Ex situ characterization of N2H4-, NaBH4- and NH3BH3-reduced cobalt catalysts used in NaBH4 hydrolysis

Sodium borohydride NaBH4-reduced cobalt is a very attractive material in catalyzing NaBH4 hydrolysis, as it is highly reactive and cost-effective. However, the nature of its catalytically active phase is still unknown although it has been mostly suggested as being either cobalt boride such as Co2B or an alloy Co–B. With the objective to contribute to highlight the real nature of the catalytically active phase, we performed a systematic study focusing on synthesizing different Co catalysts, characterizing them by ICP-AES, N2 adsorption/desorption, EDS, FTIR, DSC, SEM, TEM and XRD, and testing them in NaBH4 hydrolysis. Herein, it is showed that, to be highly reactive, the Co catalyst has to be reduced by a boron-containing reducing agent such as NaBH4 and ammonia borane NH3BH3. Furthermore, it has to be amorphous. None of both features were observed in the case of the hydrazine N2H4-reduced cobalt. Hence, it is suggested that the presence of boron is necessary to achieve better reactivity through electronic and geometric effects.