A novel dehydrogenation style of NH3BH3 by catalyst of transition metal clusters

摘要

The dehydrogenation of ammonia-borane (NH3BH3, AB) by transition metal (TM) catalyst has been under intense scrutiny in experiments but a sound molecular level understanding has remained elusive. Herein, using the density functional theory (DFT) method, AB dehydrogenation mechanistic routes underscores the importance of formations of metal-hydrogen intermediate in the presence of Cu-2, Fez, FeCu dimers and Fe-12 Cu cluster. Its formation involves the stepwise or concerted transfer of H(B) and H(N) hydrogen atoms from AB to metal atom, which is different from the previously proposed dehydrogenation mechanism that one H(N) hydrogen atom is firstly transferred to B atom and then the polymerized H-2 molecule is released from B atom. The metal-dihydride Cu2H2 rather than the dissociated H-2 is ultimately derived for the catalytic reaction between Cu-2 and AB. Nevertheless, with respect to the dehydrogenation of pristine AB, the release of one equiv of H-2 molecule per AB can be significantly promoted in a kinetically fast and thermodynamically favorable way by the catalysts of Fe-2, FeCu, and Fe-12 Cu. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.