Promotional effect of Co or Ni impurity in the catalytic activity of MoS2:An electronic structure study

It has been observed that the catalytic activity of MoS2 crystals is enhanc ed when either Co or Ni atoms are added. The presence of these atoms leads to electronic rearrangements, which are;considered the source of catalytic improvement. However, the relation between the electronic properties and th e enhancement of the catalytic activity is not yet fully understood. In ord er to get insight into the electronic-level changes that affect the catalys t performance, a solid-state density functional study has been carried out for Mo, Co/Mo, and Ni/Mo sulfides, using bulk and surface models. The MoS2 crystallize in a well-known layered,structure, which has been used together with the supercell model to simulate the (1 0 (1) over bar 0) edge surface of MoS2. The binary sulfides were obtained substituting Co or Ni by Mo fro m the original MoS2 bulk model. The electronic structure in a nonmagnetic s tate is analyzed and, in particular, the density of states of metal and sul fur atoms for the surface and bulk are compared. Finally, we discuss the im portant role that these properties play in the hydrodesulfurization reactio n and concluded that Mo at the surface remains the relevant reactive atomic center in the bimetallic systems, whereas Co and Ni are responsible for in creasing the Mo reactivity at the surface. (C) 2000 John Wiley & Sons, Inc.