Characterization of MoSe2(0001) and ion-sputtered MoSe2 by XPS
Characterization of MoSe2(0001) and ion-sputtered MoSe2 by XPS
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DOI：
10.1007/s10853-005-2104-7
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发表时间：
2005-05-01
影响因子：
4.5
通讯作者：
Nelson, AE
中科院分区：
文献类型：
--
作者：
Abdallah, WA;Nelson, AE
二硫属钼（MoS 2、MoSe 2、MoTe 2）由于其作为催化剂[1-3]和光伏材料[4-6]的主要重要性而引起了极大的关注。这些材料具有由弱键合的X-Mo-X层（X= S、Se、Te）的堆叠产生的六方密堆积（hcp）结构，并产生高度各向异性特性[7]。其中，二硫化钼（MoS 2）已被广泛研究，主要是由于其作为加氢处理催化剂的相关性，以从各种油馏分中除去含硫和含氮化合物。MoS 2的大基面（0001）是相对无催化活性的，而边缘平面（S-边缘，1010; Moedge，1010）由于配位不饱和（cus）Mo（或促进剂）位点的存在而通常被接受为活性位点。MoS 2（0001）表面已被证明对噻吩无催化活性[8];然而，使用乙烷乙炔的其他研究表明轻微的反应性，表明在新切割的基底表面上存在cus位点。Wiegenstein和Schulz [9]证明，使用离子轰击可以增加cus Mo位点的密度，从而增加甲硫醇的反应性。MoS 2（0001）的XPS测量表明，（0001）表面的Mo 3d峰与Mo（IV）峰一致，退火至573 K后，结合能和结合强度没有明显变化。然而，离子轰击后的Mo 3d峰转移到一个更高的结合能与浓度的额外的Mo氧化态的缺陷的基底表面上一致。因此，可以使用受控离子轰击使MoS 2（0001）表面具有反应性以增加cus位点的密度。除了在光伏工业中的广泛应用外，MoSe 2还可能具有用作纳米结构加氢处理催化剂的潜力。例如，在脂肪族含氮分子的加氢脱氮（HDN）中CN键断裂的机理被认为是霍夫曼型消除或亲核取代[10-14]。这两种机制都需要一对位点：一个酸位点通过氮原子与氮分子反应，使胺基准备从分子中离开;一个碱性位点在消除机制中夺取β-氢，或亲核取代机制中攻击α-碳。先前已经提出，在MoS 2（1010）的促进的（Ni）边缘上，未覆盖的促进剂原子可以在MoS 2（1010）的表面上形成。
Molybdenum dichalcogenides (MoS2, MoSe2, MoTe2) have attracted significant attention because of their primary importance as catalysts [1–3] and photovoltaic materials [4–6]. These materials have a hexagonal closed packed (hcp) structure that results from the stacking of weakly bonded X-Mo-X layers (X= S, Se, Te) and gives rise to highly anisotropic properties [7]. Of these, molybdenum disulfide (MoS2) has been widely studied primarily due to its relevance as a hydrotreating catalyst to remove sulfur-and nitrogencontaining compounds from various oil fractions. The large basal plane (0001) of MoS2 is relatively catalytically inactive, while the edge planes (S-edge, 1010; Moedge, 1010) are generally accepted to be the active sites due to the presence of coordinatively unsaturated (cus) Mo (or promoter) sites. The MoS2 (0001) surface has been shown to be catalytically inactive toward thiophene [8]; however, additional studies with ethanethiol have indicated slight reactivity suggesting the presence of cus sites on the freshly cleaved basal surface. Wiegenstein and Schulz [9] demonstrated the density of cus Mo sites can be increased using ion bombardment, thereby increasing the reactivity of methanethiol. Their XPS measurements of MoS2 (0001) indicated that the Mo 3d peaks of a (0001) surface are consistent with Mo (IV), and no significant change in binding energy or intensity was observed after annealing to 573 K. However, following ion bombardment the Mo 3d peaks shifted to a higher binding energy consistent with a concentration of additional Mo oxidation states on the defective basal surface. Consequently, the MoS2 (0001) surface can be made reactive using controlled ion bombardment to increase the density of cus sites. In addition to the widespread application in the photovoltaic industry, MoSe2 may also have the potential to be used as a nanostructured hydrotreating catalyst. For example, the mechanism of CN bond cleavage in the hydrodenitrogenation (HDN) of aliphatic nitrogen-containing molecules has been suggested to be Hofmann-type elimination or nucleophilic substitution [10–14]. Both of these mechanisms require a pair of sites: an acid site to react with the nitrogenmolecule through the nitrogen atom, making the amine group ready to leave from the molecule; and a basic site to abstract the β-hydrogen in the elimination mechanism, or a nucleophile to attack the α-carbon in the nucleophilic substitution mechanism. It has been previously suggested that on a promoted (Ni) edge of MoS2 (1010), the uncovered promoter atoms can ac-