Abnormal thermal stability of sub-10 nm Au nanoparticles and their high catalytic activity

Abstract

Supported Au nanoparticles have been attracting increasing attention due to their unique catalytic performance. However, their thermal and catalytic stability against sintering and aggregation during preparation and reactions remains a serious issue in practical applications, and what is even more difficult is to solve this mutually exclusive problem by a feasible technique. Here, we propose a simple one-step ultra-low temperature interfacial plasma electrolytic oxidation (ULTPEO) process to successfully prepare sub-10 nm and highly stable Au NPs, supported on a porous MgO layer, with high activity and a long lifespan. The obtained Au NPs, with partially exposed free surfaces, are encapsulated into a porous MgO support film. This unique embedded structure restrains their sintering on the support surface during high temperature treatment even up to 600 °C and shows good thermal stability and excellent recyclability in a model reaction of the hydrogenation of 4-nitrophenol. Moreover, the developed technique allows the facile control of the average size of Au NPs down to ∼3 nm with high monodispersity by liquid nitrogen cooling, and hence a further significant improvement in catalytic activity and the lowest catalytic activation energy of ∼14 kJ mol⁻¹ among the reported literature are obtained. This simple technique is also extended to other metal NP catalysts (e.g. Ru and Pd) that support MgO and exhibit excellent catalytic activity for the hydrolysis of sodium borohydride and oxidation of silanes, respectively.