Formation of η-Carbides by Mechanical Alloying of Co25Mo25C50 and Their Performance in Hydrodesulfurization

Cobalt–molybdenum η-carbides are attractive hydrodesulfurization (HDS) catalysts, yet controlling their phase composition and nanostructure remains challenging. Here, a Co25Mo25C50 powder was prepared by mechanical alloying in a horizontal mill, with and without superimposed vertical vibration. Phase composition was determined by X-ray diffraction using the reference-intensity-ratio method, and the nanostructure was examined by SEM and HRTEM. Aquathermolysis of a heavy crude was monitored by ATR-FTIR in the window characteristic of S–S and C–S vibrations. Both milling routes produced the η-carbides Co3Mo3C and Co6Mo6C, as well as Co2Mo3, Co7Mo6, and Co3C; vibration-assisted milling increased the Co6Mo6C fraction and generated thin lamellae exhibiting Moiré contrast. In FTIR, the Co6Mo6C-rich powder showed strong attenuation of the disulfide and thioether bands, whereas the Co3Mo3C-rich powder behaved similarly to the water-only baseline under mild conditions (100 °C, 4 h). These results indicate that mechanical alloying with superposed vibration enables control over phase and nanostructure, and that a higher Co6Mo6C fraction correlates with a stronger HDS response under aquathermolysis. The approach offers a scalable route to Co–Mo carbides that are active for desulfurization at 100 °C in water without added H2.