Consecutive H₂ Oxidation Mediated by Au₂VO₄⁺ Clusters

Abstract

Laser-ablation generated gold–vanadium oxide cluster cations Au2VO x + (x = 3, 4) were mass-selected by a quadrupole mass filter and interacted with H2 in an ion trap reactor. The reactions were characterized by mass spectrometry and density functional theory calculations. The Au2VO4 + cluster can oxidize two H2 molecules consecutively to produce Au2VO3 + and then Au2VO2 +, the latter of which can react with one O2 molecule to regenerate Au2VO4 +. Therefore, a catalytic cycle for H2 oxidation by O2 mediated with the Au2VO2 + clusters can be proposed. The theoretical studies predict that the gold atoms in both Au2VO4 + and Au2VO3 + are the active adsorption sites and facilitate the heterolytic cleavage of H2 in collaboration with the separate O2– ions of the vanadium oxide support. The consecutively oxidative reactivity of Au2VO4 + is attributed to the activation and dissociation of the superoxide or peroxide species (O2 •– or O2 2–) into two reactive atomic oxygen species (O2–) with the promotional effect of gold atoms acting as electron donors. This study provides molecular-level insights into the elementary mechanisms of the H2 catalytic oxidation on the surface.

Role of Gold Atoms in Oxidation and Reduction of Cationic Rhodium–Gold Oxide Clusters, RhnAumOk+, Studied by Thermal Desorption Spectrometry and DFT Calculations

“…The bond length (0.133 nm), Wiberg bond index (1.18), and the total spin (0.85) of O 2 indicate that bridging O 2 has the form of superoxide, O 2 − . 34 It is known that such bridging O 2 can be released readily from the metal oxide cluster. 35 In fact, the energy required to remove O 2 from Rh 6 Au 2 O 6 + was calculated to be as low as 1.6 eV.…”

“…The natural charges of the O atoms are both −0.169, whereas those of the other O atoms range between −0.479 and −0.658. The bond length (0.133 nm), Wiberg bond index (1.18), and the total spin (0.85) of O 2 indicate that bridging O 2 has the form of superoxide, O 2 – . It is known that such bridging O 2 can be released readily from the metal oxide cluster .…”

H2 dissociation by Au1-doped closed-shell titanium oxide cluster anions

“…In the reactions of OsO 4 + [38] and V 4 O 10 + [39] with H 2 , the atomic oxygen radical anion O − is the reactive oxygen species (ROS). Recent studies on the reactions of gold-doped heteronuclear metal oxide clusters highlighted the importance of lattice oxygen O 2− in direct H−H bond dissociation [21][22][23][24][25], paralleling the behavior of H 2 dissociation in the condensed phase systems [54,55]. Furthermore, indirect participation of the superoxide radical (O 2 − ) has also been proposed [22,23,25].…”

“…Recent studies on the reactions of gold-doped heteronuclear metal oxide clusters highlighted the importance of lattice oxygen O 2− in direct H−H bond dissociation [21][22][23][24][25], paralleling the behavior of H 2 dissociation in the condensed phase systems [54,55]. Furthermore, indirect participation of the superoxide radical (O 2 − ) has also been proposed [22,23,25]. Herein, in the reaction of AuTi 3 O 8 − with H 2 , direct H−H bond cleavage by the Au + −O 2 2− ion pair with peroxide unit has been identified and this pathway is more facile than that by the Au + −O 2− ion pair.…”

“…Gas-phase clusters that can be studied under isolated and well controlled conditions are ideal models to uncover the mechanistic details in the related condensedphase systems [14][15][16][17][18][19][20]. Gold-doped heteronuclear metal oxide clusters are being actively studied to understand the molecular-level mechanism of bond activation by the gold-oxide perimeter sites [21][22][23][24][25][26][27][28][29][30][31][32]. In the reactions of AuCeO − ion pair is usually much less reactive than the Au + −O 2− ion pair for H 2 dissociation.…”