Hydrodesulfurization of thiophene on highly deactivated coal-liquid hydrotreatment catalyst: effect of deposited iron sulfide

Abstract

The hydrodesulfurization of thiophene was studied over highly deactivated NiMo on alumina catalysts, iron sulfide, and a combination of the two. Iron sulfide is one of the metals deposited along the periphery of the catalyst particle during deactivation. For the supported NiMo catalysts, the Arrhenius plots bend downward as temperature increases; i.e., the apparent activation energy decreases. This is as expected. However, at even higher temperatures, the plot for the highly deactivated NiMo catalyst bends upward again; i.e., the apparent activation energy increases. A two-step series reaction mechanism can be used to explain the results over the highly deactivated catalyst. Step 2 controls the reaction rate on NiMo catalysts, while on iron sulfide alone step 1 controls the rate. A model is presented describing diffusion and reaction within a catalyst pellet having a nonuniform activity distribution. The model predicts the Arrhenius plots obtained over deactivated catalysts, in particular, the increase in activation energy observed at high temperatures.