A practical approach to enhancing the performance of dispersed catalysts during slurry-phase hydrocracking is the modification of the ligand structure of the catalyst precursor. An oil-soluble Mo precursor with triphenylphosphine ligands (Mo-TPP) was prepared and further applied to the slurry-phase hydrocracking of vacuum residue (VR). For comparison, a commercial precursor termed Mo-octoate was also used. In a dispersibility test, Mo-TPP was completely dissolved at 200 degrees C and then finely dispersed in the VR. Thermogravimetric analysis revealed that Mo-TPP decomposed rapidly in the range 220-270 degrees C to produce zerovalent Mo. During the decomposition process, direct conversion of Mo-TPP to MoS2 was favored via reaction with H2S gas generated from the VR at 250 degrees C. The sulfidation behavior of Mo-TPP reduced the average size and stacking number of the resulting unsupported MoS2 catalyst, which led to greater exposure of the rim sites (Mo-rim) on the catalyst surface than when Mo-octoate was used. The Mo-TPP precursor resulted in better catalytic performance than the Mo-octoate precursor in a semibatch reactor at 410 degrees C and under 110 bar H-2. In particular, the use of Mo-TPP enhanced the radical scavenging and hydrodesulfurization activities, owing to excellent hydrogenation ability originating from the initial number of Mo-rim sites. The phosphate compound, derived from the TPP ligands, promoted the conversion of asphaltenes via demetallization of the intrinsic V species in the VR. These results demonstrated that Mo-TPP is an efficient precursor for achieving coke suppression that also improves product quality. (C) 2020 Elsevier Inc. All rights reserved.