Nickel (Ni) and nickel molybdate (NiMo) supported on alumina (Al2O3) catalysts, both in a presulphided and prereduced forms, were investigated for the hydrogenation (HYD) of naphthalene. The deactivation of the catalysts with time on stream and sulphur (S) content in feed was studied and a detailed characterization of the catalysts was performed. The catalytic activity of the presulphided NiMo/Al2O3 catalyst was found to be 2.5 times higher than the prereduced form, at the same HYD conditions. Testing the commercial prereduced Ni catalyst, it was observed that, although the catalyst aged quite quickly, it gave a higher turnover frequency at a temperature that was significantly lower than the one needed for the presulphided NiMo/Al2O3 catalyst. The presulphided Ni/Al2O3 catalyst showed a low activity towards naphthalene HYD, for the same experimental conditions applied to the prereduced form. The presulphided form of this catalyst was not the active site for this HYD. The Ni catalyst should be used in a sulphur free environment in order to fully make use its hydrodearomatisation (HDA) properties, whereas the NiMo/Al2O3 catalyst exhibited a higher HYD activity in the presulphided form. (C) 2007 Elsevier B.V. All rights reserved.