Abstract
The deactivation and modeling of 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 was expressed by an equation on the basis of two types of active sites 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 constant for easily deactivated sites and sites deactivated with difficulty, respectively. The former sites were based on the Elovich kinetics which represented the initial deactivation caused by sulfur accumulation and nitrogen release. The latter sites were based on first order deactivation kinetics in the intermediate stage of the reaction. The catalyst lifetime of the 973K-nitrided catalyst was 2.3, 24.8 and 44.5 times longer than those of the 773 K- and 1173 K-nitrided and 623 K-sulfided catalysts, respectively, at a conversion of 10%. The behavior of nitrogen release, carbon deposition, and sulfidation was determined by XPS and related to the deactivation parameters.
