▎ 摘　　要

Tetrametallic core-shell Ag@CoNiFe nanoparticles (NPs) supported on graphene have been synthesized by a facile one-step in situ procedure for the first time. We tuned the reducing ability of the reductants to control the structure and particle size of the as-synthesized NPs. The use of weaker reducing agents, such as ammonia borane (AB) and methylamine borane (MeAB), result in the core-shell structure, whereas the stronger reducing agent NaBH4 results in alloy NPs. The as-synthesized core-shell NPs reduced by MeAB possess a smaller particle size and exhibit a superior catalytic activity compared to the core-shell NPs reduced by AB and alloy NPs reduced by NaBH4 for the hydrolytic dehydrogenation of AB. Moreover, the turnover frequency of the as-synthesized tetrametallic core-shell NPs is 118.5 mol(H2) min(-1)mol(Ag)(-1), which is higher than that of Ag-based trimetallic, bimetallic core-shell, and alloy counterparts and even higher than that of most reported noble-metal-based NPs. Kinetic studies indicate that the catalytic hydrolysis of AB and MeAB by the Ag@CoNiFe/graphene NPs is a first-order reaction. Furthermore, the as-prepared NPs exert good catalytic activities and recycle stabilities towards the hydrolysis of AB. Additionally, the as-prepared NPs display magnetic recyclability, which makes the practical recycling of the NPs more convenient.