Reactivity Trends in the Oxidation of CO by Anionic Transition Metal Oxide Clusters

Evidence obtained by experiments in the gas phase and density functional theory calculations indicates that differences in the CO binding energy to the transition metal site and the overall change in energy and spin multiplicity from reactants to products, underlie the variation in relative reactivity observed for the oxidation of CO by anionic transition metal oxide clusters. Experimental reactivity studies of MO 2 − and M 2 O 3 − (M = Fe, Co, Ni, and Cu) reveal that anionic oxide clusters with the same number of atoms and stoichiometry but different elemental composition exhibit specific trends in relative oxidation reactivity with CO. The anionic MO 2 − and M 2 O 3 − clusters are found to be most reactive for M = Fe and Cu and relatively less reactive for M = Co and Ni. Theoretical electronic structure studies within the density functional theory framework indicate that the most reactive clusters either have relatively large initial binding energies of CO to the cluster which provide sufficient energy to overcome any subsequent barriers to oxidation, or that the reaction preserves the same overall spin multiplicity from reactants to products.