Abstract
The deactivation and modeling of the nitrided and sulfided 12.5 wt% MoO3/Al2O3 catalysts were studied during the hydrodesulfurization of dibenzothiophene at 573 K and a total pressure of 10.1 MPa. The deactivation behavior of the nitrided catalysts was expressed by an equation based on two types of active species, one of which was quickly deactivated and the other deactivated with difficulty: Φ = 1 – k1ln(t + α1) + k2exp(–α2t), where α1 and α2 are the first order rate constants for the easily deactivated species and the species deactivated with difficulty, respectively. The former species were based on the Elovich kinetics which represented the initial deactivation caused by sulfidation. The latter species were based on the first order deactivation kinetics during the intermediate stage of the reaction and deactivated by nitrogen release. The behavior of the nitrogen release, sulfidation, and carbon deposition was determined by XPS and related to the deactivation parameters of the equation. The catalyst lifetime of the 973-K-nitrided catalyst was estimated to be 2.3 and 24.8 times longer than those of the 773-K- and 1173-K-nitrided catalysts, respectively, at a conversion of 10%. For the sulfided catalyst, the initial deactivation of the sulfided Mo/Al2O3 catalyst was caused by sulfur poisoning during the dibenzothiophene HDS and by sulfur release in the intermediate stage.
