Fe2 O+ Cation Mediated Propane Oxidation by Dioxygen in the Gas Phase.

The mass-selected Fe2 O+ cation mediated propane oxidation by O2 was investigated by mass spectrometry and density functional theory calculations. In the reaction of Fe2 O+ with C3 H8 , H2 was liberated by C-H bond activation to give Fe2 OC3 H6+ . Interestingly, when a mixture of C3 H8 /O2 was introduced into the reactor, an intense signal that corresponded to the Fe2 O2+ cation was present; the experiments indicated that O2 was activated in its reaction with Fe2 O(C3 H6 )+ to give Fe2 O2+ and C3 H6 O (acetone or propanal). A Langmuir-Hinshelwood-like mechanism was adopted in the propane oxidation reaction by O2 on gas-phase Fe2 O+ cations. In comparison with the absence of Fe2 O2+ in the reaction of Fe2 O+ with O2 , the ligand effect of C3 H6 on Fe2 OC3 H6+ is important in the oxygen activation reaction. The theoretical results are consistent with the experimental observations. The propane oxidation by O2 in the presence of Fe2 O+ might be applied as a model for alkane and O2 activations over iron oxide catalysts, and the mechanisms and kinetic data are useful for understanding corresponding heterogeneous reactions.

Direct hydroxylation of benzene to phenol mediated by nanosized vanadium oxide cluster ions at room temperature.

Gas-phase vanadium oxide cluster cations and anions are prepared by laser ablation. The small cluster ions (<1000 amu) are mass-selected using a quadrupole mass filter and reacted with benzene in a linear ion trap reactor; large clusters (>1000 amu) with no mass selection are reacted with C6H6 in a fast flow reactor. Rich product variety is encountered in these reactions, and the reaction channels for small cationic and anionic systems are different. For large clusters, the reactivity patterns of (V2O5) n+ (n = 6-25) and (V2O5) n O- (n = 6-24) cluster series are very similar to each other, indicating that the charge state has little influence on the oxidation of benzene. In sharp contrast to the dramatic changes of reactivity of small clusters, a weakly size dependent reaction behavior of large (V2O5)6-25+ and (V2O5)6-24O- clusters is observed. Therefore, the charge state and the size are not the major factors influencing the reactivity of nanosized vanadium oxide cluster ions toward C6H6, which is not common in cluster science. In the reactions with benzene, the small and large reactive vanadium oxide cations show similar reactivity of hydroxyl radicals (OH•) toward C6H6 at higher and lower temperatures, respectively; different numbers of vibrational degrees of freedom and the released energy during the formation of adduct complexes can explain this intriguing correlation. The reactions investigated herein might be used as the models of how to realize the partial oxidation of benzene to phenol in a single step, and the observed mechanisms are helpful to understand the corresponding heterogeneous reactions, such as those over vanadium oxide aerosols and vanadium oxide catalysts.

Liberation of three dihydrogens from two ethene molecules as mediated by the tantalum nitride anion cluster Ta3N2- at room temperature.

The reactivity of gas-phase cluster anions Ta3N2- with C2H4 under thermal collision conditions was studied by mass spectrometry in conjunction with density functional theory calculations. The full dehydrogenation of the C2H4 molecule was observed, with the formation of two dihydrogen molecules. Interestingly, the two carbon atoms originating from the first C2H4 molecule are used to construct another cluster Ta3N2C2-, which can activate one more C2H4 releasing one H2 molecule. Therefore, three dihydrogen molecules are liberated from two ethene molecules in the overall reaction. The full dehydrogenation of C2H4 by gas-phase anions as well as the structure and reactivity of M-N-C (M: transition metal) cluster is reported for the first time. The properties of Ta3N2- and Ta3N2C2- elucidated herein are of use in providing fundamental information that is necessary to tailor the design of new and effective catalysts by applying the related materials.

Origin of the Different Reactivity of the Triatomic Anions HMoN- and ZrNH- toward Alkane: Compositions of the Active Orbitals.

The reactivity of the triatomic anions HMoN- and ZrNH- toward alkanes was investigated by means of mass spectrometry in conjunction with density functional theory calculations. HMoN- can activate C-H bond of ethane with the liberation of ethene and hydrogen molecules, and the generation of hydrogen molecules is the major reaction channel; however, no C-H bond activation of ethane was observed over ZrNH- ion, and the density functional theory calculations suggest this pathway is hampered by intrinsic energy barrier. In sharp contrast, another triatomic anion HNbN- can bring about methane activation under thermal conditions, as reported previously. A strong dependence of the chemical reactivity of alkane activation on compositions of active orbitals in the above-mentioned systems is discussed. This combined experimental/computational study may provide new insights into the importance of compositions of active orbitals and their essential role in the reactions of related systems with alkanes.