Prior to the characterization of sulfided catalysts and the catalytic
activity tests, the NiMo catalysts were activated by ex situ
sulfidation in a U-shaped glass flow reactor at atmospheric pressure.
First, the sample was flushed in nitrogen flow and gradually
increased temperature up to 150 C. After it reached this temperature,
the flow was switched to the sulfidation mixture (15 vol.% of
H2S in H2) with a flow of 20 mL min1 and then the temperature
was increased to 400 C in ca. 1 h. The sulfidation continued under
these conditions for 4 h. Then the sample was cooled down to room
temperature, and the sulfidation mixture was changed to nitrogen
when the temperature decreased to 150 C. Freshly sulfided catalyst
samples were used for the catalytic activity tests and SEM–
EDX characterization. For HRTEM characterization, the sulfided
catalysts were kept in heptane.