Preadsorption Effect of Carbon Monoxide on Reactivity of Cobalt Cluster Cations toward Hydrogen.

We report gas-phase reactions of free Con(CO)m+ (n = 3-11, m = 0-2) with H2, expecting a catalytic reaction of coadsorbed CO and H2 on Con+. Preadsorption of CO molecules is found to promote H2 adsorption, in particular, on Con(CO)+ (n = 5, 8-10). Density functional theory (DFT) calculations reveal that the reactivity is governed by the molecular-orbital energy of Con+, which is tuned by preadsorbed CO molecules. Collision-induced-dissociation experiments performed on ConCOH2+ (n = 8-10) imply that at least some of the CO and H2 molecules are bound together on Con+.