Global kinetic evaluation during the reduction of CoWO4 with methane for the production of hydrogen

CoWO₄ (CW) promoted with 10% Ni (CW–Ni) and 10% La₂O₃ (CW–La) were used as oxygen carriers in redox cycles of CH₄/Ar and H₂O/Ar to evaluate their global kinetics (reaction rate, order, constant and activation energy) with methane for the production of hydrogen. CoWO₄ was synthesized by co-precipitation from equimolar solutions of Na₂WO₄ and Co(NO₃)₂ and calcined at 950 °C. Ni and La nitrate solutions were incorporated to CoWO₄ by impregnation. Kinetic data was collected by thermogravimetric analysis (TGA) at 2, 5 and 8% CH₄/Ar and at 850, 900 and 950 °C for two consecutive redox cycles. Oxidation was performed using 5% H₂O/Ar at 900 °C. Results indicate a global first order reaction for the three materials. Activation energies during the first cycle for CW, CW–Ni and CW–La were 52.8, 32 and 33.4 kcal/mol, respectively, thus reflecting the influence of Ni and La₂O₃ in a greater reaction rate with respect to CW.