Investigation into hydrolysis and alcoholysis of sodium borohydride in ethanol–water solutions in the presence of supported Co–Ce–B catalyst

Abstract

The efficacies of attapulgite clay (ATC)-, titanium dioxide (TiO2)- and silica gel (SG)-supported cobalt–cerium–boron (Co–Ce–B) substances as catalysts were investigated for the alcoholysis and hydrolysis of sodium borohydride (NaBH4) in ethanol–water solutions. Ce served as a helpful co-catalyst among the prepared Co–Ce–B catalysts, and the catalytic activity decreased in the following sequence: TiO2-supported > ATC-supported > SG-supported > unsupported. The effects of Ce/(Co+Ce) molar ratio, ethanol concentration, reaction temperature, NaBH4 concentration and NaOH concentration on the hydrogen production rate were investigated. For the ATC-supported catalyst, when the Ce/(Co+Ce) molar ratio was 10%, the catalyst exhibited the best catalytic activity. Optimal NaBH4 concentration, NaOH concentration and ethanol concentration to promote hydrogen generation rate was around 8 wt.%, 15 wt.% and 30 wt.%, respectively. It can be found that the addition of ATC greatly improved the recycle ability of the catalysts in the multi-cycle tests. The surface morphology of the catalysts before and after the recycle tests was studied from SEM images. The compositions of the catalysts were determined by XRD and EDS analyses. The occurrence of NaB(OH)4 in the alcoholysis by-product provided pertinent indications of ethanol recovery after the tests. The value of activation energy in the hydrogen generation process in the presence of ATC-supported Co–Ce–B catalyst was calculated to be 29.51 kJ/mol. An overall kinetic equation was also proposed.