Mo Clusters Research Articles

DFT-D3 Study of Molecular N2 and H2 Activation on Co3Mo3N Surfaces

Cobalt molybdenum nitride (Co3Mo3N) is one of the most active catalysts for ammonia synthesis, although the atomistic details of the reaction mechanism are currently unknown. We present a dispersion-corrected (D3) DFT study of the adsorption and activation of molecular nitrogen and hydrogen on Co3Mo3N-(111) surfaces to identify possible activation sites for ammonia synthesis. H2 was found to adsorb both molecularly on the Mo3N framework and dissociatively on Co8 clusters or Mo3 clusters that were exposed due to N-vacancies. We find that there are two possible activation sites for N2 where both N2 and H2 can coadsorb. The first is a Mo3 triangular cluster that resides at 3f nitrogen vacancies, and the second is a surface cavity where N2 is activated by a Co8 cluster, the second being a more efficient activation site. N2 was found to adsorb in three adsorption configurations: side-on, end-on, and an unusual tilt end-on (155°) configuration, and the existence of these three adsorption configurations is expla...

Spectacular tails of ionized gas in the Virgo cluster galaxy NGC 4569

We obtained using MegaCam at the CFHT a deep narrow band Halpha+[NII] wide field image of NGC 4569, the brightest late-type galaxy in the Virgo cluster. The image reveals the presence of long tails of diffuse ionised gas without any associated stellar component extending from the disc of the galaxy up to ~ 80 kpc (projected distance) with a typical surface brightness of a few 10^-18 erg s-1 cm-2 arcsec-2. These features provide direct evidence that NGC 4569 is undergoing a ram presure stripping event. The image also shows a prominent 8 kpc spur of ionised gas associated to the nucleus that spectroscopic data identify as an outflow. With some assumptions on the 3D distribution of the gas, we use the Halpha surface brightness of these extended low surface brightness features to derive the density and the mass of the gas stripped during the interaction of the galaxy with the ICM. The comparison with ad-hoc chemo-spectrophotometric models of galaxy evolution indicates that the mass of the Halpha emitting gas in the tail is comparable to that of the cold phase stripped from the disc, suggesting that the gas is ionised within the tail during the stripping process. The lack of star forming regions suggests that mechanisms other than photoionisation are responsible for the excitation of the gas (shocks, heat conduction, magneto hydrodynamic waves). This analysis indicates that ram pressure stripping is efficient in massive (M_star ~ 10^10.5 Mo) galaxies located in intermediate mass (~ 10^14 Mo) clusters under formation. It also shows that the mass of gas expelled by the nuclear outflow is ~ 1 % than that removed during the ram pressure stripping event. All together these results indicate that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism responsible for the quenching of the star formation activity of galaxies in high density environments.

Line-defect mediated formation of hole and Mo clusters in monolayer molybdenum disulfide

The production of hole and Mo cluster by electron beam irradiation in molybdenum disulfide (MoS2), which consists of S-Mo-S layers, is monitored over time using atomic resolution transmission electron microscopy. S vacancies are firstly formed due to knocking off of S atoms and then line defects are induced due to accumulation of S vacancies in MoS2 sheet instead of forming a hole. The line defects tend to be merged at a point and a hole is formed subsequently at the point. Mo atoms tend to be clustered discretely as a nano sheet along the edge of the hole due to difference in displacement threshold energy between Mo and S atoms under electron irradiation. After Mo clusters are nearly separated from MoS2 sheet, the clusters are transformed into body-centered cubic nanocrystal of Mo during prolonged electron beam irradiation. The line defect mediated formation of hole and Mo cluster only occurs within a single grain of monolayer MoS2 sheet.

In situ spectroscopic investigations of MoOx/Fe2O3 catalysts for the selective oxidation of methanol

Methoxy adsorbed on MoOx/Fe2O3 surfaces.

