Nanosheet array-like NixMg3-xAl-LDH/rGO hybrids loaded atomically precise Aun nanoclusters for the solvent-free oxidation of benzyl alcohol

Abstract

A series of hierarchically structured hybrids NixMg3-xAl-LDH/rGO (LDH: layered double hydroxides, x = 1, 1.5 and 2, rGO: reduced graphene oxide) supported atomically precise Aun (n = 25, 38 and 127) nanoclusters (NCs) catalysts Aun/NixMg3-xAl-280 were firstly prepared via a double pH-controlled electrostatic adsorption method using captopril-capped Aun NCs as precursors followed proper calcination. Detailed characterizations show that the as-obtained hierarchically structured Aun NCs catalysts possess the nanosheet array-like structure formed by the LDHs nanosheets (∼55–70 × 10 nm) interdigitated vertically grown on the both sides of rGO layers, and Aun NCs with size of 1.0–1.9 nm are mainly dispersed on the edge and cross-linking sites of LDH/rGO hybrid. All the hierarchically structured Aun NCs catalysts exhibit excellent catalytic activity for the solvent-free oxidation of benzyl alcohol without additional base, and the activities show a volcanic trend with increasing Ni/Mg ratios and gradually decrease with the increased Au atomicities in Aun clusters. The highest TOF value of 5118 h−1 for the Au25/Ni1.5Mg1.5Al-280 can be ascribed to the smallest Au25 NCs containing the Au0/Auδ+-Ni2+/Mg2+–OH interface with the highest Auδ+/(Au0 + Auδ+) ratio, and the strongest Au25−LDH/rGO synergistic interaction along with hierarchical nanosheet array-like structure facilitating the transmission and diffusion of the reactants. The present work provides a new idea for preparing the hierarchically structured LDH/rGO hybrid supported metal nanoclusters catalysts with high-performance for various catalytic applications.