DFT calculations of unpromoted and promoted MoS2-based hydrodesulfurization catalysts
DFT calculations of unpromoted and promoted MoS2-based hydrodesulfurization catalysts
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DOI：
10.1006/jcat.1999.2598
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发表时间：
1999-10-01
影响因子：
7.3
通讯作者：
Topsoe, H
中科院分区：
文献类型：
--
作者：
Byskov, LS;Norskov, JK;Topsoe, H
用自洽密度泛函理论(DFT)研究了MoS_2基加氢脱硫(HDS)催化剂的结构和活性中心。由单层MoS_2链组成的模型被用来描述催化剂中的结构，并允许完全松弛来寻找最低能量构型。结果表明，最受欢迎的边缘结构明显偏离了文献中所考虑的结构和从体相MoS_2结构的简单终止所预期的结构。计算还表明，助剂原子更倾向于位于所谓的硫端((1)在第010条上)MoS_2边缘。尽管这种结构以前没有被考虑过，但人们发现它们与扩展X射线吸收精细结构(EXAFS)实验中获得的结构信息是一致的。由于硫空位的产生被认为是许多加氢处理反应的第一步，因此也计算了从不同结构中脱除硫所需的能量。与MoS_2、Co-Mo-S、Ni-Mo-S和Fe-Mo-S结构的催化活性比较表明，金属硫结合能最低的结构具有最高的加氢脱附活性，与键能模型基本一致。基于一个简单的LCAO模型，对MoS_2促进结构中的硫键进行了更详细的分析，解释了不同促进行为的起源。最后，讨论了氢在不同结构上的吸附。我们发现氢在硫原子边缘的吸附很强，并推测在催化过程中，S边缘被SH基团部分覆盖，(C)1999学术出版社。
Self-consistent density functional theory (DFT) is used to study the structure and active sites in unpromoted and promoted MoS2-based hydrodesulfurization (HDS) catalysts. A model consisting of single-layer MoS2 chains with and without promoter atoms located at the edges is used to represent the structures in the catalysts, and full relaxation is allowed to find the lowest energy configurations. The results show that the most favored edge structures deviate significantly from those considered in the literature and those expected from simple terminations of the bulk MoS2 structures. The calculations also show that the promoter atoms prefer to be located at the so-called sulfur-terminated ((1) over bar 010) MoS2 edges. Although such structures have not been considered previously it is found that they are in agreement with available structural information from Extended X-Ray Absorption Fine Structure (EXAFS) experiments. Since the creation of sulfur vacancies is believed to be the first step for many hydrotreating reactions, the energy required to remove sulfur from the different structures has also been calculated. Comparison with catalytic activity results for MoS2, Co-Mo-S, Ni-Mo-S, and Fe-Mo-S structures shows that the highest HDS activity is obtained for the structures with the lowest metal sulfur binding energy, in general agreement with the bond energy model (BEM). A more detailed analysis of the sulfur bonding in promoted MoS2 structures based on a simple LCAO-type model explains the origin of the different promotional behaviors. Finally, the adsorption of hydrogen on the different structures is discussed. We find hydrogen adsorption at edge sulfur atoms to be strong, and suggest that the S-edge is partly covered by SH groups during catalysis, (C) 1999 Academic Press.