On the origin of the surprisingly sluggish redox reaction of the N2O/CO couple mediated by [Y2O2]+˙ and [YAlO2]+˙ cluster ions in the gas phase

Reactivity of Atomic Oxygen Radical Anions in Metal Oxide Clusters

Atomic oxygen radical anion (O⋅-) represents an important type of reactive centre that exists in both chemical and biological systems. Gas-phase atomic clusters can be studied under isolated and well controlled conditions. Studies of O⋅--containing clusters in the gas-phase provide a unique strategy to interpret the chemistry of O⋅- radicals at a strictly molecular level. This review summarizes the research progresses made since 2013 for the reactivity of O⋅- radicals in the atomically precise metal oxide clusters including negatively charged, nanosized, and neutral heteronuclear metal clusters benefitting from the development of advanced experimental techniques. New electronic and geometric factors to control the reactivity and product selectivity of O⋅- radicals under dark and photo-irradiation conditions have been revealed. The detailed mechanisms of O⋅- generation have been discussed for the reaction systems of nanosized and heteroatom-doped metal oxide clusters. The catalytic reactions mediated by the O⋅- radicals in metal clusters have also been successfully established and the microscopic mechanisms about the dynamic generation and depletion of O⋅- radicals have been clearly understood. The studies of O⋅- containing metal oxide clusters in the gas-phase provided new insights into the chemistry of reactive oxygen species in related condensed-phase systems.

Structural and photoelectron spectroscopic study on the heterotrinuclear nickel-titanium dioxide carbonyl complexes Ni2TiO2(CO) n - (n = 2-4)

Herein, the configurations and intrinsic electronic properties of heteronuclear transition metal dioxide carbonyl anions Ni₂TiO₂(CO) _n ^- (n = 2-4) in the gas phase were investigated using mass spectrometry coupled anionic photoelectron spectroscopy, ab initio calculations, and simulated density-of-state (DOS) spectra. The results clearly show that the binding of electrons is enhanced by the addition of CO. The ground state structures of Ni₂TiO₂(CO) _n ^- (n = 2-4) are characterized to show that three transition metal atoms (one Ti atom and two Ni atoms) forming a quasi-line is favored. The interaction between Ni and C becomes weaker as the cluster size increases. The natural electron configuration shows that the extra electron is enriched on O atoms attached to Ti, and there is strong interaction between Ti and O atoms. This work gives significant insight into the configuration and electronic structures of nickel-titanium dioxide carbonyl anions, which has potential application in adsorption of carbon monoxide on the surfaces/interfaces of alloys.

Experimental and Theoretical Study of N2 Adsorption on Hydrogenated Y2C4H− and Dehydrogenated Y2C4− Cluster Anions at Room Temperature

The adsorption of atmospheric dinitrogen (N₂) on transition metal sites is an important topic in chemistry, which is regarded as the prerequisite for the activation of robust N≡N bonds in biological and industrial fields. Metal hydride bonds play an important part in the adsorption of N₂, while the role of hydrogen has not been comprehensively studied. Herein, we report the N₂ adsorption on the well-defined Y₂C₄H_0,1⁻ cluster anions under mild conditions by using mass spectrometry and density functional theory calculations. The mass spectrometry results reveal that the reactivity of N₂ adsorption on Y₂C₄H⁻ is 50 times higher than that on Y₂C₄⁻ clusters. Further analysis reveals the important role of the H atom: (1) the presence of the H atom modifies the charge distribution of the Y₂C₄H⁻ anion; (2) the approach of N₂ to Y₂C₄H⁻ is more favorable kinetically compared to that to Y₂C₄⁻; and (3) a natural charge analysis shows that two Y atoms and one Y atom are the major electron donors in the Y₂C₄⁻ and Y₂C₄H⁻ anion clusters, respectively. This work provides new clues to the rational design of TM-based catalysts by efficiently doping hydrogen atoms to modulate the reactivity towards N₂.

