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The Sc(3)O(6)(-) cluster anions were produced by laser ablation and studied by reaction with n-butane in a fast flow reactor and by photoelectron spectroscopy. The reactivity experiments indicated that one Sc(3)O(6)(-) cluster can activate two n-butane molecules consecutively with rate constants on the order of 10(-10) cm(3) molecule(-1) s(-1) under near room-temperature conditions, suggesting that the even-electron system Sc(3)O(6)(-) has a highly reactive electronic structure. The photoelectron spectroscopy determined a high vertical detachment energy (VDE) of 5.63 ± 0.08 eV for the Sc(3)O(6)(-) cluster. Density functional computations indicated that the lowest energy isomer of Sc(3)O(6)(-) is an oxygen-centered biradical with a high VDE and is highly reactive toward n-butane, which is in good agreement with the experiments. The Sc(3)O(6)(-) cluster may serve as an ideal model system to provide insight into the real-life chemistry involved with the coupled O(-)˙···O(-)˙ dimers over the surfaces of metal oxide catalysts.

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]

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]

The reactivity of chromium oxide cluster anions (CrO3)1−4O− towards low carbon (C1−C4) alkanes has been experimentally investigated at 298 K by employing a homemade ship-lock-type reactor coupled with a time-of-flight mass spectrometer. The results demonstrate that while CrO4− and Cr2O7− clusters could abstract a hydrogen atom from C2H6 and CH4, respectively, Cr3O10− and Cr4O13− clusters were found to be inert towards n-C4H10 within the detection limit. Theoretical results reveal that CrO4− and Cr2O7− clusters possess delocalized chromium-bonded oxygen radicals (Cr−O−·), which rationalizes the hydrogen atom abstraction reactions between (CrO3)1,2O− clusters and alkanes. However, the active sites of (CrO3)3,4O− clusters evolve to peroxide species (O22−), which exhibit inferior activity compared to O−· radicals. The increase of Cr-3d orbital energy driven by the more negative charge around CrOy unit formed via downsizing the cluster size has been proposed to account for favorable reduction of O22− and selective generation of reactive O−· radicals in small-sized (CrO3)1,2O− clusters. This study not only enriches the chemistry of metal-bonded O−· radicals toward alkane activation under mild conditions, but also provides a new insight into the conversion between O22− and O−· radicals over metal oxides. [ABSTRACT FROM AUTHOR]

Noble metals dispersed on transition-metal carbides exhibit extraordinary activity in CO2 catalytic conversion and bimetallic carbides generated at the interface were proposed to contribute to the observed activity. Heteronuclear metal carbide clusters (HMCCs) that compositionally resemble the bimetallic carbides are suitable models to get a fundamental understanding of the reactivity of the related condensed-phase catalysts, while the reaction of HMCCs with CO2 has not been touched in the gas phase. Herein, benefiting from the newly designed double ion trap reactors, the reaction of laser-ablation generated and mass-selected RhTaC2− clusters with CO2 was studied. The experimental results identified that RhTaC2− can reduce four CO2 molecules consecutively and generate the product RhTaC2O4−. The pivotal roles of Rh–Ta synergy and the C2 ligand in driving CO2 reduction were rationalized by theoretical calculations. The presence of an attached CO unit on the product RhTaC2O4− was evidenced by the collision-induced dissociation experiment, providing a fundamental strategy to alleviate carbon deposition under a CO2 atmosphere at elevated temperatures. [ABSTRACT FROM AUTHOR]

Catalytic co‐conversion of methane with carbon dioxide to produce syngas (2 H2+2 CO) involves complicated elementary steps and almost all the elementary reactions are performed at the same high temperature conditions in practical thermocatalysis. Here, we demonstrate by mass spectrometric experiments that RhTiO2− promotes the co‐conversion of CH4 and CO2 to free 2 H2+CO and an adsorbed CO (COads) at room temperature; the only elementary step that requires the input of external energy is desorption of COads from the RhTiO2CO− to reform RhTiO2−. This study not only identifies a promising active species for dry (CO2) reforming of methane to syngas, but also emphasizes the importance of temperature control over elementary steps in practical catalysis, which may significantly alleviate the carbon deposition originating from the pyrolysis of methane. [ABSTRACT FROM AUTHOR]

