The effect of changing the sulfiding temperature (T-s) of a Go-Mo sulfide/gamma-Al2O3 hydrogenation catalyst in the range 200 degrees C to 450 degrees C, has been studied by the hydrogenation of cyclopentadiene, styrene alphamethylstyrene and indene impurities in a commercial plant feed at 200 degrees C in a laboratory reactor. Transmission electron microscopy (TEM) was used to examine the morphology and structure of the catalyst and X-ray photoelectron spectroscopy (XPS) to ascertain the oxidation states of the Co and Mo.The performance of the catalyst peaked for T-s around 400 degrees C. For T-s < 300 degrees C, the presence of catalyst material on the substrate could be deduced with TEM only from the grainy appearance of the support, but for higher T-s, MoS2 was seen arranged with its basal planes normal to the support. XPS revealed increased concentrations of Mo4+, as MoS2, with rising T-s. The Co 2p(3/2)-S 2p binding energy splitting increased from 616.0 +/- 0.2 eV at T-s = 200 degrees C to 617.3 +/- 0.1 eV at T-s = 350 degrees C, indicating that the Co increasingly decorated the edges of the MoS2.