Description of coordinatively unsaturated sites regeneration over MoS 2-based HDS catalysts using 35S experiments combined with computer simulations

Abstract

By combining experimental results and computer simulations, we previously showed that the coordinatively unsaturated sites (CUS) formation over MoS 2 is most likely to occur on the MoS 2 metallic edge through the departure of an H 2S molecule. In the present paper, we aimed at examining the H 2S departure from MoS 2 catalysts promoted with Co and Ni. The [ 35S]DBT HDS experiments results showed that over CoMoS/Al 2O 3 and NiMoS/Al 2O 3 catalysts, the activation energy of the H 2S release reaction is essentially the same with respective values of 7.4 and 7.9 kcal mol −1. Considering the H 2S departure activation energy in the case of the non-promoted MoS 2 surface (10–12 kcal mol −1), this result illustrates the synergetic effect between Mo and Co or Ni in terms of CUS regeneration easiness. Further, preliminary computer simulations results showed that for S atoms bridged between Co atoms, a mechanism implying H 2S departure from the metallic edge cannot be reasonably envisaged. Moreover, on the sulfur edge the H 2S release activation energy is too high (∼13.5 kcal mol −1) if we consider experimental results on CoMo/Al 2O 3 catalysts, but not incompatible with the experimental value obtained over Co/Al 2O 3 catalysts (ca. 10 kcal mol −1), which suggests that the mechanism on the promoted catalysts differs from that on the un-promoted ones.