The effects of loading and different nickel precursor compounds on the catalytic properties of unsupported and silica-supported Ni or NiO systems have been investigated. The extent of loading was varied between 5 and 20 wt.% metallic nickel or nickel oxide. The techniques employed for characterization of different solids were XRD, ESR, TEM and H2O2 decomposition at 30-50 degrees C. The results obtained indicated that the investigated catalysts contain clusters or very small particles of Ni or NiO phase. However, Ni or NiO catalysts based on nickel nitrate exhibited higher catalytic activities than the other two catalysts derived from nickel chloride and sulphate salts due to diminution of their particle size. In addition, the catalytic activities of SiO2-supported Ni or NiO catalysts were found to decrease as a function of extent of loading. The measurements of activation energy of the catalytic reaction of silica-supported catalysts containing different amounts of Ni or NiO revealed that the loading process did not modify the energetic nature of the active sites involved in the catalyzed reaction but changed their concentrations. (C) 2008 Elsevier B.V. All rights reserved.