Evaluation of the maximum potential activity of Co–Mo/Al2O3 catalysts for hydrodesulfurization

Hydrodesulfurization Activity of Co–Mo/Al₂O₃ Catalysts Prepared with Citric Acid: Post-treatment of Calcined Catalysts with High Mo Loading

“…The activity of CoMo/ Al (calc) was increased by CVD ( 4 wt% Co). However, the activity of Co/CoMo/Al (calc) sharply decreased below 4 wt% Co, suggesting that the active sites are significantly masked by the catalytically inactive Co sulfide clusters 22) . The rate constant of CoMo/Al (calc) was slightly higher than that of the corresponding CoMo/Al (dried) catalysts (Fig.…”

“…Moreover, the sharp activity decrease of Co/CoMo/Al (dried) with increasing Co content is ascribed to blocking of the MoS2 sites by catalytically inactive Co sulfide clusters during the sulfidation process 22) . The rate constant of CoMo _ CA/Al was also considerably increased by the addition of Co using CVD at a low loading of Co (up to 6 wt% Co), suggesting that the edges of MoS2 particles in CoMo _ CA/Al are only partially occupied by Co at 6 wt% Co 22) .…”

“…Moreover, the sharp activity decrease of Co/CoMo/Al (dried) with increasing Co content is ascribed to blocking of the MoS2 sites by catalytically inactive Co sulfide clusters during the sulfidation process 22) . The rate constant of CoMo _ CA/Al was also considerably increased by the addition of Co using CVD at a low loading of Co (up to 6 wt% Co), suggesting that the edges of MoS2 particles in CoMo _ CA/Al are only partially occupied by Co at 6 wt% Co 22) . No activity increase after CVD was observed at a higher Co loading, possibly because the MoS2 edge sites are already fully covered by Co at 6 wt% Co 22) , although the MoS2 edges and thus Co _ Mo _ S are slightly blocked by catalytically inactive Co sulfides.…”

“…The prepared catalysts were sulfided in a 10% H2S/ H2 flow at 673 K for 2 h. The sulfidation procedures were described previously 17), 18) . A CVD technique using Co(CO)3NO as a precursor was applied to introduce Co into the sulfided catalyst 17),18), 22) . Briefly, the sulfided catalyst was first evacuated at 673 K for 1 h and subsequently exposed for 5 min at room temperature to Co(CO)3NO vapor at 273 K. After 10 min evacuation at room temperature, the sample was sulfided again at 673 K for 1.5 h. The prepared catalyst is designated as, for example, Co/Mo _ CA/Al, for the Mo _ CA/Al catalyst subjected to the CVD technique.…”

“…The rate constant of CoMo _ CA/Al was also considerably increased by the addition of Co using CVD at a low loading of Co (up to 6 wt% Co), suggesting that the edges of MoS2 particles in CoMo _ CA/Al are only partially occupied by Co at 6 wt% Co 22) . No activity increase after CVD was observed at a higher Co loading, possibly because the MoS2 edge sites are already fully covered by Co at 6 wt% Co 22) , although the MoS2 edges and thus Co _ Mo _ S are slightly blocked by catalytically inactive Co sulfides. On the other hand, the HDS activity of Co/CoMo _ CA/Al was constant below 6 wt% Co, indicating no notable active site blocking in CoMo _ CA/Al at 6 wt% Co. Figure 8 also shows that the rate constants of CoMo/Al (dried) and CoMo _ CA/Al at 0 wt% Co were very similar after CVD, suggesting that the edge dispersion of MoS2 particles was not modified by the addition of citric acid by the simultaneous impregnation method, in agreement with the amount of NO adsorption in Fig.…”