Size-dependent activity of unsupported Co–Mo sulfide catalysts for the hydrodesulfurization of dibenzothiophene

• The particle size of CoMoO4 precursors can be adjusted by changing alcohol–water solvent.
• The HDS activity of finial Co–Mo sulfides is closely related to their particle size.
• Small particles benefit the exposure of active sites, improving the conversion of DBT.

A series of CoMoO4 hydrates composed of nanorods have been synthesized with different alcohol–water solvent systems, and the corresponding Co–Mo sulfides are obtained after sequential calcination and sulfurization. The characterization results show the change in solvent system can efficiently adjust the particle size of the Co–Mo precursors, while cannot affect their components and morphologies. Because of the different particle size, the specific surface areas (SSA) of the final Co–Mo sulfides are different. The particles with small size can lead to a high SSA that benefits the exposure and dispersion of active components, and further promote the incorporation of MoS2 slabs with Co atoms to form “Co–Mo–S” structures on the surface of the sulfides. More “Co–Mo–S” structures would create more coordinative unsaturated sites with high activity in situ during hydrodesulfurization (HDS) reaction, resulting in a higher HDS activity. Among the Co–Mo sulfides, since S-m/w derived from methanol–water system possesses the smallest particle size and the most active sites, it naturally exhibits the highest HDS activity toward dibenzothiophene.

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