Molybdenum disulfide nanoparticles are of interest for their extensive use in heterogeneous catalysis. Here, we report a systematic density functional theory study carried out to investigate the electronic effects of Co(Ni) mono-substitutions on triangular molybdenum sulfide models of nanometric scale. On the basis of the electronic structure, the charge distribution and the Delta(E-LUMO - E-HOMO) gap analysis, the triangle molecular model with nickel substitution is identified as more favorable for inducing the best catalytic performance. Nickel consistently induces stronger electronic rearrangements than cobalt, on the molybdenum first-neighbor atoms, which are connected with its higher promoting effect. Charge distribution analysis points out a chemical reduction on the molybdenum sites when the cluster is doped. Moreover, nickel substitution produces smaller Delta(E-LUMO - E-HOMO) gaps than cobalt substitutions, revealing that Ni-doped clusters are more reactive. (C) 2009 Elsevier B.V. All rights reserved.