Influence of Reduction / Sulfidation Treatments on the Physico‐Chemical and Catalytic Properties of Unsupported Cobalt‐Molybdenum/Hydrodesulfurization Catalysts

Abstract

AbstractUnsupported CoMo sulfide catalysts prepared by the homogeneous sulfide precipitation method were submitted to 3 MPa 4% H2S‐H2 at 573K, and 0.1 MPa H2 at 573 and 723K. The samples were characterized by MES, XPS, XRD and temperature‐programmed sulfur extraction. Their activity was measured in the HDS of thiophene and hydrogenation of cyclohexene. MES reveals the presence of Co9S8, CoS1+x, Co‐Mo‐S and two unidentified species. Treatment under H2 at 573K caused an increase of activity which was correlated with an increase of the Co9S8 concentration at the expense of all other species. Treatment under H2 at 723K caused a further increase of activity which was correlated with the sintering of the Co9S8 phase. Part of the sulfur extracted by treatment under H2 up to 733K cannot be recovered by subsequent treatment under H2S/H2. These results do not provide straightforward evidence for deciding between the current models used for explaining the synergetic effect, namely the existence of a Co‐Mo‐S phase or the remote control hypothesis. The sulfur deficiency of the catalyst appears to play a major role in the activity.