Effects of thermal treatments on a NiMoO₄ precursor prepared by immobilizing Ni ²⁺_aq and MoO ²_4aq - in an organic matrix

Abstract

A novel preparation methodology of NiMoO₄ catalysts is described, consisting 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 very low temperature, with the collapse of the gel structure.

The elimination of the water representing the greatest part of the gel weight is the predominant phenomenon taking place during the thermal activation treatment and the phase composition of the oxide formed changes as follows: fast heating favours the stabilization at room temperature of the metastable tetrahedral β-NiMoO₄ phase, while slow heating allows an increased formation of the more stable octahedral α-phase.