A First‐Cycle Coulombic Efficiency Higher than 100 % Observed for a Li2MO3 (M=Mo or Ru) Electrode

The lithiation/de‐lithiation behavior of a ternary oxide (Li₂MO₃, where M=Mo or Ru) is examined. In the first lithiation, the metal oxide (MO₂) component in Li₂MO₃ is lithiated by a conversion reaction to generate nano‐sized metal (M) particles and two equivalents of Li₂O. As a result, one idling Li₂O equivalent is generated from Li₂MO₃. In the de‐lithiation period, three equivalents of Li₂O react with M to generate MO₃. The first‐cycle Coulombic efficiency is theoretically 150 % since the initial Li₂MO₃ takes four Li⁺ ions and four electrons per formula unit, whereas the M component is oxidized to MO₃ by releasing six Li⁺ ions and six electrons. In practice, the first‐cycle Coulombic efficiency is less than 150 % owing to an irreversible charge consumption for electrolyte decomposition. The as‐generated MO₃ is lithiated/de‐lithiated from the second cycle with excellent cycle performance and rate capability.     

Size-Specific Reactivities of Vanadium Oxide Cluster Cations

This article is intended to summarize recent studies on the reactivity and dynamics of gas-phase vanadium oxide cluster cations in terms of their dependence on the size and stoichiometry of the selected clusters. In addition, the effects of coordination, oxidation states of the vanadium atoms, influence of charge, and ionization potentials on the reactivity of these clusters are presented. Reactions of the clusters V₃ O ₇ ⁺ and V₅ O ₁₂ ⁺ with 1-butene, 1,3-butadiene, and difluoromethane differ significantly from those of similar clusters such as V₃ O ₆ ⁺ and V₅ O ₁₁ ⁺ . While oxygen transfer and carbon–carbon cracking reactions are observed for the former clusters, the latter primarily associate the neutral reactant species. These differences are largely related to the oxidation states of the vanadium atoms within the cluster, but also display a dependence on the size of the cluster, with the smaller clusters being more reactive than the larger ones. Reactions with carbon tetrachloride display a dependence on the coordination of the clusters, but also display a distinct change in reaction channels from the chloride transfer reaction for the smaller clusters to the oxidative chloride transfer and formation of neutral phosgene for cluster with more than three vanadium atoms. In contrast, the dehydrohalogenation reactions of CH₃CF₃ display little dependence on the size of the clusters.     

Quantum chemical calculation of the catalytic reaction of ethane dehydrogenation on gallium oxide-hydroxide binuclear clusters in oxidized GaO/ZSM-5 zeolite

The catalytic activity of oxidized GaO/HZSM-5 in the reaction of alkane dehydrogenation can be due to hydrogenated gallium oxide clusters stabilized in the cationic positions of the zeolite. The binuclear gallium oxide clusters [Ga₂O₂]²⁺ in oxidized gallium-substituted high-silica zeolite HZSM-5, which are isomeric to two gallyl ions [GaO]⁺ stabilized on two spatially separated lattice aluminum ions, were considered using the DFT method within the framework of a cluster approach. It was found that, even in the case of a relatively large distance between these aluminum ions, gallium oxide particles in oxidized GaO/HZSM-5 can occur as charged planar [Ga₂O₂]²⁺ four-membered rings. These cluster particles exhibited a high affinity to hydrogen, and they were readily hydrogenated with the retention of their structural integrity. It was demonstrated that this partially hydrogenated cluster could be responsible for the catalytic process of ethane dehydrogenation. In the first step, ethane dissociatively added to the [Ga₂O₂H₂]²⁺ cluster. Then, the ethylene molecule was eliminated from the resulting intermediate to leave the [Ga₂O₂H₄]²⁺ cluster. The cycle was closed by the elimination of a hydrogen molecule with the formation of the initial structure of [Ga₂O₂H₂]²⁺.     

Electrocatalytic Oxidation of Ethylene Glycol at Pt/Nanosized MOx/GC Composite Electrodes: SnO2 in Comparison to CeO2 and WO3

Stable metal oxides insoluble in acidic medium have been prepared and characterized. The influence of the type of metal oxide (MO_x) on the activity of Pt towards ethylene glycol oxidation in acidic medium has been examined. All modified Pt/MO_x/glassy carbon (GC) electrodes exhibited a better activity compared to Pt/GC. While Pt/SnO₂/GC electrode exhibited the highest activity, Pt/CeO₂/GC revealed the best tolerance against poisoning process.     

