CH Activation on Aluminum–Vanadium Bimetallic Oxide Cluster Anions

Abstract

Aluminum-vanadium bimetallic oxide cluster anions (BMOCAs) have been prepared by laser ablation and reacted with ethane and n-butane in a fast-flow reactor. A time-of-flight mass spectrometer was used to detect the cluster distribution before and after the reactions. The observation of hydrogen-containing products AlVO(5)H(-) and Al(x)V(4-x)O(11-x)H(-) (x=1-3) strongly suggests that AlVO(5)(-) and Al(x)V(4-x)O(11-x)(-) (x=1-3) can react with ethane and n-butane by means of an oxidative dehydrogenation process at room temperature. Density functional theory studies have been carried out to investigate the structural, bonding, electronic, and reactive properties of these BMOCAs. Terminal-oxygen-centered radicals (O(t)(.)) were found in all of the reactive clusters, and the O(t)(.) atoms, which prefer to be bonded with Al rather than V atoms, are the active sites of these clusters. All the hydrogen-abstraction reactions are favorable both thermodynamically and kinetically. To the best of our knowledge, this is the first example of hydrogen-atom abstraction by BMOCAs and may shed light on understanding the mechanisms of C−−H activation on the surface of alumina-supported vanadia catalysts.

Catalytic Redox Reactions in the CO/N2O System Mediated by the Bimetallic Oxide‐Cluster Couple AlVO3+/AlVO4+

“…[19] The DFT calculations have been carried out using the Gaussian 09 program [20] employing the hybrid B3LYP exchange-correlation functional [21] with the unrestricted Kohn-Sham solution, [22] and TZVP basis sets. [23] The unrestricted B3LYP/TZVP level of theory proved reliable in previous studies of cationic, [24] anionic, [25] and neutral [10] AlVO 5 À , [27] V 2 SiO 8 À , [28] V 2 SiO 7 + , [11d] and V 3 PO 10 +[11a,c] and their gas-phase reactions with small alkanes. For the optimization of transition structures (TS), we employed either the Berny algorithm [29] or the synchronous transitguided quasi-Newton (STQN) method.…”

Doping Effects in Cluster‐Mediated Bond Activation

“…[95] This conjecture was questioned by gas-phase experiments with metal-free oxide clusters;for example,[P 4 O 10 ]C + activates methane under ambient conditions with an efficiencyof66% relative to the collision rate. [97] With regard to heteronuclear clusters, for example,[ V 4Àn P n O 10 ]C + , [80] [(V 2 O 5 ) n (SiO 2 ) m ] +/À (n = 1, 2; m = 1-4), [98] or [V n Al m O o ] +/À (n + m = 2, 3, 4; o = 3-10), [99] they all possess ah igh spin density located at at erminal oxygen atom that is not bound to the transition metal vanadium but to the main-group atom, that is AlÀO t C,S i À O t C,o rP ÀO t C.T he V=O t unit is completely inert. [97] With regard to heteronuclear clusters, for example,[ V 4Àn P n O 10 ]C + , [80] [(V 2 O 5 ) n (SiO 2 ) m ] +/À (n = 1, 2; m = 1-4), [98] or [V n Al m O o ] +/À (n + m = 2, 3, 4; o = 3-10), [99] they all possess ah igh spin density located at at erminal oxygen atom that is not bound to the transition metal vanadium but to the main-group atom, that is AlÀO t C,S i À O t C,o rP ÀO t C.T he V=O t unit is completely inert.…”

“…[96] Similarly,o ligomeric aluminum oxide clusters [(Al 2 O 3 ) n ]C + (n = 3-5) with an even number of aluminum atoms are capable to activate CH 4 at room temperature. [97] With regard to heteronuclear clusters, for example,[ V 4Àn P n O 10 ]C + , [80] [(V 2 O 5 ) n (SiO 2 ) m ] +/À (n = 1, 2; m = 1-4), [98] or [V n Al m O o ] +/À (n + m = 2, 3, 4; o = 3-10), [99] they all possess ah igh spin density located at at erminal oxygen atom that is not bound to the transition metal vanadium but to the main-group atom, that is AlÀO t C,S i À O t C,o rP ÀO t C.T he V=O t unit is completely inert. Obviously, questions regarding the actual nature of the active site in heteronuclear oxo clusters and the particular role of the various components of ah eterogeneous catalyst are once more raised.…”

Methane Activation by Yttrium‐Doped Vanadium Oxide Cluster Cations: Local Charge Effects

“…[3][4][5][6][7][8] The O À C-containing oxide anions usually have lower reactivity than the corresponding cations and can abstract a hydrogen atom only from more reactive alkanes such as ethane or butane. [9][10] The charged states (cationic versus anionic) can thus significantly influence cluster reactivity. [9,11] Herein, the experimental and computational studies demonstrate that for a certain charge state, that is the cationic state, the local charge distribution around the O À C centers can also change the cluster reactivity toward methane dramatically.…”