Phase Transition Mechanism and Electrochemical Properties of Nanocrystalline MoSe2 as Anode Materials for the High Performance Lithium-Ion Battery

The real application of lithium-ion batteries in electric vehicles lacks the ideal anode materials. Herein, we report both experimental and theoretical study of MoSe2 nanocrystals as the anode materials. MoSe2 nanocrystals are successfully synthesized via a facile thermal-decomposition process. As the anode, the nanocrystalline MoSe2 yields the initial discharge and charge capacities of 782 and 600 mA h g–1 at the current of 0.1 C in a voltage of 0.1–3 V. First-principles simulation demonstrates that, during the initial discharge process, there is a Li atoms induced phase transition from 2H-MoSe2 to the O-MoSe2 phase at 0.9 V, and then Mo cluster occurs as more Li atoms intercalated into the MoSe2 lattice, which is associated with the formation of Mo and Li2Se. And the following charge/discharge processes are related to the conversion reaction between Mo and Li2Se. Meanwhile, the Li ion vacancy-hopping diffusion mechanism from octahedron to tetrahedron in MoSe2 lattice is proposed based on a quasi-2D ener...

Thin films of size-selected Mo clusters: growth modes and structures.

Thin films of MoO3 were prepared by deposition of size-selected ligand-free Mo clusters under high vacuum conditions and subsequent exposure to air. The growth pattern is highly dependent on the cluster size. At low coverage, small clusters (Mo51) form a continuous monolayer of fused particles. On top of this monolayer, additional clusters survive as individual entities. Medium sized clusters (Mo251 and Mo1253) do not coalesce and form a monolayer of clusters. Close examination using in situ scanning tunneling microscopy reveals a local order of the particles. At higher coverage a new pattern of large 3-dimensional aggregations of clusters (pylons) appears. The pylons are not formed under high vacuum conditions. Their formation is most likely caused by the air exposure. For the largest clusters (Mo3349) studied here, no monolayer is formed. Instead, the clusters are randomly distributed as expected for particles with zero mobility. These results demonstrate the high potential of cluster deposition for the production of new types of nanostructured surfaces, thin films and nanomaterials.

'All-Metal' Aromatic Sandwich Molecules: An Electronic Structure and Transport Study.

Electronic structure and transport is theoretically studied for neutral, all-metal aromatic sandwich molecules, Al4MAl4 (M = Cr, Mo) along with Al4 and Al4M (M = Cr, Mo) clusters in two-probe setups with silver and gold electrodes. Detailed electronic structure and transport studies of metallaromatic Al4MAl4 molecules show high electronic conductance [2.5*10(-4) S for Al4CrAl4 and 2.9*10(-4) S for Al4MoAl4] and three conduction channels simultaneously contribute to the total transmission probability. The study of transport properties of the bare Al4 cluster and Al4M cluster also show very high electronic conductance. The neutral Al4 cluster, when connected parallel to the electrodes, four Al atoms couple to the electrode atoms and at least eight electron conduction pathways contribute simultaneously to the conductance whereas for perpendicular connectivity only three conduction channels operate. All the molecules couple strongly to the electrodes by well-defined metal-metal bonds owing to their metallic nature indicating an easier electrode integration process, and the calculated current voltage curves are almost linear till applied voltages of 1 V for Al4MAl4 (M = Cr, Mo). The electronic transport of the clusters studied here resembles the values found for metal atomic chains in break junction studies.

Study of the electronic and the structural properties of small molybdenum clusters via projector augmented wave pseudopotential calculations

We studied the structural and the electronic properties of small Mo clusters (n = 2 ~ 8) via projector augmented wave pseudopotential calculations using plane wave basis functions. Our results show that the 4s- and 4p-semicore states play important roles in the description of small Mo clusters. Also, the dimerization tendency observed in previous theoretical calculations is significantly reduced when the semicore states are explicitly included as the valence states.

