Sintering of subnano cluster catalysts is a serious limitation for their practical use. While subnano cluster catalysts exhibit unique size-dependent activity and selectivity, along with superior atom efficiency, along with their ability to break past scaling relations, their lack of stability with respect to sintering means that typically they rapidly deactivate compared to larger nanoparticles (NPs). As a result, they are unlikely to persist long enough under realistic reaction conditions to make use of their unique properties. The sintering of oxide-supported subnanoclusters is generally accepted to proceed via Ostwald ripening, where atoms detach from clusters, diffuse on the surface, and join other clusters. Because larger clusters tend to be more stable than small clusters due to higher metal-metal coordination, ripening leads to growth of larger clusters at the expense of small clusters. This is in contrast to the Smoluchowski ripening, which occurs by surface migration and coalescence of entire clusters. The thermodynamic driving force in both cases is the size dependence of surface energy, which decreases with increasing size. Furthermore, it has been shown experimentally that for small NPs consisting of 68+ atoms, sintering is slower for a more monodisperse NP size distribution, compared to NPs with a broader size distribution. because monodispersity minimizes difference in surface energy of the different NPs.