Reaction pathways and hydrogen production via ethanolysis, methanolysis and hydrolysis reactions of sodium borohydride by using p-tert-butylcalix[4]arene complexes: molecular dynamics study

Abstract

Here we employed extended tight-binding DFT based molecular dynamics (MD) simulations to investigate the dehydrogenation reaction mechanisms of sodium borohydride (NaBH4) supported X metal-doped p-tert-butylcalix[4]arene (X = Ni, Co, Ru and Pd) complexes (Calixarene(4)-Cplx) in water, methanol (MeOH) and ethanol (EtOH) environments. Also, for the performance of nano-catalyst systems through NaBH4 hydrolysis, methanolysis and ethanolysis was investigated. A key finding is that the interaction of the metal atom and hydroxyl molecular groups in the catalyst with the hydroxyl groups in MeOH and EtOH molecules creates metastable hydrogen bonds in the system. In this case, the dehydrogenation reaction appears to accelerate. However, for stability, this hydrogen bonding must be eliminated. This requires additional barrier energy for the catalyst to stabilize. This state makes the rate of H2 formation slows down. When Co, Ni Pd and Ru- Calixarene(4)-Cplx are dropped into water instead of ethanol, the increase in H2 amount occur as 35%, 78.57%, 113.2% and 53.33%. It has been determined that when X metal interpenetrate into Calixarene(4)-Cplx are used, hydrolysis and methanolysis of NaBH4 exhibit higher H2 evaluation than NaBH4 ethanolysis. Moreover, the better H2 production rate (2.6 times more) is observed in supported catalysts compared to non-supported catalyst.