H-2 interaction with S atoms of a MoS2 modelled catalytic site: Electronic density analysis for S-H formation

Semi-core effective core potential (ECP2) calculations were carried out for Mo3S6 and Mo2S6 clusters that modelled MoS2 catalyst surface sites (sulfur sites). The interaction of H-2 with monocoordinated (S-m) and bicoordinated (S-b) sulfur sites was studied. The topological properties of Mo-S bonds and the critical points (CP) of the charge density Laplacian (-del(2) rho(r(cp))), in the S valence shell, were analyzed. The results indicate that H-2 is dissociated over sites formed by two neighbor S atoms. The local interaction of H-2 with the S atoms occurs in the region in which there is the highest spin density concentration; i.e., the zone located at the CP maxima of -del(2) rho(spin)(r(cp)). This work shows the importance of calculating the CP of -del(2) rho(r(cp)) on the surface atoms to determinate active sites on a surface.