Structural properties and reactivity of bimetallic silver-gold clusters

Bimetallic silver-gold clusters are well suited to studychanges in metallic versusionic properties involving charge transfer as a function ofthe size and the composition. We present structures, ionizationpotentials (IP) and vertical detachment energies (VDE) forneutral and charged bimetallicAu_nAg_m (2(n +m)5) clusters obtained fromdensity functional level of theory. In the stable structures ofthese clusters Au atoms assume positions which favor chargetransfer from Ag atoms. In clusters with equal numbers of heteroatoms (n =m = 1- 4) heteronuclearbonding is preferred to homonuclear bonding, giving rise tolarge values of ionization potentials. For larger clusters(n=m=5, 10) stable structures do not favorneither hetero bonding nor segregation into the singlecomponents, although they exhibit more metallic than ionicfeatures. This remains valid also forAu₈Ag₁₂ clustercharacterized by strong charge transfer to gold subunit. Theinfluence of doping of pure gold clusters with silver atoms onVDE and IP values is discussed in context of their reactivitytowards O₂ and CO molecules. As astarting point we consider reactivity towards CO andO₂ molecules on the example ofAgAu^- dimer. The results show thatthe catalytic cycle can be fullfilled.