Preparation and Characterization of SBA-15 Supported Cobalt–Molybdenum Sulfide Catalysts for HDS Reaction: An All Sulfide Route to Hydrodesulfurization Catalysts

Abstract

MoS2 hydrodesulfurization (HDS) catalysts promoted with Co supported on SBA-15 were synthesized from sulfur-containing Mo sources [ammonium thiomolybdate (ATM), and tetramethylammonium thiomolybdate (TMATM)] and Co complexes cobalt dimethylthiocarbamate by using different synthesis strategies in order to achieve active catalysts. The (Co)-MoS2/SBA-15 catalysts were characterized with X-ray diffraction, N2-physisorption and High-Resolution Transmission Electron Microscopy. The catalytic performance in the HDS reaction of dibenzothiophene was examined at T = 623 K and P H2 = 3.4 MPa. The results of the experiments suggest that the sequence of impregnation steps has no significant influence on the HDS activity. On the other hand, the use of different thiomolybdate precursors significantly affects the catalytic activity. The catalysts derived from TMATM show lower HDS activities compared to the catalysts synthesized from ATM which is probably due to the presence of pronounced pore blocking as well as the generation of big needle-like aggregates of the Co–MoS2 phase. It seems that the formation of intermediate MoS3 is not a prerequisite for the generation of catalytic active CoMoS phases. The high activity and high selectivity for the direct desulfurization pathway of catalysts prepared with ATM despite the large MoS2 stacking could be due to the generation of a large number of coordinately unsaturated sites. Cobalt promoted molybdenum sulfide catalysts supported on mesoporous SBA-15 were prepared by an all sulfide route using sulfur-containing Mo and Co complexes. High catalytic activity at high Mo loading is observed for Co–MoS2/SBA-15 catalysts derived from ammonium thiomolybdate despite a pronounced stacking of MoS2 slabs. The catalysts prepared with tetramethylammonium thiomolybdate show lower HDS activities probably due to a pronounced pore blocking as well as the generation of big needle-like aggregates of the Co–MoS2 phase. The sequence of impregnation steps has no significant influence on the HDS activity. It seems that the occurrence of intermediate MoS3 is not necessary for the generation of catalytic active Co–MoS phases.