Catalytic Hydrodehydration of Cyclohexanone,Hydrogenation of 2-Cyclohexen-1-one,and Dehydrogenation of Cyclohexene over a Mo Chloride Cluster with an Octahedral Metal Framework

A silica gel-supported molybdenum halide cluster, (H₃O)₂[(Mo₆Cl₈)Cl₆]·6H₂O (1), developed selective catalytic activity for the condensation of cyclohexanone to cyclohexylbenzene and cyclohex-1-enylbenzene, when it was allowed to react in a stream of helium at 300°C. Halide clusters of Nb, Ta, and W of the same metal framework supported on SiO₂ also catalyzed the condensation at 400°C. However, at 400°C, 1 catalyzed disproportionation, and selectivity increased with increasing temperature, yielding cyclohexene and its dehydrogenation products, 1,3-cyclohexadiene and benzene, and 2-cyclohexen-1-one and its dehydrogenation product, phenol. When the same reaction was performed in a stream of hydrogen above 400°C, hydrodehydration proceeded almost exclusively, producing cyclohexene and its dehydrogenation products. 2-Cyclohexen-1-one was hydrogenated to cyclohexanone under the same reaction conditions utilizing hydrogen molecules, whereas cyclohexene was dehydrogenated via 1,3-cyclohexadiene to benzene. The active site developed on 1 was assumed to be a molybdenum atom, which becomes isoelectronic with the platinum metals by accepting two or more electrons from the ligands.     

Hydrophilic CO2‐based biodegradable polycarbonates: Synthesis and rapid thermo‐responsive behavior

Common CO₂‐based biodegradable polycarbonates like poly(propylene carbonate) or poly(cyclohexene carbonate) are generally hydrophobic, leading to slow biodegradation rate and poor cell adhesion, which limit their applications in the biomedical field. Here hydrophilic polycarbonates were prepared by one‐pot terpolymerization of CO₂, propylene oxide (PO), and 2‐((2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)methyl)oxirane (ME₃MO) using binary Salen Co(III)‐Cl/PPNCl catalyst system. The resultant terpolymers showed one glass transition temperature (T_g), which decreased with the increase of ME₃MO units in the terpolymers (F_ME3MO). Water contact angles of the resultant terpolymers with F_ME3MO of 4.2?23.6% were 68?25°, while that of poly(propylene carbonate) was 90°, indicating that the terpolymers became hydrophlilic. Furthermore, the terpolymers with F_ME3MO more than 25.8% exhibited reversible and rapid thermo‐responsive property in water, and the lower critical solution temperature (LCST) was highly sensitive to F_ME3MO. In particular, aqueous solution of the terpolymer with F_ME3MO of 72.6% showed a LCST around 35.2 °C, close to body temperature, which was promising for biomedical applications, especially for in vivo applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2834–2840.     

The formation and photolysis of tantalum sulfide cluster ions

Tantalum sulfide cluster ions were produced by direct laser ablation, and were studied with a tandem time-of-flight mass spectrometer. The main dissociation channel of the UV-photolysis (248 nm) of tantalum sulfide cluster ions is sequent S₂ loss. Structures with Ta₃S₄ and Ta₄S₆ as frameworks were suggested for the large tantalum sulfide cluster ions.The work was supported by the National Natural Science Fouldation of China.     

Thermal Conversion of Methane to Formaldehyde Promoted by Gold in AuNbO3+ Cluster Cations

In addition to generation of a methyl radical, formation of a formaldehyde molecule was observed in the thermal reaction of methane with AuNbO₃⁺ heteronuclear oxide cluster cations. The clusters were prepared by laser ablation and mass‐selected to react with CH₄ in an ion‐trap reactor under thermal collision conditions. The reaction was studied by mass spectrometry and DFT calculations. The latter indicated that the gold atom promotes formaldehyde formation through transformation of an Au?O bond into an Au?Nb bond during the reaction.     

Size-dependent barriers for reaction of aluminum cluster ions with oxygen

Reactions of cooled, size-selected aluminum cluster ions (Al_n⁺, n = 1–8) with oxygen have been studied at collision energies from 0.15 to 10.0 eV (center-of-mass) under single-collision conditions. With the exception of the atomic ion, all size clusters undergo exoergic reactions which result in extensive fragmentation of the metal cluster framework. Significant energy barriers are found for reaction of all clusters except the dimer. The barrier height increases with cluster size from Al₃⁺ to Al₇⁺, then drops for Al₈⁺.     

Ungewöhnliche reaktion eines 1-cyclopropylvinyl-kations

1-Bromo-1-cyclopropyl-2-methyl-1-propene (7) does not react with cyclohexene and AgSbF₆ with formation of the expected cycloadduct 9. The first generated cyclopropylvinyl-cation 8 rearranges to the allyl-cation 10 which after addition to the olefins cyclohexene and 2,3-dimethyl-2-butene (19) via unusual rearrangements gives the dienes 17 and 20 respectively.     