Molybdenum-encapsulation modified the optical property of single walled carbon nanotubes

Changes in the optical properties of single walled carbon nanotubes (SWNTs) caused by the encapsulation of molybdenum (Mo) clusters were investigated in the current research. Detailed transmission electron microscope observations showed that the encased Mo clusters within the hollow core of SWNTs exhibited in the form of short rod-like structure, indicating the growth of the clusters within the confined nano space. The upshifted G-band frequency as well as the quenched photoluminescence and absorption signals signified the modulation in the electronic properties of SWNTs caused by a strong coupling interaction between the nanotube and the Mo clusters.

Structural diversity of polyoxomolybdate clusters along the three-fold axis of the molybdenum storage protein

The molybdenum storage protein (MoSto) can store more than 100 Mo or W atoms as discrete polyoxometalate (POM) clusters. Here, we describe the three POM cluster sites along the threefold axis of the protein complex based on four X-ray structures with slightly different polyoxomolybdate compositions between 1.35 and 2Å resolution. In contrast to the Moα-out binding site occupied by an Mo3 cluster, the Moα-in and Moβ binding sites contain rather weak and non-uniform electron density for the Mo atoms (but clearly identifiable by anomalous data), suggesting the presence of POM cluster ensembles and/or degradation products of larger aggregates. The “Moα-in cluster ensemble” was interpreted as an antiprism-like Mo6 species superimposed with an Mo7 pyramide and the “Moβ cluster ensemble” as an Mo13 cluster (present mostly in a degraded form) composed of a pyramidal Mo7 and a Mo3 building block linked by three spatially separated MoOx units. Inside the ball-shaped Mo13 cluster sits an occluded central atom, perhaps a metal ion. POM cluster formation at the Moα-in and Moβ sites appears to be driven by filtering out and binding/protecting self-assembled transient species complementary to the protein template.

Molecular-Scale Transition Metal Oxide Nanocluster Surface-Modified Titanium Dioxide as Solar-Activated Environmental Catalysts

The development of environmental catalysts is an urgent subject to be tackled by scientists and engineers all over the world due to the borderless nature of environmental pollution. We named the catalyst enabling the decomposition of the pollutants by effectively utilizing the solar energy from ultraviolet to infrared as “solar environmental catalysts”. This Feature Article reviews the recent studies on a novel class of solar environmental catalysts consisting of TiO2 and molecular scale oxides of 3d metals and for comparison d10 (Sn) on the surface (MOs/TiO2). The TiO2 surface modification with MO clusters by the chemisorption–calcination cycle (CCC) technique presents novel band engineering for finely tuning the top of the valence band, while the unique physicochemical and electronic properties of MOs/TiO2 give rise to the outstanding photo- and thermocatalytic activities for the decomposition of organic pollutants. In the first part following the Introduction, the CCC technique for forming extremely small MO clusters on TiO2, the structures, physicochemical properties, and electronic structures of MOs/TiO2 are described. The second part deals with their thermo- and photocatalytic activities for the degradation of model organic pollutants and the essential action mechanisms of the MO clusters. The combination of experiments and first-principles density functional theory simulations shows that Co2O3/TiO2 can be a prototype of the solar environmental catalyst with high levels of photo(UV and visible)- and thermocatalytic activities.

Methanolysis of MoCl5 in the presence of different alkaline agents; molecular structures of the polynuclear molybdenum(V) methoxides and electron charge density distribution from X-ray diffraction study of the new K–Mo cluster

