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Understanding the properties of small particles working under high-temperature conditions at the atomistic scale is imperative for exact control of related processes, but it is quite challenging to achieve experimentally. Herein, benefitting from state-of-the-art mass spectrometry and by using our newly designed high-temperature reactor, the activity of atomically precise particles of negatively charged vanadium oxide clusters toward hydrogen atom abstraction (HAA) from methane, the most stable alkane molecule, has been measured at elevated temperatures up to 873 K. We discovered the positive correlation between the reaction rate and cluster size that larger clusters possessing greater vibrational degrees of freedom can carry more vibrational energies to enhance the HAA reactivity at high temperature, in contrast with the electronic and geometric issues that control the activity at room temperature. This finding opens up a new dimension, vibrational degrees of freedom, for the simulation or design of particle reactions under high-temperature conditions. [ABSTRACT FROM AUTHOR]

The reactivity of vanadium oxide cluster anions (V2O5)NO− (N = 1–18) that feature with vanadium oxyl radicals (V–O⋅−) toward the most stable alkane, methane, at 273 K has been characterized by employing a newly home-made ship-lock type reactor coupled with a time-of-flight mass spectrometer. The rate constants were determined in the orders of magnitude of 10−16–10−18 cm3 molecule−1 s−1, which significantly breaks the detection limit of predecessors that the reactivity of metal-oxyl radicals (Mn+–O⋅−) with rate constants higher than 10−14 cm3 molecule−1 s−1 could usually be measured. The dynamic structural rearrangement of the cluster skeleton has been proposed to account for the size-dependent reactivity of (V2O5)1–5O− clusters, which may also function in tuning the reactivity of large-sized (V2O5)6–18O− clusters. This work provides new insights into the mechanism of Mn+–O⋅−-mediated C–H activation of methane at a strictly molecular level and expands the activity landscape of Mn+–O⋅− radicals. [ABSTRACT FROM AUTHOR]

A high-temperature linear ion trap that can stably run up to 873 K was newly designed and installed into a homemade reflectron time-of-flight mass spectrometer coupled with a laser ablation cluster source and a quadrupole mass filter. The instrument was used to study the pyrolysis behavior of mass-selected (V2O5)NO− (N = 1–6) cluster anions and the dissociation channels were clarified with atomistic precision. Similar to the dissociation behavior of the heated metal oxide cluster cations reported in literature, the desorption of either atomic oxygen atom or molecular O2 prevailed for the (V2O5)NO− clusters with N = 2–5 at 873 K. However, novel dissociation channels involving fragmentation of (V2O5)NO− to small-sized VxOy− anions concurrent with the release of neutral vanadium oxide species were identified for the clusters with N = 3–6. Significant variations in branching ratios for different dissociation channels were observed as a function of cluster size. Kinetic studies indicated that the dissociation rates of (V2O5)NO− monotonically increased with the increase in cluster size. The internal energies carried by the (V2O5)NO− clusters at 873 K as well as the energetics data for dissociation channels have been theoretically calculated to rationalize the experimental observations. The decomposition behavior of vanadium oxide clusters from this study can provide new insights into the pyrolysis mechanism of metal oxide nanoparticles that are widely used in high temperature catalysis. [ABSTRACT FROM AUTHOR]

Due to the extraordinary catalytic activity in redox reactions, the noble metal, rhodium, has substantial industrial and laboratory applications in the production of value-added chemicals, synthesis of biomedicine, removal of automotive exhaust gas, and so on. The main drawback of rhodium catalysts is its high-cost, so it is of great importance to maximize the atomic efficiency of the precious metal by recognizing the structure–activity relationship of catalytically active sites and clarifying the root cause of the exceptional performance. This Perspective concerns the significant progress on the fundamental understanding of rhodium chemistry at a strictly molecular level by the joint experimental and computational study of the reactivity of isolated Rh-based gas phase clusters that can serve as ideal models for the active sites of condensed-phase catalysts. The substrates cover the important organic and inorganic molecules including CH4, CO, NO, N2, and H2. The electronic origin for the reactivity evolution of bare Rhxq clusters as a function of size is revealed. The doping effect and support effect as well as the synergistic effect among heteroatoms on the reactivity and product selectivity of Rh-containing species are discussed. The ingenious employment of diverse experimental techniques to assist the Rh1- and Rh2-doped clusters in catalyzing the challenging endothermic reactions is also emphasized. It turns out that the chemical behavior of Rh identified from the gas phase cluster study parallels the performance of condensed-phase rhodium catalysts. The mechanistic aspects derived from Rh-based cluster systems may provide new clues for the design of better performing rhodium catalysts including the single Rh atom catalysts. [ABSTRACT FROM AUTHOR]

