Porous nitrogen-doped carbon-immobilized bimetallic nanoparticles as highly efficient catalysts for hydrogen generation from hydrolysis of ammonia borane

Abstract

Two N-doped carbon materials, N-doped Vulcan XC-72 carbon labelled as NXC and graphite carbon nitride labelled as C₃N₄, were selected as supports to prepare a series of bimetallic AuM (M = Co, Ni) nanoparticles (NPs) using three different reduction ways towards mixed metal ions AuCl₄⁻ and M²⁺, and then the as-synthesized supported bimetallic AuM NPs were used as catalysts for hydrolytic dehydrogenation of ammonia borane (NH₃BH₃). All the catalysts exhibited high dispersion and small size of bimetallic NPs; however, they exhibited remarkably different catalytic activities featuring total turnover frequency (TOF) values from 6.4 to 42.1 mol_H2 mol_cat⁻¹ min⁻¹. Among all the catalysts, the NXC-immobilized AuCo NPs through in situ synthesis using NaBH₄ and NH₃BH₃ as reductants exhibited the highest activity with a total TOF value of 42.1 mol_H2 mol_cat⁻¹ min⁻¹, which was among the highest values for Co-based catalysts ever reported for hydrolytic dehydrogenation of NH₃BH₃. This remarkably enhanced activity may be attributed to the synergistic effect of the N-doped NXC support and AuCo NPs and the resulting highly efficient activation of N–B bond in NH₃BH₃. In addition, the AuCo catalysts showed good recyclability, demonstrating that they had high stability/durability.