Nickel was impregnated in two Nb2O5/SiO2 samples. The first one contained small crystallites of niobia dispersed over silica and the second one a niobia monolayer distributed quite uniformly over the silica substrate. These systems were submitted to different treatments (calcination and water vapor) in order to obtain different interactions between the nickel and niobia. A preferential interaction of the nickel with niobia was observed in both niobia-silica Samples. The hydrogenation of benzene and dehydrogenation of cyclohexane were used to characterize the reduced surface nickel. Suppression in the catalytic activity was observed due to a strong metal-support interaction (SMSI) and nickel niobate formation. The extension of SMSI and nickel niobate formation depend on the niobia-silica interactions, which are a function of sample preparation and treatment. (C)2000 Elsevier Science B.V. All rights reserved.