Direct conversion of methane with carbon dioxide to value‐added chemicals is attractive but extremely challenging because of the thermodynamic stability and kinetic inertness of both molecules. Herein, the first dinuclear cluster species, RhVO3−, has been designed to mediate the co‐conversion of CH4 and CO2 to oxygenated products, CH3OH and CH2O, in the temperature range of 393–600 K. The resulting cluster ions RhVO3CO− after CH3OH formation can further desorb the [CO] unit to regenerate the RhVO3− cluster, leading to the successful establishment of a catalytic cycle for methanol production from CH4 and CO2 (CH4+CO2→CH3OH+CO). The exceptional activity of Rh‐V dinuclear oxide cluster (RhVO3−) identified herein provides a new mechanism for co‐conversion of two very stable molecules CH4 and CO2. [ABSTRACT FROM AUTHOR]

Abstract: Catalytic CO oxidation by molecular O2 is an important model reaction in both the condensed phase and gas‐phase studies. Available gas‐phase studies indicate that noble metal is indispensable in catalytic CO oxidation by O2 under thermal collision conditions. Herein, we identified the first example of noble‐metal‐free heteronuclear oxide cluster catalysts, the copper–vanadium bimetallic oxide clusters Cu2VO3–5− for CO oxidation by O2. The reactions were characterized by mass spectrometry, photoelectron spectroscopy, and density functional calculations. The dynamic nature of the Cu−Cu unit in terms of the electron storage and release is the driving force to promote CO oxidation and O2 activation during the catalysis. [ABSTRACT FROM AUTHOR]

Abstract: The underlying mechanism for non‐oxidative methane aromatization remains controversial owing to the lack of experimental evidence for the formation of the first C−C bond. For the first time, the elementary reaction of methane with atomic clusters (FeC3−) under high‐temperature conditions to produce C−C coupling products has been characterized by mass spectrometry. With the elevation of temperature from 300 K to 610 K, the production of acetylene, the important intermediate proposed in a monofunctional mechanism of methane aromatization, was significantly enhanced, which can be well‐rationalized by quantum chemistry calculations. This study narrows the gap between gas‐phase and condensed‐phase studies on methane conversion and suggests that the monofunctional mechanism probably operates in non‐oxidative methane aromatization. [ABSTRACT FROM AUTHOR]

The hydrogenation of carbon dioxide involves the activation of the thermodynamically very stable molecule CO2 and formation of a C−H bond. Herein, we report that HCO2− and CO can be formed in the thermal reaction of CO2 with a diatomic metal hydride species, FeH−. The FeH− anions were produced by laser ablation, and the reaction with CO2 was analyzed by mass spectrometry and quantum-chemical calculations. Gas-phase HCO2− was observed directly as a product, and its formation was predicted to proceed by facile hydride transfer. The mechanism of CO2 hydrogenation in this gas-phase study parallels similar behavior of a condensed-phase iron catalyst. [ABSTRACT FROM AUTHOR]

Atomic clusters are being actively studied for activation of methane, the most stable alkane molecule. While many cluster cations are very reactive with methane, the cluster anions are usually not very reactive, particularly for noble metal free anions. This study reports that the reactivity of molybdenum carbide cluster anions with methane can be much enhanced by adsorption of CO. The Mo2C2− is inert with CH4 while the CO addition product Mo2C3O− brings about dehydrogenation of CH4 under thermal collision conditions. The cluster structures and reactions are characterized by mass spectrometry, photoelectron spectroscopy, and quantum chemistry calculations, which demonstrate that the Mo2C3O− isomer with dissociated CO is reactive but the one with non-dissociated CO is unreactive. The enhancement of cluster reactivity promoted by CO adsorption in this study is compared with those of reported systems of a few carbonyl complexes. [ABSTRACT FROM AUTHOR]

Investigations of the intrinsic properties of gas-phase transition metal nitride (TMN) ions represent one approach to gain a fundamental understanding of the active sites of TMN catalysts, the activities and electronic structures of which are known to be comparable to those of noble metal catalysts. Herein, we investigate the structures and reactivities of the triatomic anions HNbN− by means of mass spectrometry and photoelectron imaging spectroscopy, in conjunction with density functional theory calculations. The HNbN− anions are capable of activating CH4 and C2H6 through oxidative addition, exhibiting similar reactivities to free Pt atoms. The similar electronic structures of HNbN− and Pt, especially the active orbitals, are responsible for this resemblance. Compared to the inert NbN−, the coordination of the H atom in HNbN− is indispensable. New insights into how to replace noble metals with TMNs may be derived from this combined experimental/computational study. [ABSTRACT FROM AUTHOR]

