EFFECTS OF THERMAL TREATMENTS ON A NIMOO4 PRECURSOR PREPARED BY IMMOBILIZING NI-AQ(2- IN AN ORGANIC MATRIX() AND MOO4AQ2)

A novel preparation methodology of NiMoO4 catalysts is described, cons isting in immobilizing a precursor aqueous solution containing Ni and Mo ions by gelation with agar. Compared with other precursors prepared by coprecipitation, the gel, on heating, begins to crystallize at a v ery low temperature, with the collapse of the gel structure. The elimi nation of the water representing the greatest part of the gel weight i s the predominant phenomenon taking place during the thermal activatio n treatment and the phase composition of the oxide formed changes as f ollows: fast heating favours the stabilization at room temperature of the metastable tetrahedral beta-NiMoO4 phase, while slow heating allow s an increased formation of the more stable octahedral alpha-phase.