Washing with xylene (X), 2,6 bis 1 hydroxy 1,1 diphenyl methyl pyridine (A) and in situ reactivation with molybdenum acetylacetonate (AceMo) on the NiMoP/Al2O3 spent surface catalyst has been investigated in the hydrodesulfurization (HDS) of straight-run gas oil. The spent catalyst was washed and dried at 120 °C before in situ reactivation. The sulfided catalysts were characterized by temperature programmed reduction (TPR), nuclear magnetic resonance (NMR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The HDS reactions were carried out at 5.5 MPa of H2 and the reaction temperatures at 340 °C, 360 °C and 380 °C. The CatAXAceMo displayed the highest HDS activity. The TPR results advice that CatAX presented more “rigid” MoS2 edges than CatRef catalyst. NMR results suggest that CatAXAceMo showed lower aromatic or polyaromatic hydrocarbons surface concentration deposited after HDS reaction than CatAceMo and CatRef. Raman spectroscopy revealed the formation of coke crystallites with shorter size for CatAXAceMo than others catalysts. XPS spectroscopy results exhibited that CatAXAceMo presented smaller superficial carbon and a larger concentration of MoS2 active phase. A relation between the coke crystallites size and MoS2 superficial concentration was found. A lower aromatic concentration favors the shorter coke crystallites sizes and a major availability of Mo species for the formation of MoS2 to HDS reaction.