Surface science models for CoMo hydrodesulfurization catalysts: Influence of the support on hydrodesulfurization activity

Flat model systems of supported oxidic CoMo hydrodesulfurization (HDS) catalysts, consisting of a conducting substrate with a thin SiO 2 or Al 2 O 3 layer on top of which the active catalytic phase is deposited by spin coating, were used to study the influence of the support and the use of chelating agents on the formation of the active CoMoS phase. On Co / Al 2 O 3 catalysts Co can only be partially sulfided due to the strong interaction with Al 2 O 3 . In the mixed phase CoMo / Al 2 O 3 system, the presence of Mo facilitates the sulfidation of Co. Due to the interaction of Mo with the support the Co–Al 2 O 3 interaction is blocked. In these catalysts the sulfidation of Co and Mo proceed at the same rate. In the case of CoMo / SiO 2 catalysts the weak interaction with the SiO 2 support results in the complete sulfidation of Co at low temperatures, while Mo sulfides at a slower rate. Thiophene HDS activity measurements showed that due to the stronger interaction, Al 2 O 3 is a better support for CoMoS formation. By complexing CoMo on Al 2 O 3 to chelating agents, like ethylenediaminetetraacetic acid (EDTA), the sulfidation of Co is retarded while that of Mo is facilitated. Although Mo also forms complexes with EDTA, these complexes are less stable than those of Co. Hence, the sulfidation of Mo precedes that of Co. Due to the absence of interaction with the support of the same sulfidation behavior was observed for both supports. The activity tests showed that these catalysts have the highest activity, irrespective of support.