The reaction of Co 2 (CO) 8 with partially hydroxylated ZnO has been studied. Formation of Co 4 (CO) 1 2 deposited on the surface, and disproportionation of Co 2 (CO) 8 to Co 2 + and [Co(CO) 4 ] - has been evidenced. [Co(CO) 4 ] - has been characterized on the surface by in situ FTIR spectroscopy. Co 2 + and [Co(CO) 4 ] - were extracted from the surface with [PPN]Cl. Chemisorption of [PPN] [Co(CO) 4 ] on the surface, in presence or not of Co 2 + ions, suggests that, when Co 2 (CO) 8 reacts with ZnO, Co 2 + / [CO(CO) 4 ] - homonuclear ion-pairing species on the surface are produced. This supported molecular species is related to the catalytic activity in ethylene hydroformylation with high selectivity to propanal production.