Abstract: An experimental research on magnetic concentrate of a hematite using the anionic reverse flotation technology in the flotation column was conducted. Through systematic studies in the lab, the optimal technological and operational conditions had been obtained as follows: the circulation pressure of 0.055 MPa, the feeding quantity of 160 g/min, the collector dosage of 800 g/t and the starch dosage of 900 g/t. The results show that the iron concentrate with grade of 67.37% can be achieved according to the flow sheet of one roughing and one scavenging under the optimal conditions, and also reflects the advantages of excellent selectivity and high recovery. The application of cyclonic static micro-bubble flotation column in hematite reverse flotation provides a new approach for hematite reverse flotation in China. [Copyright &y& Elsevier]

Graphical abstract Sulfur‒oxygen exchange channels were observed in the reactions of oxygen atoms with CH 3 COS−, C 6 H 5 COS− and C 6 H 5 S− anions. Sulfur‒containing anions will be depleted in astrochemical environments where oxygen atoms are abundant. Highlights • None of the studied anions react with nitrogen atoms. • A sulfur‒oxygen exchange channel was observed in the reactions of oxygen atoms with CH 3 COS−, C 6 H 5 COS− and C 6 H 5 S− anions. • A sulfur abstraction channel was observed in the reactions of oxygen atoms with SCN− and −SCH 2 COOH anions. • The rate constants for reactions between sulfur‒containing anions and oxygen atoms are found to be higher than for the related oxygen‒containing anions. Abstract Sulfur‒containing anions are expected to exist in molecular clouds and other astrochemical environments due to the relative abundance of sulfur and the predicted stability of the anions. Furthermore, nitrogen and oxygen atoms are of high abundance in the interstellar medium. Therefore, reactions of nitrogen and oxygen atoms with small sulfur‒containing anions, SCN−, CH 3 COS−, C 6 H 5 COS−, −SCH 2 COOH, C 6 H 5 S−, and related oxygen‒containing anions, OCN−, CH 3 COO−, C 6 H 5 COO−, HOCH 2 COO−, C 6 H 5 O−, have been studied both experimentally and computationally. The experimental results show that none of the studied anions react with nitrogen atoms. All of the studied anions with the exception of OCN− react with oxygen atoms, and the reaction channels are more diverse than those for the previously studied reactions with hydrogen atoms. In addition to the associative electron detachment (AED) channel, some ionic products such as CN−, CH 3 COO−, C 6 H 5 COO−, HO− and S− were observed. A sulfur‒oxygen exchange channel was observed in the reactions of oxygen atoms with CH 3 COS−, C 6 H 5 COS− and C 6 H 5 S− anions. A sulfur abstraction channel was observed in the reactions of oxygen atoms with SCN− and −SCH 2 COOH anions. The rate constants for reactions between sulfur‒containing anions and oxygen atoms are found to be generally higher than for the related oxygen‒containing anions. Density functional theory calculations were conducted to provide insight into the experimental results. [ABSTRACT FROM AUTHOR]

Noble metals dispersed on transition-metal carbides exhibit extraordinary activity in CO2 catalytic conversion and bimetallic carbides generated at the interface were proposed to contribute to the observed activity. Heteronuclear metal carbide clusters (HMCCs) that compositionally resemble the bimetallic carbides are suitable models to get a fundamental understanding of the reactivity of the related condensed-phase catalysts, while the reaction of HMCCs with CO2 has not been touched in the gas phase. Herein, benefiting from the newly designed double ion trap reactors, the reaction of laser-ablation generated and mass-selected RhTaC2− clusters with CO2 was studied. The experimental results identified that RhTaC2− can reduce four CO2 molecules consecutively and generate the product RhTaC2O4−. The pivotal roles of Rh–Ta synergy and the C2 ligand in driving CO2 reduction were rationalized by theoretical calculations. The presence of an attached CO unit on the product RhTaC2O4− was evidenced by the collision-induced dissociation experiment, providing a fundamental strategy to alleviate carbon deposition under a CO2 atmosphere at elevated temperatures. [ABSTRACT FROM AUTHOR]

Laser ablation generated AuC3H–anionswere skimmed into a time-of-flight mass spectrometer (TOF-MS) andselected with a mass gate. Photoelectron spectra of AuC3H–were recorded using the velocity map imagingtechnique at several photon energies. The experimental spectra, quantumchemistry calculations, and Franck–Condon simulations suggestthat the AuC3H–cluster has four structureisomers, including one unexpected structure of [CCC–Au–H]−. When AuC3H–is comparedwith C3H2–, introduction ofgold into the hydrocarbon system results in the much lower isomerizationbarriers. [ABSTRACT FROM AUTHOR]

