Influence of the crystalline structure of Co-Mo precursors on the hydrodesulfurization performance of unsupported tube-like Co-Mo sulfide catalysts

A series of Co-Mo sulfide catalysts with tube-like hollow structure were prepared by a low temperature pre-sulfurization method using various CoMoO₄ as precursors synthesized by coprecipitation process at different temperature. The crystallite structure of CoMoO₄ precursors determined the properties of Co-Mo sulfide catalysts, including pore structure, concentration of CoMoS active phase, microstructure of MoS₂ slabs, and desulfurization activity. The higher temperature led to better crystallinity of CoMoO₄ precursor, resulting in less CoMoS active phase and fewer Mo atoms at the corner sites of the pre-sulfurized catalyst. In addition, the MoS₂ slabs with shorter length and more stacking layers (especially Co-promoted MoS₂ slabs) in the catalysts are also formed at appropriate precursor preparation temperature, which are favorable for forming more unsaturated coordination sites (especially corner sites). According to the results of hydrodesulfurization of dibenzothiophene on the Co-Mo sulfide catalysts, the reaction rate and the production yield are highly dependent on the number of surface-active centers, while the activity is mainly attributed to the Type II CoMoS species.