MARIO PAGLIARO
Istituto per lo Studio dei Materiali Nanostrutturati, CNR, Palermo, Italy

First clearly identified and termed accordingly by Zhang, Li, Liu and co-workers in 2011, when the team reported that single Pt atoms supported on FeO_x - and not Pt nanoparticles (NPs) - are responsible for the high activity (3 times more active than the NP counterpart) and remarkable stability observed in CO oxidation (1), single-atom catalysis (SAC) is a shift in catalysis science due to shortly impact the chemical and energy industries (2). 

Thanks to recent fundamental work of Ananikov and co-workers in Russia (3), we know today that in industrially relevant transition metal catalysis such as in cross-coupling reactions mediated by palladium, mononuclear, cluster and nanoparticle metal species are all involved in catalysis. Commercially available samples of Pd₂(dba)₃ contain up to 40% of Pd NPs which, during catalysis, progressively decompose to form Pd complexes and clusters in solution, giving place to a “cocktail” of multiple catalytic species in solution (Figure 1). 

Single-atom catalysis is the ultimate consequence ...