Effects of support on the activity of Co–Mo sulfide model catalysts

Abstract

The support effects of Co–Mo sulfide catalysts on the activities for hydrodesulfurization (HDS) and hydrogenation (HYD) were investigated by preparing model catalysts. CoS x –MoS 2 model catalysts were prepared by exposing supported Mo sulfide catalysts to a vapor of Co(CO) 3NO, followed by a second sulfidation. The supports used here were Al 2O 3, TiO 2, ZrO 2 and SiO 2. XPS results showed that the Co sulfide species interacting with MoS 2 particles are formed by using Co(CO) 3NO as a precursor. On the basis of a proportional correlation between Co/Mo and NO/Mo ratios, it is concluded that the Co sulfide species are located on the edge sites of MoS 2 particles, suggesting the formation of a CoMoS phase. The thiophene HDS activity was proportional to the amount of the Co species irrespective of the support for CoS x –MoS 2/Al 2O 3, TiO 2 and ZrO 2, indicating that the Co species form catalytically active sites and that no real support effects are observed in terms of the specific activity of the Co species. The higher activity of the Co sulfide phase supported on SiO 2 suggests that CoMoS(II) is formed on CoS x –MoS 2/SiO 2, whereas CoMoS(I) is formed on CoS x –MoS 2/Al 2O 3, TiO 2 and ZrO 2. On the other hand, the Co species on TiO 2, ZrO 2 and SiO 2 showed the identical specific activity for the HYD of butadiene. The Co species on Al 2O 3, however, exhibited a higher activity for HYD. The HDS and HYD reactions over the Co–Mo sulfide catalysts are affected by the support in different ways. The NO adsorption property of the CoS x –MoS 2 model catalyst was also examined.