The influence of the solution total alkalinity and the base cation and anion types on the structure and properties of molybdenum oxo-methoxides formed in reaction of MoCl5 in methanol as following: MoCl5+CH3OH+M+A−, where M+=K+ or Na+, and A−=OCH3− or OH− was studied. The investigation has shown that hetero-bimetallic oxo-methoxides containing Na or K ions – [NaMo2O2(OCH3)7(CH3OH)] (1), [KMo2O2(OCH3)7(CH3OH)2] (2) – are formed in alkaline media with sodium or potassium methoxides taken as a base. Single crystal X-ray structure determination (XRD) of the complexes 1 and 2 revealed that their crystal structures can be considered as consisting of anionic [Mo2O2(OCH3)7]− and cationic [Na(CH3OH)]+ or [K(CH3OH)2]+ fragments assembled into different supramolecular aggregates. When Na, K or Mg methoxides are used as a base, while the medium remains to be acidic, regardless the cation type the same compounds are formed, namely, [Mo2Cl2(OCH3)8] (3) or [Mo2Cl4(OCH3)6] (4) (in the absence of alkali). When KOH or NaOH are used instead of respective methoxides it has been shown that at weakly acidic (close to neutral) media the octanuclear molybdenum cluster [Mo8O8(μ3-O)4(μ2-O)4(μ3-OCH3)2(μ2-OCH3)4Cl2(CH3OH)4]·6CH3OH (5·6CH3OH) is formed as a main product. The DFT calculations of the mechanism of complex 5 formation were carried out. The process of octanuclear Mo(V) cluster formation from initially formed binuclear ones was shown to be a thermodynamically favorable. The detailed analysis within QTAIM theory of an electron density distribution function ρ(r) in the crystal of 2 obtained directly from its X-ray diffraction data has been performed. This analysis has provided the direct and convincing experimental evidence of the Mo–Mo bond presence in a dimolybdenum clusters and, in addition, allowed to estimate the energy of some important interatomic interactions in 2 and related clusters.

Magnetisation and magnetoresistance of Mo/Fe/Co superlattices

AbstractIn this paper, we present experimental studies of the structure, magnetic behavior and magnetoresistance of magnetic superlattices (MSL) [Mo(12Å)Fe(xÅ)Co(21Å)]*100 (x=4÷43). MSLs have been obtained by cathode sputtering with oscillating electrons on the substrate of mica (muscovite). MSLs investigated at room temperature are soft ferromagnets with induced in‐plane magnetic anisotropy. Changes in the spontaneous magnetization Iso and coercive force Hc, depending on the thickness of Co layers, are of oscillatory behavior, which is apparently because of the interference effects of electron waves in the spacers and interfaces. Stepped shape of the measured hysteresis loops for some MSLs, is apparently determined by the vortex behavior of the clusters magnetic moments, located in the sample plane, that is confirmed by measurements carried out on the scanning probe microscope. The observed high values of Iso, normalized to the content of Fe and Co, exceeding Iso(Fe)=1710 Gs may be observed due to increasing values of spin and orbital magnetic moments of Fe and Co in the cluster formations and in the interfaces in the states of low‐dimensional local atomic environment, as well as the possible formation of ferromagnetic order in Mo clusters. Studies of resistance and magnetoresistance (MR) of the samples at temperatures from 10 K to 290 K show semiconducting behavior of resistance and a positive sign of the magnetoresistance. The maximum value of MR for a sample of [Mo (12A) Fe (16A) Co (21A)] x100 was 0.04% for [Mo (12A) Fe (10A) Co (21A)]x100 ‐ 0.5%. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis, crystal structure and magnetic properties of Li2InMo3O8: A novel reduced molybdenum oxide containing magnetic Mo3 clusters

Powder samples and single crystals of Li2InMo3O8 were obtained by solid state reaction. The structure was determined by single-crystal X-ray diffraction (771 independent reflections for 33 refinable, R1=0.0158 and wR2=0.0354). Li2InMo3O8 is isomorphous with Li2SnMo3O8 and crystallizes in the hexagonal space group P63mc with unit-cell parameters a=5.7931(2)Å, c=10.4681(4)Å and Z=2. The crystal structure consists of distorted hexagonal-close-packed oxygen layers with stacking sequence abac along [001] and that are held together by alternating lithium–indium and molybdenum layers. The Li+ and In3+ ions occupy, respectively, tetrahedral and octahedral sites in the ratio 2:1. The Mo atoms occupy octahedral sites and form strongly bonded triangular clusters involving three MoO6 octahedra that are each shared along two edges, constituting a Mo3O13 unit. The variations of the Mo–Mo and Mo–O bond lengths according to the number of electrons per Mo3 cluster are discussed. The trivalent oxidation state of the indium leads to one unpaired electron per Mo3 and thus gives rise to a paramagnetic spin behavior with an effective magnetic moment of 1.5μB per Mo3 cluster. The magnetic susceptibility vs. temperature curve also shows a maximum at 25K arising probably from an antiferromagnetic ordering between the Mo3 clusters.

