Water activation by small free ruthenium oxide clusters

Abstract

The reactions of ruthenium clusters, Ru_x⁺ (x = 2–5), and ruthenium oxide clusters, Ru_xO_y⁺ (x = 2–5, y = 1–2), with water molecules have been investigated by gas phase ion trap mass spectrometry and first principle density functional calculations. The joint experimental and theoretical study reveals that the reactions of the ruthenium oxide clusters with water are considerably more efficient. This is assigned theoretically to the stronger binding of the water molecules to Ru_xO_y⁺ and, more importantly, to water activation leading to an efficient hydrogen transfer reaction from the water molecules to the oxygen atoms of the ruthenium oxide clusters. The theoretically predicted hydrogen shift reaction has been confirmed experimentally through ¹⁶O/¹⁸O isotope exchange experiments. Calculated energy profiles for the reactions of selected oxide clusters with water illustrate that the oxygen isotope exchange relies on the facile transfer of hydrogen atoms via [1,3] shift reactions between the oxygen atoms of the complexes due to the relatively low barriers involved. These findings might open perspectives for the future realization of water oxidation driven by ruthenium oxide clusters.