Metal clusters confined in porous nanostructures: Synthesis, properties and applications in energy catalysis

Metal nanoclusters (MNCs), with size between metal nanoparticle (NPs) and atom, have aroused increasing interests for their unusual electronic structures, physical and chemical properties. However, the small diameter of MNCs makes them easily agglomerate and difficult to synthesize, which largely limits their wide application. Therefore, obtaining size-precise and highly stable MNCs is one of the research hotspots in the metal cluster field. To this end, porous materials have been considered a class of promising templates to not only control the size of nanoclusters (NCs) but also prevent their aggregation and improve their catalytic stability. To date, various porous materials and synthetic techniques have been extensively applied to prepare MNCs. The stable porous structures enable them inherent superiority in confining small MNCs and thus improving the catalytic performance. This review outlines the significant advance in MNCs/porous template composites with their multiple synthesis strategies, structural characterization and energy catalytic applications. At last, we give the prospects and challenges of MNCs from the perspective of their controllable preparation as well as potential applications.