Unblocking of NiMo Active Sites for Hydrodesulfurization Catalysts: A Study Focused on Inactive NixSy Segregation

The formation of NixSy/CoxSy phases on the HDS catalyst surface during catalyst preparation poses the following challenges in the HDS reaction: (1) inactive in the reaction, (2) hinder the role of promoters, (3) block the actives sites (NiMoS/CoMoS) at the perimeter, and (4) increase the inert mass on the catalyst surface. Since the formation of NixSy/CoxSy phases is thermodynamically favorable, it is difficult to control this during the catalyst synthesis. In this regard, this work investigates the effect of metal-support interactions and catalyst compositions on NixSy phase separation and removal of NixSy phases from the catalyst surface using acid-leaching method. The HDS activity for NiMo supported on amorphous alumina (NiMo/A-Al2O3) catalysts significantly increased after the acid-leaching treatment by unblocking the active NiMoS sites and increasing the Ni-MoS2 interaction through alumina support leaching. Overall, the HDS activity for leached NiMo/A-Al2O3 catalysts is 25–30% higher than that for conventional NiMo/γ-Al2O3 catalysts.