Hinnemann Berit, Nørskov Jens K, Topsøe Henrik
Center for Atomic-scale Materials Physics, Department of Physics, Building 307, Technical University of Denmark, DK-2800 Lyngby, Denmark.
J Phys Chem B. 2005 Feb 17;109(6):2245-53. doi: 10.1021/jp048842y.
Density functional theory is used to investigate the origin of the activity differences between Type I and Type II MoS2-based structures in hydrotreating catalysts. It is well known that the Type II structures, where only weak interactions with the support exist, have a higher catalytic activity than Type I structures, where Mo-O linkages to the alumina are present. The present results show that the differences in activities for MoS2 and Co-Mo-S structures can be attributed to the electronic and bonding differences introduced by the bridging O bonds. We find that the Mo-O linkages are most probably located on the (1010) S edge. The presence of oxygen linkages increases the energy required to form sulfur vacancies significantly so that almost no vacancies can be formed at these and neighboring sites. In this way, the reactivity of the S edge is reduced. In addition, the studies also show that the linkages introduce changes in the one-dimensional metallic-like brim states. Furthermore, the presence of oxygen linkages also changes the energetics of hydrogen adsorption, which becomes less exothermic on sulfur sites directly above linkages and more exothermic on sulfur sites adjacent to linkages. The present results explain previously observed differences in Type I-Type II transition temperatures for Co-Mo-S structures with different Co contents.
密度泛函理论用于研究加氢处理催化剂中I型和II型MoS₂基结构活性差异的起源。众所周知，II型结构与载体仅有弱相互作用，其催化活性高于I型结构，I型结构中存在Mo与氧化铝的Mo - O键。目前的结果表明，MoS₂和Co - Mo - S结构活性的差异可归因于桥连O键引入的电子和键合差异。我们发现Mo - O键很可能位于(1010) S边缘。氧键的存在显著增加了形成硫空位所需的能量，使得在这些位点及相邻位点几乎无法形成空位。这样一来，S边缘的反应活性降低。此外，研究还表明这些键会引起一维类金属边缘态的变化。而且，氧键的存在也改变了氢吸附的能量学，在键上方的硫位点上氢吸附放热减少，而在与键相邻的硫位点上氢吸附放热增加。目前的结果解释了先前观察到的不同Co含量的Co - Mo - S结构在I型 - II型转变温度上的差异。
