Joo Paul H, Cheng Jianli, Yang Kesong
Department of NanoEngineering, University of California San Diego, La Jolla, CA 92093-0448, USA.
Phys Chem Chem Phys. 2017 Nov 15;19(44):29927-29933. doi: 10.1039/c7cp05402e.
Molybdenum disulfide (MoS) nanostructures have been widely used as catalysts in the petroleum refinery industry for the hydrodesulfurization process, in which sulfur vacancies play a critical role in determining the catalytic activity. Here we report size effects and odd-even effects on the formation of sulfur vacancies in the triangular MoS nanosheets using first-principles calculations. By modeling four types of edge structures of MoS nanosheets, S-terminated edges are found to be energetically more favorable than Mo-terminated edges, and are then selected for studying energetics of sulfur vacancies. Two types of sulfur dimer vacancies at the center (V@Cen) and at the corner (V@Cnr) of the edges of S-terminated MoS nanosheets are modeled, respectively. Our results reveal a strong odd-even effect on the formation of sulfur dimer vacancies, particularly for small MoS nanosheets, in terms of the size of nanosheets that is defined by the number of Mo atoms on the edge. The V@Cen dimer vacancy has a low formation energy at an even-number but a high formation energy at an odd-number, while the V@Cnr dimer vacancy exhibits a complete opposite trend. These results indicate that small MoS nanosheets can exhibit unique material properties for catalytic applications.
二硫化钼（MoS）纳米结构已在石油炼制工业的加氢脱硫过程中被广泛用作催化剂，其中硫空位在决定催化活性方面起着关键作用。在此，我们使用第一性原理计算报告了三角形MoS纳米片中硫空位形成的尺寸效应和奇偶效应。通过对MoS纳米片的四种边缘结构进行建模，发现S端边缘在能量上比Mo端边缘更有利，因此选择S端边缘来研究硫空位的能量学。分别对S端MoS纳米片边缘中心（V@Cen）和角落（V@Cnr）处的两种硫二聚体空位进行了建模。我们的结果表明，就由边缘上Mo原子数量定义的纳米片尺寸而言，硫二聚体空位的形成存在强烈的奇偶效应，特别是对于小尺寸的MoS纳米片。V@Cen二聚体空位在偶数时形成能较低，而在奇数时形成能较高，而V@Cnr二聚体空位则呈现完全相反的趋势。这些结果表明，小尺寸的MoS纳米片在催化应用中可能表现出独特的材料性能。
