Langmuir-Hinshelwood kinetic model to capture the cobalt nanoparticles-catalyzed hydrolysis of sodium borohydride over a wide temperature range

The present study focused on kinetics of hydrogen release through hydrolysis of sodium borohydride NaBH4 in the presence of cobalt nanoparticles. Our experimental conditions were quite severe as we worked over the widest temperature range ever reported (i.e. 10-90 degrees C) and at high content of hydride (mol ratio NaBH4/water of 9; i.e. 18.9 wt% NaBH4 or 6.18 mol L-1). From the hydrogen evolution curves, the reaction constant versus the NaBH4 concentration, apparent activation energy, rate constant, adsorption constant and adsorption enthalpy were determined. It was noticed that the hydrolysis kinetics depends on (i) temperature of reaction and (ii) NaBH4 concentration. Hence, the kinetic constants were analyzed using existing kinetic models. The bimolecular Langmuir-Hinshelwood model satisfactorily captured the behavior of our catalyst consisting of cobalt nanoparticles (in our experimental conditions). Herein, the kinetic data, the kinetic model, the hydrolysis mechanism and the issues still to be addressed are reported and discussed. (C) 2011 Elsevier B.V. All rights reserved.