Synthesis of novel NiMo catalysts supported on highly ordered TiO2-Al2O3 composites and their superior catalytic performance for 4,6-dimethyldibenzothiophene hydrodesulfurization

Highly ordered mesoporous TiO2-Al2O3 composites with different TiO2 mass contents (MA-xTi) were successfully synthesized via an improved solvent evaporation-induced self-assembly method and the corresponding NiMo supported hydrodesulfurization (HDS) catalysts were prepared via wetness incipient co-impregnation method. The materials were characterized by means of XRD, ICP-OES, N-2 physical adsorption-desorption, SEM, TEM, PyFTIR, H-2-TPR, HRTEM and XPS and the catalytic activities for 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS over the prepared NiMo/MA-xTi series catalysts were investigated. The results show that the crystal forms, crystal morphologies, pore structures, pore arrangements and acidity properties of the MA-xTi samples varied with the incorporation and increase of TiO2 species; the interaction between the active metals and the support materials (MSI) can be modulated by the incorporation of TiO2 species, and TiO2 incorporation also can promote the formation of the so-called Type II NiMoS active phase via changing the morphology of Ni promoted MoS2 slabs, promoting the sulfidation of both Ni and Mo species and enhancing the proportion of NiMoS phase. The catalytic evaluation results show that the enhancement in the overall HDS activity of the NiMo/MA-xTi series catalysts were mainly contributed by the enhancement in the hydrogenation desulfurization (HYDS) activity. Catalyst NiMo/MA-20Ti exhibited the superior catalytic performance due to its highly ordered mesopore arrangement, proper acidity, moderate MSI, moderate stacking and high proportion of NiMoS phase which leads to more highly active Type II active sites.