Vanadium Clusters Research Articles

Crystal-Plane-Engineered TiO2-Anchored Vanadium Single Atoms and Clusters for Boosting Ultradeep Aerobic Oxidative Desulfurization of Diesel.

The crystal plane effect has gained extensive attention in heterogeneous catalysis reactions; however, it is far from being systematically probed in titanium dioxide (TiO2)-supported vanadium catalysts. Herein, a series of vanadium (V) single atoms and clusters anchored on TiO2 with different crystal planes was fabricated by an improved "top-down" protocol. The dispersion state, electronic structure, and redox properties of the V single-atom and VOx cluster-supported catalysts were systematically analyzed by a series of characterization methods, including X-ray absorption near edge structure (XANES) and density functional theory (DFT) calculations, and their catalytic performances were examined for aerobic oxidative desulfurization (AODS) of 4,6-dimethyl-dibenzothiophen (4,6-DMDBT) with O2 as the oxidant. The results unveiled that the synergistic effect between the V single atom and the VOx cluster perceptibly promoted the catalytic performances of VOx/TiO2 samples. Therein, VOx/TiO2-(001) shows the lowest apparent activation energy (Ea) value of 46.3 kJ/mol and the optimal AODS performance with complete 4,6-DMDBT conversion to 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO2) within 60 min at 120 °C as compared with VOx/TiO2-(101) (81.9 kJ/mol and 180 min) and VOx/TiO2-(100) (68.0 kJ/mol and 240 min), which should be attributed to its higher V5+/V4+ ratio, the optimal redox behavior of the V species, the moderate adsorption energy between 4,6-DMDBT and VOx active centers, and the synthetic effect of V single atoms and VOx clusters. Moreover, VOx/TiO2-(001) exhibits robust durability in seven cycles of reuse, showcasing the potential for practical applications in the future.

Effects of the tetravanadate [V4O12]4− anion on the structural, magnetic, and biological properties of copper/phenanthroline complexes

The aim to access linked tetravanadate [V4O12]4− anion with mixed copper(II) complexes, using α-amino acids and phenanthroline-derived ligands, resulted in the formation of four copper(II) complexes [Cu(dmb)(Gly)(OH2)]2[Cu(dmb)(Gly)]2[V4O12]·9H2O (1) [Cu(dmb)(Lys)]2[V4O12]·8H2O (2), [Cu(dmp)2][V4O12]·C2H5OH·11H2O (3), and [Cu(dmp)(Gly)Cl]·2H2O (4), where dmb = 4,4′-dimethioxy-2,2′-bipyridine; Gly = glycine; Lys = lysine; and dmp = 2,9-dimethyl-1,10-phenanthroline. The [V4O12]4− anion is functionalized with mixed copper(II) units in 1 and 2; while in 3, it acts as a counterion of two [Cu(dmp)]2+ units. Compound 4 crystallized as a unit that did not incorporate the vanadium cluster. All compounds present magnetic couplings arising from Cu⋯O/Cu⋯Cu bridges. Stability studies of water-soluble 3 and 4 by UV–Vis spectroscopy in cell culture medium confirmed the robustness of 3, while 4 appears to undergo ligand scrambling over time, resulting partially in the stable species [Cu(dmp)2]+ that was also identified by electrospray ionization mass spectrometry at m/z = 479. The in vitro cytotoxicity activity of 3 and 4 was determined in six cancer cell lines; the healthy cell line COS-7 was also included for comparative purposes. MCF-7 cells were more sensitive to compound 3 with an IC50 value of 12 ± 1.2 nmol. The tested compounds did not show lipid peroxidation in the TBARS assay, ruling out a mechanism of action via reactive oxygen species formation. Both compounds inhibited cell migration at 5 µM in wound-healing assays using MCF-7, PC-3, and SKLU-1 cell lines, opening a new window to study the anti-metastatic effect of mixed vanadium–copper(II) systems.Graphical abstract

New Multicomponent Optimization Scheme for Equiatomic Vanadium-Titanium Nanoparticle Study.

