Effect of the support on the high activity of the (Ni)Mo/ZrO _2-SBA-15 catalyst in the simultaneous hydrodesulfurization of DBT and 4,6-DMDBT

摘要

Series of Mo- and NiMo-catalysts were supported on ZrO_2, Al _2O_3, SBA-15, and ZrO_2-modified SBA-15 and tested in the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The rate constants of the main steps in the HDS reaction network of both molecules were calculated, and the materials were characterized by N_2 physisorption, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, temperature-programmed reduction and sulfidation, NO adsorption and high-resolution transmission electron microscopy. Tetrahedral and octahedral Mo species in the oxide precursors were related to the monolayers and multilayered MoS_2 structures, respectively, in the sulfide catalysts. The morphology of the active phase and the formation of the NiMoS phase were the most important factors during the HDS process of DBT-type compounds given that the turnover frequency values did not depend on the support composition or the morphology of the active phase. The monolayers of MoS _2 had low activity for the HDS of both molecules on the unpromoted catalysts, whereas on the NiMo catalysts, DBT reacted on monolayers and stacked NiMoS clusters but 4,6-DMDBT was converted only on the later structures. The optimum active phase-support interaction strength on ZrO_2-SBA-15 materials led to the characteristics of the active phase that maximized the total active surface and the active surface not sterically hindered by the support, i.e., stacked MoS_2-like clusters with short lengths. Thus, the NiMo/ZrO_2-SBA-15 catalyst was able to convert DBT-type compounds with typical and low reactivity on the NiMo/Al_2O_3 catalyst.