Molecular sulfide clusters with bimetallic Mo3S4M' cluster cores (M' = Ru, Rh,Ir, Pd, Pt) were impregnated on gamma-alumina as the compounds [(Cp')(3)Mo3S4M'(L)(x)][IPts](y) (Cp' = methylcyclopentadienyl; L=ligand; pts=para-toluenesulfonate). These catalyst precursors were sulfided at 350 degrees C leading to decomposition of the molecular clusters and the formation of MoS2-like phases with optimal chances for noble metal atoms to be in close contact with MoS2. The hydrotreating activities of the catalysts obtained were measured by using a feed containing dibenzothiophene, indole and naphthalene. The HDS, HDN and HYD activities followed the order Mo3Ir > Mo3Rh > Mo3Ru > Mo3Pt > Mo3Pd. Comparison with the sum of activities of a monometallic Mo and a monometallic noble metal reference catalyst revealed strong synergies for the Mo3Ir and Mo3Rh catalysts, whose HDS and HDN activities had increased by factors of 2.7-3.9 and 1.8-4.3, respectively. A comparison with the hydrotreating activities of a Mo3Ni catalyst prepared from [(Cp')(3)Mo3S4NiL][pts] showed, however, that the performances of the Mo3Rh and Mo3Ir catalysts generally were inferior by a factor of 2 to a Mo3Ni catalyst. An inhibiting effect on the catalyst activity was observed for the Mo3Pd catalyst. The sulfided Mo3Rh. Mo3Ir and Mo3Pd catalysts were studied by TEM. The Mo3Rh and Mo3Ir catalysts showed a homogeneous and very high dispersion of both metals, the MoS2 dispersion being higher than in the monometallic Mo reference catalyst. The Mo3Pd catalyst showed a strong inhomogeneity due to the presence of 10 nm large Pd4S particles fully encapsulated by layers of MoS2. (C) 2010 Elsevier B.V. All rights reserved.