Ultra-stable metal nano-catalyst synthesis strategy: a perspective

Supported metal nanoparticles (NPs) as an important heterogeneous catalyst have been widely applied in various industrial processes. During the catalytic reaction, size of the particles plays an important role in determining their catalytic performance. Generally, the small particles exhibit superior catalytic activity in comparison with the larger particles because of an increase in low-coordinated metal atoms on the particle surface that work as active sites, such as edges and corner atoms. However, these small NPs are typically unstable and tend to migrate and coalescence to reduce their surface free energy during the real catalytic processes, particularly in high-temperature reactions. Therefore, a means to fabricate stable small metal NP catalysts with excellent sinter-resistant performance is necessary for maintaining their high catalytic activity. In this study, we have summarized recent advances in stabilizing metal NPs from two aspects including thermodynamic and kinetic strategies. The former mainly involve preparing uniform NPs (with an identical size and homogeneous distribution) in order to restrain Ostwald ripening to achieve stability, while the latter primarily involves fixing metal NPs in some special confinement materials (e.g., zeolites, mesoporous silica and mesoporous carbons), encapsulating NPs using an oxide-coating film (e.g., forming core–shell structures), or constructing strong metal–support interactions to improve stability. At the end of this review, we highlight our recent work on the preparation of high-stability metal catalysts via a unique interfacial plasma electrolytic oxidation technology, that is, metal NPs are well embedded in a porous MgO layer that has both high thermal stability and excellent catalytic activity.