Several NiO samples were prepared from different nickel precursors: nickel nitrate hexahydrate, nickel acetate tetrahydrate and nickel hydroxide. All samples were characterized using BET, X-ray diffaction (XRD), temperature-programmed reduction (TPR) and scanning electron microscopy (SEM) techniques. The results showed that a careful decomposition of nickel nitrate hexahydrate until formation of Ni-3(NO3)(2)(OH)(4) and subsequently calcination of this intermediate to form NiO led to very homogeneous octahedral NiO particles. Particle size can be controlled by means of the calcination temperature (around 200 nm for 400 degreesC during 4 h and 100 run for 350 degreesC during 20 min). NiO obtained from nickel hydroxide is more amorphous with high specific surface area (161 m(2)/g) and sponge-like aspect. When nickel acetate tetrahydrate is calcined, metallic nickel is obtained together with the expected NiO phase. These samples showed different morphologies than the other prepared NiO. (C) 2003 Elsevier Science B.V. All rights reserved.