main reactions of heavy oil hydrotreating is the activation of hydrogen. Molybdenum-based dispersed catalyst is widely used as an efficient hydrogenation catalyst in the slurry bed hydrogenation process. One of the key factors affecting the hydrogenation activity of heavy oil is the dispersion of molybdenum-based catalysts. Therefore, it is meaningful to explore the dispersion of the catalyst for hydrogen activation. In this paper, Mo₇S_15, Mo₁₂S₂₆, Mo₁₈S₃₉, Mo₂₅S₅₄ and Mo₃₃S₇₁ clusters were built and their structure is optimized. On the basis of stable structure, the stability and activity of clusters with different sizes were studied, and the adsorption dissociation process of hydrogen on Mo _x S _y clusters with different sizes was discussed, including the stability of hydrogen molecules at different adsorption sites, the adsorption dissociation process of hydrogen molecules on Mo _x S _y clusters with different sizes, and the changes with the size of Mo _x S _y clusters. According to the calculation results, it is found that the currently established clusters with smaller size have the lower binding energy, the smaller HOMO-LUMO energy gap value, the weaker stability and the stronger activity. During the adsorption and dissociation of H₂ above the cluster, it is found that hydrogen is more easily adsorbed at the edge position. With the increase of cluster size, the adsorption energy was -64.25, -34.60, -34.14, -7.20 and -6.82 kJ/mol; the absolute value of the adsorption energy decreased; the interaction between hydrogen molecules and the cluster was weaker; the dissociation energy gradually increased, and were 13.76, 33.14, 53.64, 60.75 and 64.47 kJ/mol, respectively. The current results show that the smaller the cluster size, the easier it is for hydrogen to adsorb/ dissociate and the cluster shows higher activity.

Key words: Mo _x S _y cluster, cluster size, hydrogen activation, Mo-based catalyst, density functional theory

中图分类号:

O 643.36

杜峰, 尹思琦, 罗辉, 邓文安, 李传, 黄振薇, 王文静. H₂在Mo _x S _y 团簇上吸附解离的尺寸效应研究[J]. 化工学报, 2022, 73(9): 3895-3903.

Feng DU, Siqi YIN, Hui LUO, Wenan DENG, Chuan LI, Zhenwei HUANG, Wenjing WANG. Study on size effect of H₂ adsorption and dissociation on Mo _x S _y clusters[J]. CIESC Journal, 2022, 73(9): 3895-3903.

图/表 10

图1 五种不同尺寸的Mo x S y 团簇模型Sc—角硫原子;Moe—边缘钼原子;Se—边缘硫原子

Fig.1 Five different sizes of Mo x S y cluster modelSc—corner sulfur atom; Moe—edge molybdenum atom; Se—edge sulfur atom

表1 Mo x S y 团簇、钼原子、硫原子的能量E及不同尺寸Mo x S y （x=7，12，18，25，33； y=15，26，39，54，71）团簇的平均结合能Eb

Table 1 Energy E of Mo x S y clusters， molybdenum atoms， sulfur atoms and binding energies Eb of Mo x S y （x=7，12，18，25，33； y=15，26，39，54，71） clusters with different sizes

Energy	Mo	S	Mo₇S₁₅	Mo₁₂S₂₆	Mo₁₈S₃₉	Mo₂₅S₅₄	Mo₃₃S₇₁
E/eV	-1855.00	-10832.37	-175589.75	-304118.30	-456185.94	-631793.35	-830940.07
E_b/eV	—	—	5.42	5.70	5.85	5.95	6.03

表2 Mo x S y （x=7，12，18，25，33； y=15，26，39，54，71）团簇的HOMO-LUMO能隙值Eg

Table 2 HOMO-LUMO energy gap values of Mo x S y （x=7，12，18，25，33； y=15，26，39，54，71） cluster Eg

System	E(HOMO)/eV	E(LUMO)/eV	E_g/eV
Mo₇S₁₅	-5.539	-5.431	0.108
Mo₁₂S₂₆	-5.409	-5.289	0.120
Mo₁₈S₃₉	-5.469	-5.337	0.132
Mo₂₅S₅₄	-5.612	-5.266	0.346
Mo₃₃S₇₁	-5.814	-5.280	0.534

表3 氢气在不同尺寸团簇边缘位和角位的吸附结构参数、吸附能（Eads）

Table 3 Adsorption structure parameters and adsorption energy （Eads） of hydrogen at the edges and corners of clusters with different sizes

