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.

► Evaluation of the kinetic parameters of CoWO4 during its reduction with methane. ► CoWO4 (CW) promoted with 10% Ni (CW–Ni) and 10% La2O3 (CW–La) as oxygen carriers. ► Reduction activation energies: CW, CW–Ni and CW–La were 53, 32 and 33 kcal/mol. ► Ni catalytic influence and La2O3 promoting action over the reaction rate of CW. ► Activation energies indicate that the process is controlled by chemical reaction.