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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]

Searching the global minimum (GM) structures of metal clusters is of great importance in cluster science. Very recently, the global optimization method based on deep neural network combined with transfer learning (DNN-TL) was developed to improve the efficiency of optimizing the GM structures of metal clusters by greatly reducing the number of samples to train the DNN. Aiming to further enhance the sampling efficiency of the potential energy surface and the global search ability of the DNN-TL method, herein, an advanced global optimization method by embedding genetic algorithm (GA) into the DNN-TL method (DNN-TL-GA) is proposed. In the case of the global optimization of Ptn (n=9–15) clusters, the DNN-TL-GA method requires only a half number of samples at most with respect to the DNN-TL method to find the GM structures. Meanwhile, the DNN-TL-GA method saves about 70%-80% of computational costs, suggesting the significant improved efficiency of global search ability. There are much more samples distributed in the area of the potential energy surface with low energies for DNN-TL-GA (25% for Pt14) than for DNN-TL (<1% for Pt14). The success of the DNNTL-GA method for global optimization is evidenced by finding unprecedented GM structures of Pt16 and Pt17 clusters. [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]

A fundamental understanding of the exact structural characteristics and reaction mechanisms of interface active sites is vital to engineering an energetic metal–support boundary in heterogeneous catalysis. Herein, benefiting from a newly developed high-temperature ion trap reactor, the reverse water–gas shift (RWGS) (CO2 + H2 → CO + H2O) catalyzed by a series of compositionally and structurally well-defined RhnVO3,4− (n = 3–7) clusters were identified under variable temperatures (298–773 K). It is discovered that the Rh5–7VO3,4− clusters can function more effectively to drive RWGS at relatively low temperatures. The experimentally observed size-dependent catalytic behavior was rationalized by quantum-chemical calculations; the framework of RhnVO3,4− is constructed by depositing the Rhn clusters on the VO3,4 "support", and a sandwiched base–acid–base [Rhout−–Rhin+–VO3,4−; Rhout and Rhin represent the outer and inner Rh atoms, respectively] feature in Rh5–7VO3,4− governs the adsorption and activation of reactants as well as the facile desorption of the products. In contrast, isolated Rh5–7− clusters without the electronic modification of the VO3,4 "support" can only catalyze RWGS under relatively high-temperature conditions. [ABSTRACT FROM AUTHOR]

Cost-effective and readily accessible 3d transition metals (TMs) have been considered as promising candidates for alkane activation while 3d TMs especially the early TMs are usually not very reactive with light alkanes. In this study, the reactivity of Vn+ and VnO+ (n = 1–9) cluster cations towards ethane under thermal collision conditions has been investigated using mass spectrometry and density functional theory calculations. Among Vn+ (n = 1–9) clusters, only V3–5+ can react with C2H6 to generate dehydrogenation products and the reaction rate constants are below 10−13 cm3 molecule−1 s−1. In contrast, the reaction rate constants for all VnO+ (n = 1–9) with C2H6 significantly increase by about 2–4 orders of magnitude. Theoretical analysis evidences that the addition of ligand O affects the charge distribution of the metal centers, resulting in a significant increase in the cluster reactivity. The analysis of frontier orbitals indicates that the agostic interaction determines the size-dependent reactivity of VnO+ cluster cations. This study provides a novel approach for improving the reactivity of early 3d TMs. [ABSTRACT FROM AUTHOR]

Nitrogen (N2) fixation is a challenging task for chemists. Adsorption of N2 on transition metal (TM) sites has been identified as a prerequisite for activating the very stable N≡N triple bond in both industrial and biological processes. The importance of π back-donation (filled orbitals of TM → π* orbitals of N2) between metal sites and N2 has been well elucidated while the role of another classic orbital interaction, namely σ donation (σ orbitals of N2 → empty orbitals of TM), remains ambiguous. Herein, the size-dependent reactivity of trinuclear rhodium deuteride cluster anions Rh3Dn− (n = 0–3) toward N2 adsorption in the gas phase was investigated experimentally and theoretically. A reverse relationship that higher electron-donating ability of clusters corresponds to lower N2 adsorption reactivity was experimentally observed, which is uncommon in N2 activation by gas-phase species. Theoretical analysis revealed that the σ donation rather than the π back-donation plays a predominant role in the adsorption complexes Rh3DnN2− and the enhanced reactivity upon D addition is ascribed to the lowered energy levels of active orbitals in Rh3Dn− as n increases. This study provides the first experimental evidence to declare the important role of σ donation and new clues for the design of reactive metal species in nitrogen fixation. [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]