We present a new multicomponent structure prediction method named MRS-Swap searching, which is inspired by space symmetry and swap of different atomic species. For the pure titanium cluster, a new ground-state structure of the Ti20 cluster with higher symmetry relative to a previous study was found by our method. Based on the structural analysis of Tin (n = 2k, k = 2-11), Vn (n = 2k, k = 2-11), and TinVm (n = m = 2-11) systems, we found that the lowest energy structures of these three systems are very similar, which indicates that equiatomic vanadium-titanium-mixed clusters do not change their ground-state structure relative to the same size pure vanadium and titanium cluster. According to the structure-activity relationship, we conclude that the yield strength (σ) of macro vanadium-titanium alloy is between pure titanium and pure vanadium metal, and this can be expressed through σ(Ti) > σ(TiV) > σ(V). The X-ray diffraction results show that the V2Nb, TiVNb, and Ti2Nb alloys also have the same BCC structure, which may be related to their microstructure. Our method and results can be helpful for future multicomponent alloy design.

Probing adsorption of methane onto vanadium cluster cations via vibrational spectroscopy.

Photofragment spectroscopy is used to measure the vibrational spectra of V2+(CH4)n (n = 1-4), V3+(CH4)n (n = 1-3), and Vx+(CH4) (x = 4-8) in the C-H stretching region (2550-3100 cm-1). Spectra are measured by monitoring loss of CH4. The experimental spectra are compared to simulations at the B3LYP+D3/6-311++G(3df,3pd) level of theory to identify the geometry of the ions. Multi-reference configuration interaction with Davidson correction (MRCI+Q) calculations are also carried out on V2+ and V3+. The methane binding orientation in V2+(CH4)n (n = 1-4) evolves from η3 to η2 as more methane molecules are added. The IR spectra of metal-methane clusters can give information on the structure of metal clusters that may otherwise be hard to obtain from isolated clusters. For example, the V3+(CH4)n (n = 1-3) experimental spectra show an additional peak as the second and third methane molecules are added to V3+, which indicates that the metal atoms are not equivalent. The Vx+(CH4) show a larger red shift in the symmetric C-H stretch for larger clusters with x = 5-8 than for the small clusters with x = 2, 3, indicating increased covalency in the interaction of larger vanadium clusters with methane.

Hydrogen Storage Mechanism by Gas-Phase Vanadium Cluster Cations Revealed by Thermal Desorption Spectrometry.

The adsorption of hydrogen on gas-phase vanadium cluster cations, Vn+ (n = 3-14), at 300 K and desorption of hydrogen from hydride clusters, VnHm+, upon heating were observed experimentally by combined thermal desorption spectrometry and mass spectrometry analyses. The ratio m/n was approximately 1.3 for all n values at 300 K, which was reduced to approximately zero at 1000 K. For n = 4, stable cluster geometries of V4Hm+ (m = 0, 2, 4, and 6) were investigated by DFT calculations, revealing that V4 adopted a trigonal pyramidal structure and the H atoms adsorbed mainly on the μ2 bridge sites. The adsorption reaction pathway of one H2 molecule on V4+ was also investigated. The experimentally estimated desorption energies of the H2 molecules were consistent with their calculated binding energies. Among the observed hydride clusters, V6H8+ was found to be significantly thermally durable, probably because of its close-packed octahedral V6 core structure, with H atoms occupying all hollow sites.

Revealing the Minimum Energy Pathways for Formamide Hydrogenation Reactions in the Presence of Platinum and Platinum–Vanadium Clusters: A Quantum Chemical DFT/Nudged Elastic Band Study

A detailed study on the stages of catalytic reactions involving platinum and platinum-vanadium clusters has been carried out. Minimum energy pathways (MEP) of reactions have been constructed via the DFT/PBE0/def2tzvp method using NEB functional and optimized structures, and points of minima and transition states have been calculated. A two-step process for the conversion of formamide to methylamine under the action of H2 has been considered as a test reaction. The energy barriers of this reaction, not previously described in the literature, have been evaluated. It has been shown that the main changes in the structural characteristics of the reagents, as well as the migration of single H atoms from one metal center of clusters to another or to an organic substrate, are initiated at the molecular level by shifts corresponding to the vectors of normal vibrations of systems in transition states.

Green Oxidation of Isochromans to Isochromanones with Molecular Oxygen Catalyzed by a Tetranuclear Vanadium Cluster

Comprehensive SummaryIsochromanone is the core structure of many bioactive compounds. Direct oxidation of isochromans is one of leading methods for the construction of isochromanones, while most established processes remain suffering from the use of environmentally unfriendly metal oxidants, harsh reaction conditions, and the difficulty in catalyst recycling and product separation. Herein, we report a convenient, cost‐effective, and green method for the synthesis of high‐value added isochromanones via isochroman oxidations with O2 by a novel heterogeneous vanadium cluster catalyst (Cat.1) under mild conditions. This reaction protocol demonstrates high catalytic activity with good catalyst recyclability and reusability for a wide scope of substrates.

