Regeneration of a Deactivated Hydrotreating Catalyst

A commercial NiMo/Al2O3 catalyst deactivated in a shale oil hydrogenation plant was submitted to several regeneration procedures. The results show that direct coke burnoff with an oxidizing mixture containing low oxygen levels (1.6% v/v O2) was more efficient in recovering the catalytic activity and the textural properties of the spent catalyst than reductive treatments (5% v/v H2) or sequential treatments of solvent extraction with acetone or cyclohexane/regeneration. Diffuse reflectance spectroscopy results suggest that, after the regeneration step, there was some nickel promoter loss due to nickel spinel (NiAl2O4) formation. The spinel formation explains why the catalytic activity of the fresh catalyst was not fully recovered after the regeneration of the spent catalyst, and its formation might be attributed to an unobserved temperature increase in the catalytic bed during the carbon burnoff step.