Towards the characterization of active phase of (Co)Mo sulfide catalysts under reaction conditions—Parallel between IR spectroscopy, HDS and HDN tests

A series of sulfided (Co)Mo/Al catalysts was examined using IR spectroscopy of CO adsorption (Tads ∼ 100 K), thiophene hydrodesulfurization and 2,6-dimethylaniline hydrodenitrogenation. Spectroscopic analysis after treatments at H2S partial pressures and temperatures close to the working conditions allows one to establish relationship between the nature, environment and concentration of sulfide phase sites and their catalytic functionalities. Unpromoted and Co-promoted edge sites do not exhibit the same sensitivity towards change in H2S/H2 partial pressure ratio. The Mo sites created in low H2S/H2 conditions present functionalities different from those formed in sulfiding conditions. By contrast, the Co-promoted sites are easily created even in sulfiding conditions and the sites generated in high or low H2S/H2 conditions possess the same environment as well as the same reactivity. Note that CoMo catalysts prepared by classical impregnation always exhibit an incomplete promotion of the MoS2 slabs even when containing high Co/Co + Mo ratio.