Reactivity of graphene-supported Co clusters

• CO adsorption on Co clusters at on-top, bridge/hollow and edge sites. • Dissociation of CO during annealing of the as-prepared Co clusters. • Adsorption site reorganization of CO molecules upon annealing. • Reduced CO adsorption capacity and passivation on C- and O-precovered clusters. Graphene-supported Co clusters were investigated by high-resolution XPS, TPD and IRRAS using CO as a probe molecule. CO adsorption was observed at edge, on-top and bridge/hollow sites on the as-prepared clusters. Temperature-programmed XPS showed CO dissociation at T > 300 K. The CO desorption temperatures were determined by TPD measurements to be 260, 320 and 400 K for CO bridge/hollow , CO edge and CO top , respectively. The CO dissociation products were used to investigate the adsorption of CO on carbon and oxygen precovered Co clusters. Site blocking by these adatoms was found resulting in the absence of CO edge (XPS and TPD) and a decrease of the CO adsorption capacity (XPS, TPD and IRRAS). Additionally, no CO dissociation was found on the precovered clusters concluding a blocking of the catalytically active sites which are the edge sites of the clusters.