Elucidation of molybdenum-based catalysts using a radioisotope tracer method Part 2 Promotion effect of cobalt on molybdena/alumina catalyst

Description of coordinatively unsaturated sites regeneration over MoS2-based HDS catalysts using 35S experiments combined with computer simulations

“…We found a value of about 7.4 kcal.mol -1 , which is lower than that observed on non-promoted Mo/Al 2 O 3 catalysts (~ 10 kcal.mol -1 [74,88]). In contrast, the activation energy of the HDS reaction was about 23± 1 kcal.mol -1 whatever the Co loading [75,77], which is almost equivalent to the value observed on non-promoted catalysts (about 20 ~ 22 kcal.mol -1 ). This suggests that the addition of cobalt to the MoS 2 active phase might essentially not modify the activation energies of the reaction steps that are directly involved in the C-S bond breaking, but that it has an effect on the sulfur mobility.…”

“…Co and Mo in the HDS reaction might originate from the special mobility of sulfur atoms in such a configuration [75]. Then, computer simulations on the NiMoS phase will be performed by analogy to the simulations performed on the CoMoS phase, when the mechanism over CoMoS will have been unambiguously elucidated.…”

“…Besides, 35 S radioactive tracer methods were developed to determine the sulfidation process of HDS catalysts as well as to describe the HDS reaction mechanism over various catalysts under real working conditions [32,34,35,[73][74][75][76][77][78][79][80]. On the other hand, with the recent developments of the computer simulations, new insights in the state of the HDS catalysts surface [81][82][83][84] as well as an overview of the HDS mechanism over the simulated surfaces were concurrently proposed [85,86].…”

Deep Hydrodesulfurization of Light Gas Oil. (Part 2). Effect of Hydrogen Sulfide on Hydrodesulfurization of Dibenzothiophenes Included in Hydrotreated Light Gas Oil.

“…We have already reported in our studies using 35S that the catalyst sufficiently sulfided is not subject immediately to reduction even under H2 pressure, and that after H2 treatment for several hours, deactivation in HDS is not observed19), 20). From these facts, it is likely that the activity of HDS is maintained when gas oil with sulfur content higher than 0.05wt% is used.…”

Investigation of Sulfur Behavior on Mo-based Hydrodesulfurization Catalysts Supported on High Surface Area TiO₂ by ³⁵S Radioisotope Tracer Method

“…Therefore, the results indicate that the use of TiO2 as a support instead of Al2O3 mobilizes the sulfur on the sulfided Mo/TiO2 catalysts rather than inducing an increase in the number of active sites. In a recent study 36) , we proposed that the promoting effect of cobalt for Mo-based catalysts on an alumina support is due to increased mobility of the sulfur in the socalled "CoMoS" phase, in which we supposed that the strength of the Mo _ S bond was weakened. A structural model was accordingly built 37) .…”