Activity and thermal stability of sonochemically synthesized MoS2 and Ni-promoted MoS2 catalysts

Sonochemically synthesized MoS2/Al2O3, which had a hydrodesulfurization (HDS) activity that was significantly greater than that of a catalyst prepared by impregnation, exhibited low thermal stability due to sintering of MoS2 crystallites at high temperatures. The thermal stability was improved when the catalyst was promoted with Ni. In this study, we compared the activity and thermal stability of different Ni-promoted MoS2 catalysts, which were prepared by addition of Ni to MoS2 using either impregnation (IMP) or chemical vapor deposition (CVD). After use in the HDS of dibenzothiophene (DBT) at 673 K for 2 h, the initial activity of the un-promoted catalyst was partially lost, while that of the Ni-promoted catalysts was preserved. Ni added by CVD interacted more intimately with MoS2 than Ni added by impregnation because CVD allowed selective deposition of Ni on the MoS2 edge sites. Another advantage of the CVD method over the impregnation method is that Ni(CO)4, which was used as the Ni precursor in the former method, could be decomposed at much lower temperatures than in the case of Ni(NO3)2, which was used in the impregnation method. As a result, Ni-promoted catalysts prepared using Ni-CVD showed superior HDS activity compared with those prepared using Ni-impregnation.