MoS2/Al2O3 catalysts were prepared by a simultaneous impregnation method with citric acid as chelating agent in order to investigate the effect of high pressure sulfidation on the morphology and reactivity of MoS2 slabs by infrared spectroscopy of CO adsorption (IR/CO), transmission electron microscopy, thiophene hydrodesulfurization (HDS) and 2,6-dimethylaniline hydrodenitrogenation (HDN) reactions. It is found that the MoS2 slabs are more truncated when sulfided at higher pressure, exposing larger S-edge/M-edge ratio. The thiophene HDS activity of MoS2/Al2O3 catalysts was significantly improved by high pressure sulfidation. The MoS2 edges formed after high pressure sulfidation are very stable toward H-2-treatment, while the same H-2-treatment can create sulfur vacancies on both M-edge and S-edge of the 0.1 MPa sulfided MoS2 slabs. Meanwhile, parallel between the IR/CO results and HDN test suggests that the S-edge favors the C-N bond scission whereas the M-edge benefits the hydrogenation in HDN reaction. (C) 2016 Elsevier Inc. All rights reserved.