“…Our results agree with the theoretical and experimental studies by Feng et al [68] that the (110)s urfaceo fPm3 m PdIn with single-atom Pd sites shows high selectivity for C 2 H 2 hydro-genationt oC 2 H 4 ,w hereas the (111)s urfaceo fP4/mmm Pd 3 In with Pd trimer sites shows low selectivity.T hus, the catalytic activity and selectivity of C 2 H 4 formationo ver aP d-doped Cu(111)s urfacem arkedlyd ependo nt he Pd geometrical distribution, namely,the surface Pd ensemblee ffect. [7,9] Overall, for the surfacee nsemble, these surface ensemble models can also presentt he surfaceP dsegregation over the Cu(111)s urface, aP d-doped Cu(111)s urface with the reduction of contiguousP ds ites as active sites is highly efficient in C 2 H 2 hydrogenation to C 2 H 4 ,which can suppress ethane formation as ar esult of the surface Pd ensemble. Particularly,t he Pd 1 Cu 8 surfacew ith the single-atom Pd sites andt he smallest surfaceP de nsemble significantly enhances the selectivity towards C 2 H 4 formation.…”