Efficient iodine capture by metal–organic cubes based on hexanuclear vanadium clusters

Two isostructural metal–organic cubes were self-assembled from large-sized tetradentate ligand constructs with hexanuclear vanadium clusters. They have excellent iodine vapor adsorption properties due to large cavities and host–guest interactions.

Vanadium‐based metal‐organic frameworks and their derivatives for electrochemical energy conversion and storage

AbstractWith the excessive consumption of nonrenewable resources, the exploration of effective and durable materials is highly sought after in the field of sustainable energy conversion and storage system. In this aspect, metal‐organic frameworks (MOFs) are a new class of crystalline porous organic‐inorganic hybrid materials. MOFs have recently been gaining traction in energy‐related fields. Owing to the coordination flexibility and multiple accessible oxidation states of vanadium ions or clusters, vanadium‐MOFs (V‐MOFs) possess unique structural characteristics and satisfactory electrochemical properties. Furthermore, V‐MOFs‐derived materials also exhibit superior electrical conductivity and stability when used as electrocatalysts and electrode materials. This review summarizes the research progress of V‐MOFs (inclusive of pristine V‐MOFs, V/M‐MOFs, and POV‐based MOFs) and their derivatives (vanadium oxides, carbon‐coated vanadium oxide, vanadium phosphate, vanadate, and other vanadium doped nanomaterials) in electrochemical energy conversion (water splitting, oxygen reduction reaction) and energy storage (supercapacitor, rechargeable battery). Future possibilities and challenges for V‐MOFs and their derivatives in terms of design and synthesis are discussed. Lastly, their applications in energy‐related fields are also highlighted.

Four novel Z-shaped hexanuclear vanadium oxide clusters as efficient heterogeneous catalysts for cycloaddition of CO2 and oxidative desulfurization reactions

Chemical fixation of CO2 into C1 source, as a general approach, can effectively alleviate the emission of greenhouse gasses. Whereas, the challenge posed by the need for efficient catalysts with high catalytic active sites still exists. In this work, we reported a series of new hexavanadate clusters, [(C6H6ON)2(C2H8N2)2(CH3O)6VIV6O8] (V6–1), [(C6H6ON)2(C3H10N2)2(CH3O)6VIV6O8] (V6–2), [(C6H6ON)2(C6H14N2)2(CH3O)6VIV6O8] (V6–3) and [(C6H6ON)2(C4H11N2O)2(CH3O)4VIV6O8] (V6–4), assembled by 2-aminophenol and four different kinds of Lewis bases (LB), ethanediamine (en), 1,2-diaminopropane, 1,2-cyclohexanediamine and N-(2-hydroxyethyl)ethylenediamine (ben) together. Among them, the basic unit {V6} cluster featured Z-shaped configuration represents a brand-new example of hexanuclear vanadium clusters. Remarkably, the catalytic tests demonstrated that V6–1 as catalyst displays high catalytic activity in the cycloaddition for the CO2 fixation into cyclic carbonates by virtue of open V sites. As expected, for oxidative desulfurization of sulfides, V6–1 also exhibits satisfied catalytic effectiveness. Furthermore, the recycling test confirmed that catalyst V6–1 may be a bifunctional heterogeneous catalyst with great promise for both CO2 cycloaddition and oxidative desulfurization reactions.

A systematic analysis of phase stability in refractory high entropy alloys utilizing linear and non-linear cluster expansion models

The phase segregation behavior of three key refractory high entropy alloys (NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr) is studied using first-principles calculations. Several linear and non-linear methods are utilized to generate surrogate models for three key refractory high entropy alloys (NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr) via the cluster expansion formalism. The characteristics of each of the generated models is explored and the regression methods are compared. Finally, these surrogate models are utilized to generate Monte Carlo trajectories in order to explore the link between phase segregation and previously documented mechanical degradation in these materials.Phase segregation and intermetallic phases documented in the experimental literature are reproduced in all three high entropy alloys. NbTiVZr forms vanadium and zirconium clusters at lower temperatures (250 K) which disperse into the single-phase matrix by 1000 K. HfNbTaTiZr forms HfZr, NbTa, and possibly TiZr intermetallic phases at lower temperatures (250 K). Unlike the other HEAs studied here, HfNbTaTiZr does not lose short-range ordering in the solid state until around 3500 K, which is above its melting temperature. AlHfNbTaTiZr forms NbTa and AlHfTiZr phases at lower temperatures (250 K), which are not observed at higher temperatures (1000 K).

