Theoretical Study of the MoS₂ (100) Surface:  A Chemical Potential Analysis of Sulfur and Hydrogen Coverage

Abstract

The stability of the (100) MoS2 surface has been studied using periodic DFT calculations taking into account various parameters such as the temperature and the partial pressure ratios of H2 and H2S present in the surrounding atmosphere. It appears that the sulfur coverage of the surface is strongly dependent on the H2/H2S ratio and that under working conditions, the most stable surface does not contain any coordinately unsaturated sites (CUS). Direct comparisons with experimental literature data such as EXAFS or TPR measurements show a good agreement between calculations and these experiments. The second part of the study deals with the behavior of hydrogen on the surfaces. The endothermic dissociation always leads to Mo−H and S−H groups. This implies that hydrogen is not stable on the MoS2 surface unless at very high pressure or very low temperature. Furthermore, H2 dissociation on the surface will not lead to the formation of CUS.

CO hydrogenation reaction on sulfided molybdenum catalysts

“…They found that under reductive condition adsorption of one CO molecule at the sulfur edge with about 50% S coverage is the most stable and exothermic by 0.7 eV. They also identified three thermodynamically stable surfaces for different H 2 /H 2 S pressure ratios which were also studied by Schweiger et al [24], Bollinger et al [27], Raybaud et al [33] and Cristol et al [34].…”

Hydrodeoxygenation of Phenolic Compounds by Sulfided (Co)Mo/Al2O3Catalysts, a Combined Experimental and Theoretical Study

“…A k-point mesh (3,1,1) has been chosen to give an accurate sampling of the supercell's Brillouin zone. Previous studies [29][30][31] showed that this model is suitable to predict the electronic and structural properties of the MoS 2 surface. A vacuum layer of 15 Å is located above the MoS 2 slab in the z direction to avoid interactions between slabs.…”

“…The two upper rows were allowed to relax until forces acting on ions are smaller than 3.10 -2 eV.Å -1 . The two lower rows were kept fixed to simulate bulk constraints [29][30][31]. The promoted catalyst is modeled by substituting of the Mo atoms on the S edge and half of the atoms on the metallic edge by Co (Fig.…”

“…For the reaction conditions used in the experimental studies, the most MoS 2 stable surface [21] is presented in Figure 1. This figure shows that the molybdenum edge is covered with sulfur atoms, yielding sixfold-coordinated Mo edge atoms [29,41]. Adsorption of large molecules will not be possible on this stable surface.…”

Description of coordinatively unsaturated sites regeneration over MoS2-based HDS catalysts using 35S experiments combined with computer simulations

“…On the other hand, with the recent developments of the computer simulations, new insights in the state of the HDS catalysts surface [81][82][83][84] as well as an overview of the HDS mechanism over the simulated surfaces were concurrently proposed [85,86]. Recently, we proposed for the first time a reliable CUS regeneration mechanism over MoS 2 crystallites by combining these two complementary methods [87,88].…”