Species	Corners			Edges
Species	r_(H—H)/nm	r_(H—S)/nm	E_ads/(kJ/mol)	r_(H—H)/nm	r_(H—Mo)/nm	r_(H—S)/nm	E_ads/(kJ/mol)
Mo₇S₁₅H₂	0.0772	0.292	-48.58	0.0773	0.220	0.271	-64.25
Mo₁₂S₂₆H₂	0.0749	0.359	-14.62	0.0769	0.228	0.273	-34.60
Mo₁₈S₃₉H₂	0.0748	0.362	-14.26	0.0763	0.231	0.275	-34.14
Mo₂₅S₅₄H₂	0.0748	0.365	-7.13	0.0750	0.311	0.297	-7.20
Mo₃₃S₇₁H₂	0.0748	0.370	-5.59	0.0748	0.332	0.319	-6.82

图2 不同尺寸Mo x S y 团簇边缘位点处Mo 4d、S 3p与H 1s轨道投影态密度图：(a) Mo7S15团簇; (b) Mo12S26团簇; (c) Mo18S39团簇; (d) Mo25S54团簇; (e) Mo33S71团簇

Fig.2 PDOS of Mo 4d, S 3p and H 1s orbitals at edge sites of Mo x S y clusters with different sizes:(a) Mo7S15 clusters; (b) Mo12S26 clusters; (c) Mo18S39 clusters; (d) Mo25S54 clusters; (e) Mo33S71 clusters

图3 H2在Mo7S15团簇上解离的初态（Mo7S15H2-R）、过渡态（Mo7S15H2-TS）及末态（Mo7S15H2-P）的优化构型

Fig.3 The optimized configuration of initial state (Mo7S15H2-R), transition state (Mo7S15H2-TS) and final state (Mo7S15H2-P) of H2 dissociation on Mo7S15 clusters

图4 氢气分子在Mo x S y (x=7,12,18,25,33; y=15,26,39,54,71)团簇上的吸附解离过程：(a) Mo7S15团簇; (b) Mo12S26团簇; (c) Mo18S39团簇; (d) Mo25S54团簇; (e) Mo33S71团簇

Fig.4 Adsorption and dissociation process of hydrogen molecules on Mo x S y (x=7,12,18,25,33; y=15,26,39,54,71) clusters:(a) Mo7S15 clusters; (b) Mo12S26 clusters; (c) Mo18S39 clusters; (d) Mo25S54 clusters; (e) Mo33S71 clusters

表4 氢气在Mo x S y （x=7，12，18，25，33； y=15，26，39，54，71）团簇上的解离能垒Ea以及初态（R）、过渡态（TS）、末态（P）的构型参数

Table 4 Dissociation barriers Ea of hydrogen on Mo x S y （x=7，12，18，25，33； y=15，26，39，54，71） clusters and configuration parameters of initial state（R）， transition states（TS） and final state（P）

Species	r_(H—H) /nm	r_(H—Mo)/nm	r_(H—S)/nm	E_a/ (kJ/mol)
Mo₇S₁₅H₂-R	0.0773	0.2200	0.2710	13.76
Mo₇S₁₅H₂-TS	0.1084	0.1824	0.2553
Mo₇S₁₅H₂-P	0.2241	0.1693	0.1362
Mo₁₂S₂₆H₂-R	0.0769	0.2280	0.2730	33.14
Mo₁₂S₂₆H₂-TS	0.1035	0.1828	0.1593
Mo₁₂S₂₆H₂-P	0.2310	0.1690	0.1364
Mo₁₈S₃₉H₂-R	0.0763	0.2310	0.2750	53.64
Mo₁₈S₃₉H₂-TS	0.1102	0.1809	0.1517
Mo₁₈S₃₉H₂-P	0.2252	0.1685	0.1362
Mo₂₅S₅₄H₂-R	0.0750	0.3110	0.2970	60.75
Mo₂₅S₅₄H₂-TS	0.1096	0.1807	0.1531
Mo₂₅S₅₄H₂-P	0.2252	0.1688	0.1361
Mo₃₃S₇₁H₂-R	0.0748	0.3320	0.3190	64.47
Mo₃₃S₇₁H₂-TS	0.1045	0.1827	0.1576
Mo₃₃S₇₁H₂-P	0.2292	0.1690	0.1364

图5 催化剂尺寸与TOF值的相关性

Fig.5 Correlation between catalyst size and TOF value

图6 解离能垒Ea与结合能Eb关联图

Fig.6 Correlation diagram between dissociation energy barrier Ea and binding energy Eb

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H₂在Mo _x S _y 团簇上吸附解离的尺寸效应研究

Study on size effect of H₂ adsorption and dissociation on Mo _x S _y clusters

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