We present here a study of gas-phasereactivity of cobalt sulfidecluster anions ComSn–with molecular oxygen. Nascent ComSn–clusters were prepared via a laser ablation source and reacted withoxygen in a fast flow reactor under thermal collision conditions.We chose 18O2in place of 16O2to avoid mass degeneration with sulfur, and a time-of-flight(TOF) mass spectrometer was used to detect the cluster distributionsin the absence and presence of the reactant. It was found that oxygen–sulfurexchange occurs in the reactions for those with specific compositions(CoS)n–and (CoS)nS–(n=2–5) according to a consistent pathway, “ComSn– 18O2→ ComSn–118O– S18O”. Typically, for “Co2S2– 18O2”we have calculated the reaction coordinates by employing the densityfunctional theory (DFT), where both the oxygen–sulfur exchangeand SO molecule release are thermodynamically and kinetically favorable.It is noteworthy that the reaction with molecular oxygen (tripletground state) needs to overcome a spin excitation as well as a largeO–O activation energy. This study sheds light on the activationof molecular oxygen by cobalt sulfides on one hand and also providesinsight into the regeneration mechanism of cobalt oxides from thecounterpart sulfides in the presence of oxygen gas on the other hand. [ABSTRACT FROM AUTHOR]

Catalytic co‐conversion of methane with carbon dioxide to produce syngas (2 H2+2 CO) involves complicated elementary steps and almost all the elementary reactions are performed at the same high temperature conditions in practical thermocatalysis. Here, we demonstrate by mass spectrometric experiments that RhTiO2− promotes the co‐conversion of CH4 and CO2 to free 2 H2+CO and an adsorbed CO (COads) at room temperature; the only elementary step that requires the input of external energy is desorption of COads from the RhTiO2CO− to reform RhTiO2−. This study not only identifies a promising active species for dry (CO2) reforming of methane to syngas, but also emphasizes the importance of temperature control over elementary steps in practical catalysis, which may significantly alleviate the carbon deposition originating from the pyrolysis of methane. [ABSTRACT FROM AUTHOR]

Abstract: Catalytic CO oxidation by molecular O2 is an important model reaction in both the condensed phase and gas‐phase studies. Available gas‐phase studies indicate that noble metal is indispensable in catalytic CO oxidation by O2 under thermal collision conditions. Herein, we identified the first example of noble‐metal‐free heteronuclear oxide cluster catalysts, the copper–vanadium bimetallic oxide clusters Cu2VO3–5− for CO oxidation by O2. The reactions were characterized by mass spectrometry, photoelectron spectroscopy, and density functional calculations. The dynamic nature of the Cu−Cu unit in terms of the electron storage and release is the driving force to promote CO oxidation and O2 activation during the catalysis. [ABSTRACT FROM AUTHOR]

Vanadiumoxide cluster anions Vm16On–and Vm18On–were prepared by laser ablation and reacted withhydrogen sulfide (H2S) in a fast flow reactor under thermalcollision conditions. A time-of-flight mass spectrometer was usedto detect the cluster distributions before and after the interactionswith H2S. The experiments suggest that the oxygen-for-sulfur(O/S) exchange reaction to release water was evidenced in the reactorfor most of the cluster anions: VmOn– H2S →VmOn–1S– H2O. For reactions of clustersVO3–and VO4–with H2S, consecutive O/S exchange reactions led to thegeneration of sulfur containing vanadium oxide cluster anions VO3–kSk–(k= 1–3) and VO4–kSk–(k= 1–4). Density functional theory calculationswere performed for the reactions of VO3–4–with H2S, and the results indicate that the O/S exchangereactions are both thermodynamically and kinetically favorable, whichsupports the experimental observations. The reactions of VmOn牛겵cations with H2S have been reported previously (Jia, M.-Y.; Xu, B.; Ding, X.-L.; Zhao, Y.-X.; He, S.-G.; Ge, M.-F.J. Phys. Chem. C2012, 116, 9043), and this study of cluster anionsprovides further new insights into the transformations of H2S over vanadium oxides at the molecular level. [ABSTRACT FROM AUTHOR]

Review: study of gas phase reactions by state-of-the-art mass spectrometric experimentin conjunction with quantum chemical calculations; 248 refs. [ABSTRACT FROM AUTHOR]