Effect of the support composition on the characteristics of NiMo and CoMo/(Zr)SBA-15 catalysts and their performance in deep hydrodesulfurization

Abstract

In the present work, we tried to get a deeper insight into the effect of the chemical composition of the SBA-15-type support on the development of NiMo and CoMo catalysts in deep hydrodesulfurization (HDS). With this aim, two series of catalysts were prepared using pure silica SBA-15 and ZrO 2-containing SBA-15 as supports. Supports and catalysts were characterized by nitrogen physisorption, small-angle and powder XRD, TPR, UV–vis DRS, HRTEM, and tested in the simultaneous HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). It was found that the nickel promoter significantly decreased the temperature of reduction of Mo oxide species on both supports used, while the effect of cobalt was relatively small. TPR profiles of Ni/SBA-15 and Co/SBA-15 samples exhibit much smaller metal–support interaction for Co than for Ni. In addition, the presence of agglomerated β-CoMoO 4 phase was detected in the XRD pattern of the CoMo/SBA-15 catalyst, whereas the formation of this phase was avoided in the CoMo/ZrSBA-15 sample. TPR results show that zirconia incorporation on the SBA-15 surface significantly increases Co–support interaction and, consequently, the promoter dispersion leading to a better promotion of the MoS 2 active phase. In line with the characterization results, catalytic activity of NiMo catalysts was much higher than those of Mo or CoMo counterparts. In addition, the behavior of Co-promoted Mo/(Zr)SBA-15 catalysts was strongly affected by the chemical composition of the support used, especially in hydrodesulfurization of sterically hindered 4,6-DMDBT. HRTEM study was undertaken to establish how the nature of the promoter as well as the support composition affected the morphology of the active MoS 2 phase and influenced its catalytic behavior.