Composition dependent selectivity in the coadsorption of H2O and CO on pure and binary silver-gold clusters

► Composition dependent reactivity of mass-selected AgnAum+ clusters has been investigated. ► Binding energies of H2O to AgnAum+ (n + m = 3) have been determined experimentally and theoretically. ► Coadsorption of CO and H2O to AgnAum+ has been observed only for Ag2Au+. ► First step for a catalytic water gas shift chemistry on AgnAum+ has been established.