A simple two-step method to synthesize the well-ordered mesoporous composite Ti-FDU-12 and its application in the hydrodesulfurization of DBT and 4,6-DMDBT

Abstract

Mesoporous FDU-12 silicas with different morphologies have been synthesized under static and stirring conditions in a water bath. Furthermore, a series of mesoporous FDU-12 silicas modified by different amounts of titania have been synthesized, through a two-step method of prehydrolysis of TEOS followed by addition of titanium butoxide as a titanium precursor. Their respective NiMo supported catalysts were also prepared and characterized to elucidate the effects of titania, on the characteristics of the Mo surface species and their hydrodesulfurization (HDS) activities on dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The composites were characterized by various techniques (XRD, SEM, TEM, FT-IR, UV-vis, ²⁹Si NMR, Raman, XPS and N₂ adsorption–desorption); meanwhile, the catalysts were also tested in a higher pressure HDS reactor at T = 340 °C and P = 4 MPa with different liquid hourly space velocity (LHSV) values. The results show that the two-step synthetic route can prepare well-ordered mesoporous composites with high surface areas and large pore sizes and volumes. Obvious differences in the Mo species can be observed on the sulfided NiMo/Ti-FDU-12 catalysts. This showed that appropriate Ti loading could facilitate the dispersion of molybdena and the formation of the MoS₂ and NiMoS phases, which are the important factors for the HDS reaction. All of the catalysts presented high HDS activity, and when the Si : Ti molar ratio was increased to 5, the HDS activities on DBT and 4,6-DMDBT could reach as high as 97% and 65% respectively.