Preparation of CoB catalysts supported on raw and Na-exchanged bentonite clays and their application in hydrogen generation from the hydrolysis of NaBH4

Abstract

The aim of this work is to prepare CoB catalysts supported on raw bentonite (CoB/bentonite) and Na-exchanged bentonite (CoB/Na-bentonite) by the impregnation and chemical reduction method. The prepared catalysts were characterized using X-ray diffractometry (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. The activities of the catalysts were tested in the hydrolysis reaction of sodium borohydride (NaBH4) in a semi-batch system. The volume of the evolved hydrogen gas was determined by a water displacement method. The effects of catalyst amount, NaOH (a base stabilizer) concentration, NaBH4 concentration and solution temperature on the hydrogen generation rate were investigated. The maximum hydrogen generation rates were determined as 921.94 mL/min.gcat for CoB/bentonite and 1601.45 mL/min.gcat for CoB/Na-bentonite when the 5 wt % NaBH4 and 10 wt % NaOH solutions were used at 50 °C. The activation energies (Ea) of the hydrolysis reaction over CoB/bentonite and CoB/Na-bentonite were determined as 55.76 and 56.61 kJ/mol, respectively.