Hydrogen reduction kinetics of different cobalt compounds

Hydrogen reduction kinetics of cobalt oxides, carbonates, and hydroxides were investigated under both isothermal (300, 400, and 500 °C) and non-isothermal (30 °C to 700 °C) conditions, using thermogravimetric analysis (TGA). Isothermal data was fitted to various solid-state kinetic models, revealing that the most suitable model in all temperatures for the reduction of studied compounds was R2 and AE1 in the case of Co 2 CO 3 (OH) 2 at 300 °C. The calculated activation energies ranged between 39.8 and 48.4 kJ/mol for the two Co 3 O 4 , 11.5–26.3 kJ/mol for CoCO 3 , 46.8–91.7 kJ/mol for Co 2 CO 3 (OH) 2 , 6.9–10.7 for Co(OH) 2 with a uniform PSD, and 24.5–28.9 kJ/mol for Co(OH) 2 with a non-uniform PSD. Isoconversional methods (Vyazovkin, Friedman, Kissinger-Akahira-Sunose, Flynn-Wall-Osawa) were applied to the non-isothermal data of four different heating rates (5, 10, 15, and 20 °C/min). The derived activation energies, as a function of conversion extent, indicated that the thermal decomposition of cobalt carbonates and hydroxides generally required higher activation energies than the subsequent reduction of CoO (approximately 40–60 kJ/mol). Decomposition of carbonates and hydroxides was found to precede the reduction of resulting CoO under a dynamic heating regime. The study showed that reduction kinetics are highly influenced by characteristics of the cobalt compounds, as well as the used process parameters. • H 2 reduction kinetics of cobalt oxides, carbonates, and hydroxides was studied. • Isothermal and non-isothermal data was collected with TGA. • Model-based and model-free methods were used to calculate the kinetic triplet. • Kinetics are highly dependent on precursor characteristics and process parameters.