ELECTRONIC-STRUCTURE OF RH2S3 AND RUS2, 2 VERY ACTIVE HYDRODESULFURIZATION CATALYSTS

The results of Fenske-Hall band structure calculations for bulk Rh2S3 and RuS2 and for the (210) and (111) surfaces of RuS2 are described. A lthough the crystal structures of the two sulfides are quite different , the electronic structure of bulk Rh2S3 and RuS2 share several simila rities. Unlike MoS2, which is also used as a hydrodesulfurization (HDS ) catalyst, there is no metal-metal bonding and only negligible metal- sulfur rr bonding in both Rh2S3 and RuS2. As a result, both sulfides a re characterized by a narrow high energy occupied metal t(2g) band loc alized on the metal. Results of calculations for two-dimensional RuS2 slabs exposing (210) and (111) surface planes provide a description of the electronic structure of 5-, 4-, and 3-coordinate Ru atoms on thes e surfaces. Stabilization of part or all of the unoccupied Ru e(g) ban d is observed for these surface atoms, and comparisons between the par tial densities of states (DOS) of the surface Ru atoms and the orbital structures of isolated coordinatively unsaturated metal centers aid i n the interpretation of the surface results. The electronic environmen ts of the surface Ru atoms are also compared to the electronic environ ments and reactivities of metal centers found in d(6) transition metal complexes that incorporate thiophenic ligands. These comparisons sugg est that if the heterogeneous and homogeneous HDS mechanisms are relat ed, then 3-coordinate surface Ru atoms such as those found on the (111 ) surface could provide active sites.