Alumina-supported nickel catalysts are widely used in industry. The synthesis of these catalysts often proceeds through coprecipitation: following the precipitation of nickel salts and drying, the material is calcined, reduced, and passivated. Each of these steps may influence the catalyst ultimately obtained. In the present study, the synthesis conditions were systematically investigated. Following precipitation, a hydrotalcite is formed. Starting from hydrotalcite precursors with varying Ni/Al ratios, the conversion to the ultimate Ni-on-alumina catalyst was studied, using TEM, TPR, XRD, and chemisorption. In particular, we examined the effect of water vapour and acidic gases-liberated during calcination-on the morphology of the catalyst ultimately obtained. Two competing mechanisms for the formation of the ultimate catalyst morphology are suggested. (C) 2001 Academic Press.