Reactivity control of Ci-H bond activation over vanadium-silver bimetallic oxide cluster cations

Vanadium-silver bimetallic oxide cluster ions (V _xAg _yO _z ⁺; x=1-4, y=1-4, z=3-11) are produced by laser ablation and reacted with ethane in a fast-flow reactor. A reflectron time of flight (Re-TOF) mass spectrometer is used to detect the cluster distribution before and after the reactions. Hydrogen atom abstraction (HAA) reactions are identified over VAgO ₃ ⁺, V ₂Ag ₂O ₆ ⁺, V ₂Ag ₄O ₇ ⁺, V ₃AgO ₈ ⁺, V ₃Ag ₃O ₉ ⁺, and V ₄Ag ₂O ₁₁ ⁺ ions, in which the oxygen-centered radicals terminally bonded on V atoms are active sites for the facile HAA reactions. DFT calculations are performed to study the structures, bonding, and reactivity. The reaction mechanisms of V ₂Ag ₂O ₆ ⁺+C ₂H ₆ are also given. The doped Ag atoms with a valence state of +1 are highly dispersed at the periphery of the V _xAg _yO _z ⁺ cluster ions. The reactivity can be well-tuned gradually by controlling the number of Ag atoms. The steric protection due to the peripherally bonded Ag atoms greatly enhances the selectivity of the V-Ag bimetallic oxide clusters with respect to the corresponding pure vanadium oxide systems. Different clusters: Hydrogen atom abstraction (HAA) reactions are identified over VAgO ₃ ⁺, V ₂Ag ₂O ₆ ⁺, V ₂Ag ₄O ₇ ⁺, V ₃AgO ₈ ⁺, V ₃Ag ₃O ₉ ⁺, and V ₄Ag ₂O ₁₁ ⁺ cluster ions, in which the terminal oxygen-centered radicals O _t ^-. are active sites bonded on V atoms for the HAA reactivity (see figure). The reactivity can be tuned by controlling the number of Ag atoms, and the selectivity is enhanced by steric protection of the terminal oxygen atoms by the bridge-bonded Ag atoms.