On the basis of the results from the Fr-IR, XRD and catalytic studies, a suggestion about the mechanism of surface transformations of Ni-supported detonation-synthesized ultradispersed diamond and the influence of these transformations on the state of the loaded metal have been made. It was proposed that in dependence on the inert or oxidative atmosphere applied for the elimination of the Ni salt precursor, different interactions of the support with the NiO species have taken place that determined the way of their coordination and stability as well as the dispersion of the metal nickel phase formed upon their reduction. The catalytic activity of the latter has been tested in the reaction of toluene hydrogenation. (c) 2007 Elsevier B.V. All rights reserved.