A first-principles study of structure, orbital interactions and atomic oxygen and OH adsorption on Mo-, Sc- and Y-doped nickel bimetallic clusters

Abstract Density functional theory (DFT) has been used to study the stability, orbitals interactions and oxygen and hydroxyl chemisorption properties of Ni n M (1 ⩽ n ⩽ 12) clusters. A single atom doped-nickel clusters increase the stability, and icosahedral Ni 12 Mo cluster is the most stable structure. Molybdenum atom prefers to exhibit center at the cluster ( n ⩾ 10) rather than edge, while Sc and Y atom remain at the edge. The Ni–Mo bond lengths are smaller than the Ni–Sc and Ni–Y. The pDOS results show that the d – d orbitals interactions are mainly dominating on the stability of clusters, while p orbitals have a small effect on the stability. The Mo-doped nanoclusters have the highest oxygen and OH chemisorption energy, and the most favorable adsorption site is on the top Mo site. The larger cluster distortion is found for the Sc- and Y-doped structures compared to other clusters. The oxygen 2 p orbitals are strongly hybridizing with the Mo 4 d orbitals ( n p and Ni 3 d , 4 s and Mo 5 s orbitals. The Mo-doped clusters are significantly increased the chemisorption energies that might improve the passive film adherence of nanoalloys.

Self-assembly of two ring-shaped hexanuclear Mo(vi) clusters

Two hexanuclear molybdophosphonates, Na2H4{(CH3COO)[N(CH2PO3)3]Mo6O17(OH)}·13H2O (1) and Na2(NH4)4[Mn2Na2(H2O)2]{[HN(CH2PO3)2](CH3COO)PMo6O22}2·16H2O (2), have been successfully synthesized and characterized by X-ray crystallography, elemental analysis, IR spectra and XRPD, along with a 31P NMR spectroscopic study for 1 and a magnetic susceptibility study for 2. Compounds 1 and 2 are prepared in solution by the self-assembly of the amino trimethylene phosphonic acid (noted as ATMP) ligand and heptamolybdate. Compound 1 exhibits a ring-shaped cluster with two branches of the ligand bound off-center, while the introduction of Mn ions breaks the central P–C bond to form a dinuclear Mn(II) sandwich-type polyanion 2. The magnetic susceptibility of 2 shows strong antiferromagnetic interactions between the two MnII cores.

Synthesis, Crystal and Electronic Structures, and Thermoelectric Properties of the Novel Cluster Compound Ag3In2Mo15Se19

Polycrystalline samples and single crystals of the new compound Ag3In2Mo15Se19 were synthesized by solid-state reaction in a sealed molybdenum crucible at 1300 °C. Its crystal structure (space group R3̅c, a = 9.9755(1) Å, c = 57.2943(9) Å, and Z = 6) was determined from single-crystal X-ray diffraction data and constitutes an Ag-filled variant of the In2Mo15Se19 structure-type containing octahedral Mo6 and bioctahedral Mo9 clusters in a 1:1 ratio. The increase of the cationic charge transfer due to the Ag insertion induces a modification of the Mo–Mo distances within the Mo clusters that is discussed with regard to the electronic structure. Transport properties were measured in a broad temperature range (2–1000 K) to assess the thermoelectric potential of this compound. The transport data indicate an electrical conduction dominated by electrons below 25 K and by holes above this temperature. The metallic character of the transport properties in this material is consistent with electronic band structure calculations carried out using the linear muffin-tin orbital (LMTO) method. The complex unit cell, together with the cagelike structure of this material, results in very low thermal conductivity values (0.9 W m–1 K–1 at 300 K), leading to a maximum estimated thermoelectric figure of merit (ZT) of 0.45 at 1100 K.