Structural assignments of yttrium oxide cluster cations studied by ion mobility mass spectrometry

The geometric structures of yttrium oxide cluster ions, Y_nO_m⁺ (n = 3-11), were experimentally assigned for stable compositions by ion mobility mass spectrometry combined with theoretical calculations. The stable compositions were firstly determined by collision induced dissociation experiments in mass spectrometry as YO(Y₂O₃)_x⁺ and YO₂(Y₂O₃)_x⁺ for odd numbers of Y atoms (n = 2x + 1) and (Y₂O₃)_x⁺ and O(Y₂O₃)_x⁺ for even numbers of Y atoms (n = 2x). The structures of the ions with the above compositions were assigned by comparing the collision cross sections obtained in the ion mobility measurement with those obtained by theoretical calculations. The assigned structures have the following two characteristic features. Firstly, metal-metal or oxygen-oxygen bonds were rarely observed, and most of the oxygen atoms bridge two Y atoms, which is due to the ionic bonding nature between Y³⁺ and O^2- ions. Secondly, common Y-atom frameworks were obtained for the ions with the same number of Y atoms n. For example, for the clusters with even numbers of Y atoms, one atomic oxygen radical anion (O^-) in the most stable structures of (Y₂O₃)_x⁺ was replaced with a superoxide ion (O₂^-) to form the most stable structures of O(Y₂O₃)_x⁺ ions, keeping the Y-atom framework geometries.

Tetrahedral Pt10- Cluster with Unique Beta Aromaticity and Superatomic Feature in Mimicking Methane

Utilizing a customized metal cluster source in tandem with a flow tube reactor and a reflectron time-of-flight mass spectrometer, we have obtained well-resolved pure metal clusters Pt_n^- and observed their gas-phase reactions with a few small gas molecules. Interestingly, the remarkable inertness of Pt₁₀^- was repeatedly observed in different reactions. Meanwhile, we have determined the structure of Pt₁₀^- within a regular tetrahedron. Considering that Pt possesses 5d⁹6s¹ electron configuration, the tetrahedral Pt₁₀^- exhibits unexpected stability at neither a magic number of valence electrons nor a shell closure of geometric structure. Comprehensive theoretical calculations unveil the stability of Pt₁₀^- is significantly associated with the all-metal aromaticity. In addition to the classical total aromaticity, which is mainly due to 6s electrons, there is unique beta-aromaticity ascribed to spin-polarized beta 5d electrons pertaining to singly occupied multicenter bonds. Further, we demonstrate the superatomic feature of such a transition metal cluster Pt₁₀^-, as Pt₆@Pt₄^-, in mimicking methane.

Neutral noble-metal-free VCoO2 and CrCoO2 cluster catalysts for CO oxidation by O2

Neutral noble-metal-free metal oxide cluster catalysts (VCoO₂ and CrCoO₂) were developed for multiple CO oxidation reactions by O₂.

Ligand-Mediated Reactivity in CO Oxidation of Niobium-Nickel Monoxide Carbonyl Complexes: The Crucial Roles of the Multiple Adsorption of CO Molecules

The heteronuclear metal oxide complexes are of great significance in heterogeneous catalytic oxidation of CO. However, previous studies are mainly focused on the composition of metal oxide, charge state, the support and the active oxygen species, with little attention paid to adsorbed CO ligands. Herein, the ligand-mediated reactivity in CO oxidation of niobium-nickel monoxide carbonyl complexes has been successfully identified. The NbNiO(CO) _n^- ( n = 5-6) anions are determined to be O-bridged complexes. In contrast, the NbNiO(CO) _n^- ( n = 7-8) anions are characterized to be η²-CO₂-tagged complexes. The crucial roles of the multiply adsorbed CO molecules that can facilitate not only the competitive binding with bridging oxygen atom to the transition metal centers but also the electron accumulation of transition metal atoms have been discovered. The fascinating results are of substantial importance to understand the mechanisms of CO oxidation over heteronuclear metal oxide under CO-rich feed condition.

DFT Study of the Spin-Forbidden Reaction of N2O with CO Catalysed by Y+ Ions

The mechanism of the cyclic reaction N2O(X1Σ+) + CO(1Σ+) → N2(X1Σg+) + CO2(1Σg+) catalysed by Y+ ions has been investigated on both singlet and triplet potential energy surfaces. The reactions were investigated by means of the relativistic effective core potential together with the Stuttgart basis sets on Y and the UB3LYP/6-311G** level of theory on non-metal atoms. The crossings involved between the singlet and triplet energy surfaces have been investigated by means of the intrinsic reaction coordinate approach used by Yoshizawa et al. Furthermore, both steps of the reaction are exothermic and the overall reaction is exothermic by 361.12 kJ mol−1.

