Intrinsic reduction kinetics of cobalt- and nickel-titanates by hydrogen

The isothermal reduction of synthetic CoTiO₃ and NiTiO₃ in hydrogen (1 atm) was investigated using thermogravimetric analysis technique in the temperature range, 928–1287 K (CoTiO₃) and 884–1387 K (NiTiO₃). Shallow beds of fine titanate powders were reduced by hydrogen at a high flow rate. Quenched samples were analyzed by scanning electron microscopy. The rates of the reaction of the titanates with H₂ were very fast during the reduction of Co²⁺, Ni²⁺, or Fe²⁺ ions into metals. The reduction of the remaining titanium oxide was very slow. The activation energy for the reduction of CoTiO₃ by hydrogen to Co and TiO₂ was evaluated to be 151 ± 1 kJ/mol, and the activation energy for the reduction of NiTiO₃ by hydrogen to Ni and TiO₂ was evaluated to be 153 ± 1 kJ/mol. The study was complemented by hydrogen reduction of synthetic TiO₂ (rutile). The results were also compared with the hydrogen reduction of FeTiO₃.