The direct synthesis of methanethiol from H 2S-rich syngas was investigated over sulfided Mo-based catalysts supported on SiO 2. K-promoted Mo/SiO 2 catalysts exhibited a high activity for the synthesis of CH 3SH. The incorporation of cobalt into the K–Mo/SiO 2 catalyst increased the catalytic activity, but slightly decreased the selectivity to methanethiol. The selected catalysts were characterized by using X-ray diffraction (XRD), CO temperature-programmed desorption (CO-TPD), electron spin resonance (ESR), and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the potassium interacts with Mo component and increases the active sites for the CH 3SH synthesis by changing the concentration of Mo 5+ species after sulfidation. A mechanism for the synthesis of CH 3SH was proposed.