Influence of Sulfidation Temperature on the Dispersion and Activity of Cobalt‐Molybdenum Catalysts Supported on γ‐Alumina

A commercial cobalt‐molybdenum catalyst supported on γ‐alumina was activated by reduction‐sulfidation under 15% H₂S in H₂ in the temperature range 573 to 1073K. Optimum hydrodesulfurization activity was achieved after activation between 673 and 803K. At lower temperatures lower activity was observed and X‐ray photoelectron spectroscopy indicated that this was due to incomplete sulfidation of cobalt and molybdenum. Sintering of the supported phase, which occured after activation above 800K, was measured by high resolution electron microscopy, ion scattering spectroscopy and dynamic oxygen chemisorption. The hydrodesulfurization activity varied in the same proportion as the surface area of the MoS₂‐like crystallites. It was concluded that the number of active sites per unit surface area of supported phase and the intrinsic activity of these sites for hydrodesulfurization did not change during activation above 800K.