The effect of the nature of sulphur compounds (H2S and 2-methylthiophene) over unsupported molybdenum-based sulphide catalysts (promoted or not by nickel or cobalt) for the transformation of a model FCC feed (hydrodesulphurisation of 2-methylthiophene and hydrogenation of 2,3-dimethylbut-2-ene) was investigated. The activities of the various catalysts were compared between each reactant alone and the full model mixture. The promoting effect of Co and Ni is found for both hydrodesulphurisation (HDS) and hydrogenation of olefins (HYD) reactions. However, the hydrogenation activity strongly depends on the amount of sulphur compound present in the feed. Nickel, used as a promoter, seems more sensitive than cobalt, particularly for the hydrogenation reaction. The presence of 2-methylthiophene in the feed induces a stronger inhibiting effect than H2S on HYD reaction. This result highlights the different adsorption constant ratio between olefins and sulphur molecules depending on the sulphur compounds. Even though an impact of H2S can be observed on the NiMo and CoMo catalysts, no major modification occurs on the volcano-shaped curves obtained in previous work, in terms of activity or selectivity, as a function of the metal-sulphur bond energy. Whatever the amount of H2S added, NiMo and CoMo catalysts fit into the curve. NiMo being the most active and the most selective under these conditions. (C) 2010 Elsevier B.V. All rights reserved.