One Functionalized Polyoxovanadates Hybrid Material Based on Arsonic Acid with Highly Effective Catalytic Property of Sulfides

In this work, a novel 4-aminophenylarsonic acid functionalized polyoxovanadates (POVs) hybrid material, namely, (Me2NH2)4 ·[(L)8(H12V16O32)] (H2L = 4-NH2C6H4AsO3H2) POVs 1 was solvothermally synthesized and fully characterized. The results revealed POVs 1 consists of four similar tetranuclear vanadium clusters bridged by eight organic 4-aminophenylarsonic acid ligands. Remarkably, functionalized hybrid POVs 1 was further investigated as a heterogeneous stable catalyst in oxidation of sulfide derivatives, and exhibited high catalytic activities (yields up to 96.7%). Additionally, the functionalized hybrid polyoxovanadates catalyst can be reused without losing activities after three runs cycle.

Vanadium Cluster Neutrals Reacting with Water: Superatomic Features and Hydrogen Evolution in a Fishing Mode.

Hydrogen evolution reaction (HER) is known as the heart of various energy storage and conversation systems of renewable energy sources. Here we observe the cluster reactions of a light transition metal, vanadium, with water in a gas-phase flow tube reactor. While HER products of V1 and V2 were not observed, the effective HER of water on neutral Vn (n ≥ 3) clusters reveals reasonable and size-dependent reactivity of the vanadium clusters. Superatomic features and reaction dynamics of V10, V13, and V16 are highlighted. Among the three typical superatoms, V10 and V16 exhibit an abnormal superatomic orbital energy level order, 1S|2S|1P|1D..., where the energy-reduced 2S orbital helps to accommodate the geometric structure and hence reinforce the cluster stability. In comparison, V13 bears a less symmetrical structure and reacts readily with water, allowing for recombination of a hydroxyl atom with an adsorbed hydrogen atom, akin to a fishing-mode HER process. The joint experimental and theoretical study on neutral Vn clusters clarifies the availability of superatom chemistry for transition metals and appeals further development of cluster theory based on electronic cloud/orbital analysis instead of simply counting the valence electrons. Also, we provide insights into the HER mechanism of metal clusters and propose a strategy to design new materials for portable fuel cells of hydrogen energy.

Hollow Lindqvist-like-Shaped {V6} Cluster-Based Metal-Organic Framework for the Highly Efficient Detoxification of Mustard Gas Simulant.

A polyoxovanadate-based nickel-organic framework, [Ni(bib)2]{V2O6}({V6}-MOF, bib = 1,4-bis(1H-imidazoly-1-yl)benzene), was facilely prepared under gentle hydrothermal conditions and structurally characterized. Single-crystal X-ray diffraction analysis indicates that the {V6} cluster in the {V6}-MOF is constructed of two VO5 tetragonal pyramids and four VO4 tetrahedrons via the apex sharing of O atoms, presenting a hollow Linqvist-like structure, which is different from these reported hexanuclear vanadium clusters. The {V6}-MOF not only expands the structure of polyoxovanadates (POVs) but also catalyzes the rapid detoxification of mustard gas simulant (2-chloroethyl ethyl sulfide, CEES) at 25 °C. The catalytic results were determined by means of GC, GC-MS, and 1H NMR. Using {V6}-MOF as a heterogeneous catalyst, CEES underwent catalyzed oxidation to only nontoxic product 2-chloroethyl ethyl sulfoxide (CEESO) within 40 min, and the conversion and selectivity were almost 100%. In addition, {V6}-MOF exhibits high sustainability, and no obvious reductions in conversion and selectivity are observed after five runs.

Observation of the Reaction Intermediates of Methanol Dehydrogenation by Cationic Vanadium Clusters

AbstractA mass spectrometric study of the reactions of vanadium cationic clusters with methanol in a low‐pressure collision cell is reported. For comparison, the reaction of methanol with cobalt cationic clusters was studied. For vanadium, the main reaction products are fully dehydrogenated species, and partial dehydrogenation and non‐dehydrogenation species are observed as minors, for which the relative intensities increase with cluster size and also at low cluster source temperature cooled by liquid nitrogen; no dehydrogenation products were observed for cobalt clusters. Quantum chemical calculations explored the reaction pathways and revealed that the fully dehydrogenation products of the reaction between Vn+ and methanol are Vn(C)(O)+, in which C and O are separated owing to the high oxophilicity of vanadium. The partial dehydrogenation and non‐dehydrogenation species were verified to be reaction intermediates along the reaction pathway, and their most probable structures were proposed.

