NaBH4 formation mechanism by reaction of sodium borate with Mg and H2

It has been reported that sodium (potassium) borohydride can be formed by reaction of sodium (potassium) borate with Mg and hydrogen or magnesium hydride. However, few investigations on reaction mechanism have been reported. Here, we studied the NaBH4 formation mechanism of Mg + NaBO2 + 2H2 = NaBH4 + MgO through morphology observations, structure and micro composition analyses. It was found that when heating the reactor to 400 oC, NaBO2 particles were agglomerated with Mg particles and a NaBO2 network was formed due to the sintering effect. With further heating the reactor, a porous product layer (composed of NaBH4 and MgO) was formed on Mg particles. It was found that no matter whether Mg was hydrogenated or not, Mg could react with sodium borate and hydrogen to form sodium borohydride. Elevating the reaction temperature was of benefit to NaBH4 formation. Higher NaBH4 yield can be obtained by using partially hydrogenated then dehydrogenated Mg