Reactive molecular dynamics study of Mo-based alloys under high-pressure, high-temperature conditions

Structural metal alloys are of vital importance for a clean energy economy, but the current trial-and-error alloy development methodology is expensive and time consuming. In this study, we demonstrate the capability of the ReaxFF force field model to predict mechanical properties and provide a fully dynamic description of oxidation and sulfidation of Mo-based alloys under high-pressure, high-temperature conditions using molecular dynamics (MD) method. The advantage of the ReaxFF approach is in its ability to model the formation and breaking of chemical bonds within the quantum framework but several orders of magnitude faster than the traditional density functional theory models. ReaxFF-MD predictions were compared to the literature Mo shock compression measurements at 300 K and 1673 K in the pressure range of 0–350 Pa, and densities and Young’s modulus in the temperature range of 300–1500 K. Analysis of oxidation of Mo and Ni clusters and surface slabs showed that Mo oxidation proceeded at a significantly higher rate than the Ni oxidation and involved oxygen transport inside the metal cluster coupled to large heat release that caused extensive surface melting. The oxidation simulations of Mo3Ni clusters showed high production of Mo oxides and a low concentration of Ni-oxides in the gas phase. This was attributed to the higher chemical stability of Mo-oxide gas phase species. Modeling of H2S interactions with Mo slab demonstrated that sulfur atoms increasingly agglomerated in the surfaces layers of the slab as the simulation proceeded, diffusing deeper into the slab in their atomic forms. A combined ReaxFF Mo/Ni/C/O/N/S/H parameter set enabled us to obtain a detailed atomistic analysis of complex physical and chemical events during the combustion of a complex fuel molecule on a reactor surface.

ChemInform Abstract: Friedel—Crafts‐Type Allylation of Nitrogen‐Containing Aromatic Compounds with Allylic Alcohols Catalyzed by a [Mo3S4Pd(η3‐allyl)] Cluster.

AbstractThe Mo cluster efficiently promotes the reaction of dialkylanilines and indoles with allylic alcohols.

Nature’s Polyoxometalate Chemistry: X-ray Structure of the Mo Storage Protein Loaded with Discrete Polynuclear Mo–O Clusters

Some N(2)-fixing bacteria prolong the functionality of nitrogenase in molybdenum starvation by a special Mo storage protein (MoSto) that can store more than 100 Mo atoms. The presented 1.6 Å X-ray structure of MoSto from Azotobacter vinelandii reveals various discrete polyoxomolybdate clusters, three covalently and three noncovalently bound Mo(8), three Mo(5-7), and one Mo(3) clusters, and several low occupied, so far undefinable clusters, which are embedded in specific pockets inside a locked cage-shaped (αβ)(3) protein complex. The structurally identical Mo(8) clusters (three layers of two, four, and two MoO(n) octahedra) are distinguishable from the [Mo(8)O(26)](4-) cluster formed in acidic solutions by two displaced MoO(n) octahedra implicating three kinetically labile terminal ligands. Stabilization in the covalent Mo(8) cluster is achieved by Mo bonding to Hisα156-N(ε2) and Gluα129-O(ε1). The absence of covalent protein interactions in the noncovalent Mo(8) cluster is compensated by a more extended hydrogen-bond network involving three pronounced histidines. One displaced MoO(n) octahedron might serve as nucleation site for an inhomogeneous Mo(5-7) cluster largely surrounded by bulk solvent. In the Mo(3) cluster located on the 3-fold axis, the three accurately positioned His140-N(ε2) atoms of the α subunits coordinate to the Mo atoms. The formed polyoxomolybdate clusters of MoSto, not detectable in bulk solvent, are the result of an interplay between self- and protein-driven assembly processes that unite inorganic supramolecular and protein chemistry in a host-guest system. Template, nucleation/protection, and catalyst functions of the polypeptide as well as perspectives for designing new clusters are discussed.