Effect of the support on the high activity of the (Ni)Mo/ZrO2–SBA-15 catalyst in the simultaneous hydrodesulfurization of DBT and 4,6-DMDBT

Series of Mo- and NiMo-catalysts were supported on ZrO2, Al2O3, SBA-15, and ZrO2-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 N2 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 MoS2 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 MoS2 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 ZrO2–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 MoS2-like clusters with short lengths. Thus, the NiMo/ZrO2–SBA-15 catalyst was able to convert DBT-type compounds with typical and low reactivity on the NiMo/Al2O3 catalyst.

The hydrodesulfurization of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) on Mo- and NiMo-catalysts supported on pure oxides and ZrO2–SBA-15 indicated that the active phase morphology was the dominant factor during the reaction. Monolayers of MoS2 in Mo catalysts had low activity for the HDS of both DBT compounds. On NiMo catalysts, DBT reacted on monolayered and stacked NiMoS clusters, but 4,6-DMDBT was converted only on the latter.Figure optionsDownload high-quality image (142 K)Download as PowerPoint slideHighlights
► The HDS of DBT and 4,6-DMDBT was studied on Mo and NiMo catalysts supported on ZrO2–SBA-15, ZrO2, Al2O3, and SBA-15.
► Characteristics of Mo oxide precursors determine the morphology of MoS2 and NiMoS clusters.
► Monolayers of MoS2 in Mo catalysts have low activity for HDS of both dibenzothiophenes.
► In the case of NiMo catalysts, DBT was able to transform on both monolayered and stacked NiMoS particles.
► The HDS of 4,6-DMDBT requires the presence of short but stacked NiMoS clusters as those obtained on ZrO2–SBA-15.