Computational study for the circular redox reaction of N2O with CO catalyzed by fullerometallic cations C60Fe+ and C70Fe<sup/>

We applied density functional calculations to study the circular redox reaction mechanism of N₂O with CO catalyzed by fullerometallic cations C₆₀Fe⁺ and C₇₀Fe⁺. The on-top sites of six-membered rings (η⁶) of fullerene cages are the most preferred binding sites for Fe⁺ cation, and the hexagon to pentagon migration of Fe⁺ is unlikely under ambient thermodynamic conditions. The initial ion/molecule reaction, N₂O rearrangement and N₂ abstraction on the considered fullerometallic cations are easier than those on the bare Fe⁺ cation in the gas phase. Generally, our results indicate that fullerometallic ions, C₆₀Fe⁺ and C₇₀Fe⁺, are more favorable substrates for redox reaction of N₂O with CO in comparison to the other previously studied carbon nanostructures such as graphene and nanotubes.

Ménage-à-trois: single-atom catalysis, mass spectrometry, and computational chemistry

Genuine, single-atom catalysis can be realized in the gas phase and probed by mass spectrometry combined with computational chemistry.

The reactivity of stoichiometric tungsten oxide clusters towards carbon monoxide: the effects of cluster sizes and charge states

Density functional theory (DFT) calculations are employed to investigate the reactivity of tungsten oxide clusters towards carbon monoxide. Extensive structural searches show that all the ground-state structures of (WO3)n(+) (n = 1-4) contain an oxygen radical center with a lengthened W-O bond which is highly active in the oxidation of carbon monoxide. Energy profiles are calculated to determine the reaction mechanisms and evaluate the effect of cluster sizes. The monomer WO3(+) has the highest reactivity among the stoichiometric clusters of different sizes (WO3)n(+) (n = 1-4). The reaction mechanisms for CO with mono-nuclear stoichiometric tungsten oxide clusters with different charges (WO3(-/0/+)) are also studied to clarify the influence of charge states. Our calculated results show that the ability to oxidize CO gets weaker from WO3(+) to WO3(-) as the negative charge accumulates progressively.

Catalytic oxidation of CO with N2O on isolated copper cluster anions

A catalytic redox reaction involving N2O and CO on size-selected copper cluster anions, Cun(-), was investigated in the gas phase using a guided ion-beam tandem mass spectrometer. When Cun(-) is exposed to a mixture of N2O and CO, CunO(-) is produced via the decomposition of N2O. Increase of the CO partial pressure results in the reproduction of Cun(-) and decrease of CunO(-) through the oxidation of CO. The present results demonstrate that a full catalytic cycle for the reaction, N2O + CO → N2 + CO2, takes place on copper cluster anions. Furthermore, in the investigations of the elementary reactions of Cun(-) + N2O and CunO(-) + CO, we found that the catalytic oxidation of CO with N2O on Cun(-) proceeds most efficiently at n = 7 in the size range of n = 5-16.

Synthetic chemistry with nitrous oxide

Nitrous oxide (N₂O, ‘laughing gas’) is a very inert molecule. Still, it can be used as a reagent in synthetic organic and inorganic chemistry, serving as O-atom donor, as N-atom donor, or as a oxidant in metal-catalyzed reactions.

Catalytic oxidation of CO by N2O on neutral Y2MO5 (M = Y, Al) clusters: a density functional theory study

The full catalytic cycle of CO oxidation by N₂O on neutral Y₂MO₅ (M = Y, Al) clusters has been studied in the current work.

Gas-phase reaction of CeVO5+ cluster ions with C2H4: the reactivity of cluster bonded peroxides

The reactivity of the peroxide unit with hydrocarbon molecules on transition metal oxide clusters with a closed-shell electronic structure has been identified for the first time.

CO Oxidation Promoted by Gold Atoms Loosely Attached in AuFeO3(-) Cluster Anions

Time-of-flight mass spectrometry experiment shows that upon the interactions with carbon monoxide, the mass-selected AuFeO3(-) oxide cluster anions can evaporate neutral gold atoms in a hexapole collision cell and oxidize CO into CO2 in an ion trap reactor. The computational studies identify that the gold atom is loosely attached in the AuFeO3(-) cluster, and the different reaction channels can be attributed to different cluster velocities. The structure of the AuFeO3(-) cluster is very flexible, and the approach of CO induces significant geometrical and electronic structure changes of AuFeO3(-), which facilitates the exposure of the positively charged gold atom to trap and oxidize CO. The CO oxidation by the AuFeO3(-) cluster follows the Au-assisted Mars-van Krevelen mechanism, in which the direct participation of the surface lattice oxygen (O(2-)) is proposed.

Structural evolution, sequential oxidation and chemical bonding in tri-yttrium oxide clusters: Y3Ox− and Y3Ox (x = 0–6)

The evolution of regularities for Y₃O_x^−/0 (x = 0–6) and all-metal aromaticity of the Y₃⁻ cluster have been discovered.