Correlation between electronic properties and hydrodesulfurization activity of 4d-transition-metal sulfides

The present study attempts to examine the relationship between electronic-structure properties exhibited by 4d-transition-metal sulfides (TMSs) in connection with the hydrodesulfurization (HDS) catalytic activity. The electronic structure is studied by means of a periodic density functional approach using a plane-wave basis set and appropriate pseudopotentials. Both bulk and relevant surfaces of NbS, NbS(2), MoS(2), TcS(2), RuS(2), Rh(2)S(3), PdS, and PdS(2) have been analyzed. High densities of nonbonding states below the Fermi level have been found for the TMSs that exhibit good catalytic performance. Therefore, it is suggested that the incomplete filling of the band gap at exposed transition metal atoms over the catalyst surface plays a determinant role in the HDS reactions. It has also been found that the highest HDS activity occurs when the surface-metal-site density of electronic states has a local minimum at the Fermi level that enhances the donation-back-donation mechanism. Additionally, the Sabatier principle is qualitatively rationalized in terms of the position of covalent bands below the Fermi level.