Observation of the Reaction Intermediates of Methanol Dehydrogenation by Cationic Vanadium Clusters.

A mass spectrometric study of the reactions of vanadium cationic clusters with methanol in a low-pressure collision cell is reported. For comparison, the reaction of methanol with cobalt cationic clusters was studied. For vanadium, the main reaction products are fully dehydrogenated species, and partial dehydrogenation and non-dehydrogenation species are observed as minors, for which the relative intensities increase with cluster size and also at low cluster source temperature cooled by liquid nitrogen; no dehydrogenation products were observed for cobalt clusters. Quantum chemical calculations explored the reaction pathways and revealed that the fully dehydrogenation products of the reaction between Vn + and methanol are Vn (C)(O)+ , in which C and O are separated owing to the high oxophilicity of vanadium. The partial dehydrogenation and non-dehydrogenation species were verified to be reaction intermediates along the reaction pathway, and their most probable structures were proposed.

A Systematic Analysis of Phase Stability in Refractory High Entropy Alloys Utilizing Linear and Non-Linear Cluster Expansion Models

The phase segregation behavior of three key refractory high entropy alloys (NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr) is studied using first-principles calculations. Several linear and non-linear methods are utilized to generate surrogate models for three key refractory high entropy alloys (NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr) via the cluster expansion formalism. The characteristics of each of the generated models is explored and the regression methods are compared. Finally, these surrogate models are utilized to generate Monte Carlo trajectories in order to explore the link between phase segregation and previously documented mechanical degradation in these materials.Phase segregation and intermetallic phases documented in the experimental literature are reproduced in all three high entropy alloys. NbTiVZr forms vanadium and zirconium clusters at lower temperatures (250 K) which disperse into the single-phase matrix by 1000 K. HfNbTaTiZr forms HfZr, NbTa, and possibly TiZr intermetallic phases at lower temperatures (250 K). Unlike the other HEAs studied here, HfNbTaTiZr does not lose short-range ordering in the solid state until around 3500 K, which is above its melting temperature. AlHfNbTaTiZr forms NbTa and AlHfTiZr phases at lower temperatures (250 K), which are not observed at higher temperatures (1000 K).

An oxygen-passivated vanadium cluster [V@V10O15]- with metal-metal coordination produced by reacting Vn- with O2.

Vanadium cluster anions are highly reactive making the preparation of pure Vn- and the observation of their reactivity extremely challenging. Herein, well-resolved anionic Vn- clusters are prepared enabling an in-depth study on their reactions with O2 in the gas phase. While pure metal clusters of a magic number are not identified due to the strong V-O bonding, interestingly an unexpected oxide V11O15- was experimentally observed in surviving O2 etching reactions. First-principles theory calculations indicate that V11O15- possesses a body-centered pentagonal prism structure (D5h, ), with the V@V10 core fully protected by 15 oxygen bridges. Such an oxygen-protected metal cluster [V@V10O15]- exhibits typical superatom orbital features pertaining to the V@V10 core which shows effective metal-metal coordination bonding. Meanwhile, the high stability of [V@V10O15]- is reinforced by the V-O-V conjugation interactions which help to maintain the structural integrity, resulting in 3D inorganic aromaticity. This finding of such an oxygen-passivated superatom cluster sheds light on the bonding nature in ligand-protected metal clusters via wet synthesis.

Tandem-like vanadium cluster chains in a polyoxovanadate-based metal–organic framework for efficient catalytic oxidation of sulfides

The vanadium cluster chain in V-Ni-MOF can efficiently catalyze the oxidation of sulfides with hydrogen peroxide as the oxidant, achieving the complete conversion from sulfides to sulfones within 1 hour at 40 °C.

Initial Steps in the Selective Catalytic Reduction of NO with NH3 by TiO2-Supported Vanadium Oxides

Electronic structure calculations at the density functional theory/B3LYP level (selectively benchmarked by CCSD(T)) were performed on neutral and protonated monomer and dimer clusters of vanadium o...