Synthesis of unsupported Co-Mo hydrodesulfurization catalysts with ethanol-water mixed solvent: Effects of the ethanol/water ratio on active phase composition, morphology and activity

Co-Mo sulfide catalysts with different particle size and structures were prepared in ethanol-water mixed solvent followed by a low-temperature sulfurization process, and were tested in dibenzothiophene hydrodesulfurization. The effects of the ethanol/water ratio on the particle size of precursors, active phase composition, active site number, morphology, and hydrodesulfurization activity of the final catalysts were investigated. The atomic ratio of Co/Mo and active phase morphology of catalysts closely relate to the dielectric constant of ethanol-water mixed solvent. Appropriate dielectric constant favors the formation of (Co)MoS(2)d slabs with shorter length (similar to 5.0 nm) and higher stacking number (similar to 4.3 layers), resulting in more coordinatively unsaturated sites, especially in the corner sites. The catalytic activity not only depends on the active sites of CoMoS phase, but also on that of Co9S8 and MoS2 phases because of synergistic effect. For MoS2 and CoMoS phases, the corner sites show higher direct desulfurization activity than the edge sites.