Electronic structure and reactivity of defect MoS2II.: 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 H-2 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 sigma* orbital of the H-2 mixes with the 4d orbitals of Mo and 3p orbitals of S to achieve the hydrogen activation. The less stable eta(2) 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 92 hydrogen and the dihydride occur. In the 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 1223cm(-1) for a position bridging two Mo atoms, to about 1860cm(-1) for Mo-H bonds, to about 2500cm(-1) for S-H bonds. In addition, some configurations with molecular H-2 adsorption on the edges were investigated, and the H-H frequency of 2999cm(-1) was calculated for a dihydride configuration. (C) 2004 Elsevier B.V. All rights reserved.