The source of the catalytic activity in homogeneous catalysts and metalloenzymes is often coordinatively unsaturated(CUS)transition metal(TM)cations,which can undergo facile electron transfer and promote catalytic reactions.Organic ligands and proteins confine these CUS cations,making them highly reactive and stable.In heterogeneous catalysis,however,confining these highly active CUS centers on an inorganic solid so that they are robust enough to endure the reaction environment while staying flexible enough to perform their catalysis remains a challenge.We describe a strategy to stabilize the active CUS centers on the solid surface at the interface between a TM oxide(TMO)and a noble metal(NM).NMs have high electron negativity and low oxygen affinity.TM cations of the oxide bind strongly to NM atoms at the interface,forming oxygen-terminated-bilayer TMO nanostructures.The resulting CUS sites at the edges of the TMO nanostructure are highly active for catalytic oxidation reactions.Meanwhile,the strong interactions between TMOs and NMs prevent further oxidation of the bilayer TMO phases,which would otherwise result in the saturation of oxygen coordination and the deactivation of the CUS cations.Here,I discuss our recent progress on oxide-on-metal inverse catalysts,mainly the TMO-on-Pt(TM = Fe,Co,and Ni)and TMO-on-Au systems,and the interface-confinement effect based on studies in both model catalyst systems and real supported nanocatalysts.We showed that the interface confinement effect can be employed to design highly efficient novel catalysts and that the inverse oxide-on-metal catalysts may find wide applications in heterogeneous catalysis.