Deactivation study on nitrided molybdena–alumina during hydrodesulfurization of dibenzothiophene by X-ray photoelectron spectroscopy

The deactivation of 12.5% Mo/Al2O3 catalysts nitrided at various temperatures during the hydrodesulfurization (HDS) of dibenzothiophene at a 10.1 MPa total pressure was studied on the basis of a simulation using the kinetic equation and the behavior of nitrogen release (N/Mo atomic ratio), sulfidation (S/Mo), and carbon deposition (C/Mo) by X-ray photoelectron spectroscopy (XPS). The nitrided catalysts were deactivated in two regions where the activity significantly decreased up to 3 h and then very slowly in the period of 3–14 h. The catalyst deactivation during dibenzothiophene HDS followed the equation: Φ=r1 exp(−α1t)+r2 exp(−α2t), where r and α are constants, subscripts 1 and 2 denote the rapid and slow deactivation species, respectively, and t is the time-on-stream. The rapid initial deactivation (α1) was mainly attributed to carbon deposition on the surface, while the slow deactivation (α2) was significantly associated with nitrogen release. The highly nitrided Mo/Al2O3 catalyst (nitriding at 973 K) exhibited the least deactivation and longest catalyst lifetime.