Structures of stoichiometric (La2O3)n (n = 1-6) clusters have been systematically studied by theoretical calculations. Global minimum structures for these clusters are determined by genetic algorithm based global optimizations at density functional level. The ground state structure for La6O9 was found to be highly symmetric with point group Oh and the centered oxygen atom has the coordination number as large as six, which is the same as the highest coordination number of oxygen atoms in bulk La2O3. Analysis of the binding energies shows that La6O9 has a high stability among the studied clusters. The energies of the highest occupied/lowest unoccupied molecular orbitals, vertical ionization energy, and vertical electron affinity of each cluster are provided. Electronic structure of La6O9 is discussed by analysis of the frontier molecular orbitals and unpaired spin density distributions of charged clusters. [ABSTRACT FROM AUTHOR]

The reactivity of vanadium oxide cluster anions (V 2 O 5 ) N O - (N = 1-18) that feature with vanadium oxyl radicals (V-O ⋅- ) toward the most stable alkane, methane, at 273 K has been characterized by employing a newly home-made ship-lock type reactor coupled with a time-of-flight mass spectrometer. The rate constants were determined in the orders of magnitude of 10 -16 -10 -18  cm 3  molecule -1  s -1 , which significantly breaks the detection limit of predecessors that the reactivity of metal-oxyl radicals (M n+ -O ⋅- ) with rate constants higher than 10 -14  cm 3  molecule -1  s -1 could usually be measured. The dynamic structural rearrangement of the cluster skeleton has been proposed to account for the size-dependent reactivity of (V 2 O 5 ) 1 - 5 O - clusters, which may also function in tuning the reactivity of large-sized (V 2 O 5 ) 6 - 18 O - clusters. This work provides new insights into the mechanism of M n+ -O ⋅- -mediated C-H activation of methane at a strictly molecular level and expands the activity landscape of M n+ -O ⋅- radicals.

A high-temperature linear ion trap that can stably run up to 873 K was newly designed and installed into a homemade reflectron time-of-flight mass spectrometer coupled with a laser ablation cluster source and a quadrupole mass filter. The instrument was used to study the pyrolysis behavior of mass-selected (V 2 O 5 ) N O - (N = 1-6) cluster anions and the dissociation channels were clarified with atomistic precision. Similar to the dissociation behavior of the heated metal oxide cluster cations reported in literature, the desorption of either atomic oxygen atom or molecular O 2 prevailed for the (V 2 O 5 ) N O - clusters with N = 2-5 at 873 K. However, novel dissociation channels involving fragmentation of (V 2 O 5 ) N O - to small-sized V x O y - anions concurrent with the release of neutral vanadium oxide species were identified for the clusters with N = 3-6. Significant variations in branching ratios for different dissociation channels were observed as a function of cluster size. Kinetic studies indicated that the dissociation rates of (V 2 O 5 ) N O - monotonically increased with the increase in cluster size. The internal energies carried by the (V 2 O 5 ) N O - clusters at 873 K as well as the energetics data for dissociation channels have been theoretically calculated to rationalize the experimental observations. The decomposition behavior of vanadium oxide clusters from this study can provide new insights into the pyrolysis mechanism of metal oxide nanoparticles that are widely used in high temperature catalysis.

The reactions between methane and niobium oxide cluster cations were studied and compared to those employing vanadium oxides. Hydrogen atom abstraction (HAA) reactions were identified over stoichiometric (Nb2O5)N(+) clusters for N as large as 14 with a time-of-flight mass spectrometer. The reactivity of (Nb2O5)N(+) clusters decreases as the N increases, and it is higher than that of (V 2O5)N(+) for N ≥ 4. Theoretical studies were conducted on (Nb2O5)N(+) (N = 2-6) by density functional calculations. HAA reactions on these clusters are all favorable thermodynamically and kinetically. The difference of the reactivity with respect to the cluster size and metal type (Nb vs V) was attributed to thermodynamics, kinetics, the electron capture ability, and the distribution of the unpaired spin density. Nanosized Nb oxide clusters show higher HAA reactivity than V oxides, indicating that niobia may serve as promising catalysts for practical methane conversion.