Size-Dependent Reactivity of Co n - ( n = 5-25) Cluster Anions toward Carbon Dioxide.

A fundamental understanding of the reactivity evolution of nanosized clusters at an atomically precise level is pivotal to assemble desired materials with promising candidates. Benefiting from the tandem mass spectrometer coupled with a high-temperature ion-trap reactor, the reactions of mass-selected Co _n ^- ( n = 5-25) clusters with CO ₂ were investigated and the increased reactivity of Co _20-25 ^- was newly discovered herein. This finding marks an important step to understand property evolution of subnanometer metal clusters (Co ₂₅ ^- , ∼0.8 nm) atom-by-atom. The reasons behind the increased reactivity of Co _20-25 ^- were proposed by analyzing the reactions of smaller Co _6-8 ^- clusters that exhibit significantly different reactivity toward CO ₂ , in which a lower electron affinity of Co _n contributes to the capture of CO ₂ while the flexibility of Co _n ^- could play vital roles to stabilize reaction intermediates and suppress the barriers of O-CO rupture and CO desorption.