Electronic structure and reactivity of defect MoS2 II. Bonding and activation of hydrogen on surface defect sites and clusters

The defects of MoS2 were investigated for activation of hydrogen using density functional theory by modeling the molybdenum disulfide monomer, small clusters, and edges in periodic structures. Attachment of H2 to the MoS2 molecule was studied in detail, and several structures were found by optimization methods. A dihydride with the hydrogen atoms far apart was determined to be most stable. In this configuration, the σ* orbital of the H2 mixes with the 4d orbitals of Mo and 3p orbitals of S to achieve the hydrogen activation. The less stable η2 hydrogen configuration has the H–H bond slightly stretched with the H atoms equidistant from the Mo center. A triangular Mo7S14 cluster provides a small model with edges resembling those of the cut MoS2 sheets. On this cluster, both the η2 hydrogen and the dihydride occur. periodic system, atomic hydrogen adsorbs in stable positions on the MoS2 edges either bridging between Mo atoms or attached to Mo or S atoms. The frequencies of H vibrations are found to be highly dependent on the atom(s) to which the hydrogen is attached, and range from 1223 cm−1 for a position bridging two Mo atoms, to about 1860 cm−1 for Mo–H bonds, to about 2500 cm−1 for S–H bonds. In addition, some configurations with molecular H2 adsorption on the edges were investigated, and the H–H frequency of 2999 cm−1 was calculated for a dihydride configuration.