Size-Dependent Reactivity of Nano-Sized Neutral Manganese Oxide Clusters toward Ethylene

Neutral manganese oxide clusters with the general composition Mn_{2 N}O_{3 N+x} (N=2–22; x=−1, 0, 1) with dimensions up to a nanosize were prepared by laser ablation and reacted with C₂H₄ in a fast flow reactor. The size-dependent reactivity of C₂H₄ adsorption on these clusters was experimentally identified and the adsorption reactivity decreases generally with an increase of the cluster size. Density functional theory calculations were performed to study the geometrical and electronic structures of the Mn_{2 N}O_{3 N} (N=1–6) clusters. The calculated results indicated that the coordination number and the charge distribution of the metal centers are responsible for the experimentally observed size-dependent reactivity. The highly charged Mn atoms with low coordination are preferential to adsorb C₂H₄. In contrast, the neutral manganese oxide clusters are completely inert toward the saturated hydrocarbon molecule C₂H₆. This work provides new perspectives to design related materials in the separation of hydrocarbon molecules.