Qiaoling Dai

TiO₂-Al₂O₃ supports with different incorporation methods of titania were synthesized via three methods: impregnation (TA-I), co-precipitation (TA-CP), and co-precipitation–hydrothermal treatment (TA-HT). And the NiMoP catalysts prepared on the corresponding supports were evaluated for hydrodesulfurization (HDS) reactions. The results demonstrated that the Ti atoms in TA-I are attached to alumina through hydroxyl groups, while the Ti atoms in TA-CP and TA-HT can be dispersed in the alumina skeleton. Variations in the incorporation modes of TiO₂ affect the support properties, consequently influencing the nature of the active metal on the supports. The Ti atoms dispersed in the Al₂O₃ skeleton allow an increase in the basic hydroxyl groups. Meanwhile, TiO₂ in TA-CP and TA-HT can absorb hydrogen molecules and be partially reduced. Furthermore, metal species supported on the TA-CP and TA-HT are more easily reduced and better dispersed. For the NiMoP catalysts prepared with TA-CP and TA-HT, the Ti element promotes the sulfidation degree of Mo, besides shortening the average (Ni)MoS₂ slab. The catalysts prepared with TA-CP exhibited superior activity for 4,6-DMDBT hydrodesulfurization. This can be ascribed not only to the relatively high sulfidation degree of Mo and proportion of the NiMoS active phase but also to the well-dispersed (Ni)MoS₂ slabs. Moreover, the Ti⁴⁺ ions dispersed in the Al₂O₃ skeleton can be partially reduced to act as electron donors, enhancing the metallic character of the S layers in MoS₂, which facilitates the improvement of the hydrogenation desulfurization activity.

In this present work, a new kind of sulfurized hydrodesulfurization catalyst was synthesized via the hydrothermal treatment of MoS₂, NiCO₃·2Ni(OH)₂·4H₂O, and Al₂O₃ precursors, followed by annealing under a H₂ atmosphere, which does not require a sulfurization process compared to traditional preparation methods. The influence of the annealing temperature and the type of Al₂O₃ precursor on the interactions between MoS₂ and Al₂O₃ were studied using X-ray fluorescence spectroscopy, X-ray diffraction, N₂ adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results indicated an increase in the number of stacked layers of the MoS₂ catalyst, accompanied by a decrease in the degree of decoration of Ni atoms onto MoS₂ nanoslabs, as a result of the strengthened MoS₂–Al₂O₃ interaction. Subsequently, the efficiency of hydrodesulfurization (HDS) was evaluated using dibenzothiophene as a representative reactant, while establishing a correlation between the structure of the catalyst and its performance. The catalysts, using pseudo-boehmite as the precursor and calcined at 500 °C, synthesized by calcining pseudo-boehmite as the precursor for Al₂O₃ at a temperature of 500 °C and possessing suitable metal–support interactions, exhibited a reduced number of MoS₂ stacking layers and lateral dimensions, along with an optimal decoration degree of Ni atoms, thereby resulting in the highest level of HDS activity.