Hydrogen‐Atom Abstraction from Methane by Stoichiometric Vanadium–Silicon Heteronuclear Oxide Cluster Cations

Vanadium–silicon heteronuclear oxide cluster cations were prepared by laser ablation of a V/Si mixed sample in an O₂ background. Reactions of the heteronuclear oxide cations with methane in a fast‐flow reactor were studied with a time‐of‐flight (TOF) mass spectrometer to detect the cluster distribution before and after the reactions. Hydrogen abstraction reactions were identified over stoichiometric cluster cations [(V₂O₅)_n(SiO₂)_m]⁺ (n=1, m=1–4; n=2, m=1), and the estimated first‐order rate constants for the reactions were close to that of the homonuclear oxide cluster V₄O₁₀⁺ with methane. Density functional calculations were performed to study the structural, bonding, electronic, and reactivity properties of these stoichiometric oxide clusters. Terminal‐oxygen‐centered radicals (O_t ^. ) were found in all of the stable isomers. These O_t ^. radicals are active sites of the clusters in reaction with CH₄. The O_t ^. radicals in [V₂O₅(SiO₂)_1–4]⁺ clusters are bonded with Si rather than V atoms. All the hydrogen abstraction reactions are favorable both thermodynamically and kinetically. This work reveals the unique properties of metal/nonmetal heteronuclear oxide clusters, and may provide new insights into CH₄ activation on silica‐supported vanadium oxide catalysts.     

ZnO and TiO2 clusters as catalyst in the addition and abstraction reaction of acrylic acid with the OH radical

The present work displays the theoretical analysis on the role of metal oxide clusters as an effective catalyst in the reaction between acrylic acid and OH radical, which has an energy barrier of 12.4 kcal/mol. The formation of metal oxide cluster such as ZnO and TiO₂ with varying size from monomer to hexamer is analyzed using cohesive energy, which increases with cluster size. Adsorption of acrylic acid on clusters reveals that dimer ZnO and tetramer TiO₂ are good adsorbed entities. The dimer ZnO and tetramer TiO₂ clusters have reduced the barrier height. However, from the thermodynamical analysis of H-abstraction and OH addition reaction, the dimer ZnO cluster is found to be a good catalyst than a tetramer TiO₂ cluster. The favorable H abstraction and OH addition reactions are feasible at the active methylene group (–CH). OH addition reactions dominate over the H abstraction reaction. Further, the presence of metal oxide clusters enhances the rate of the reaction between acrylic acid and OH radical. The kinetics of the favorable reaction with a dimer ZnO cluster has a rate constant of 7.80 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, which is higher than the literature report (1.75 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹). Overall, ZnO and TiO₂ metal oxide clusters can be effectively utilized as catalyst.     

New Method of Synthesis of β-Haloalkyl Alkynyl Sulfides: Reaction of Alkynesulfenamides with Olefins in the Presence of Phosphoryl Halides

Reactions of alkynelsufenamides with olefins (such as cyclohexene, norbornene, 1-hexene, 1-octene, allylbenzene, and styrene) in the presence of phosphoryl halides (POCl₃, POBr₃) afforded 70–95% of β-halo-substituted alkyl alkynyl sulfides. The reactions with cyclohexene and norbornene are characterized by trans stereoselectivity. Alkynylsulfenylation of terminal alkyl- and benzylacetylenes occurs in a regioselective fashion with predominant formation of the corresponding anti-Markownikoff adducts, while the addition to styrene yields halogen-containing sulfides according to the Markownikoff rule.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 7, 2005, pp. 977–982.Original Russian Text Copyright © 2005 by Beloglazkina, Belova, Dubinina, Garkusha, Buryak, Zyk.     

Synthesis and Isolation of Titanium Metal Cluster Complexes and Ligand-Coated Nanoparticles with a Laser Vaporization Flowtube Reactor

A new laser vaporization flow reactor (LVFR) is described consisting of a laser ablation cluster source combined with a fast flowtube reactor for the production and isolation of ligand-coated metal clusters. The source includes high repetition rate laser vaporization with a 100 Hz KrF (248 nm) excimer laser, while cluster growth and passivation with ligands takes place in a flowtube with ligand addition via a nebulizer spray. Samples are isolated in a low temperature trap and solutions containing the clusters are analyzed with laser desorption time-of-flight mass spectrometry. Initial experiments with this apparatus have trapped Ti _x (ethylenediamine) _y complexes which apparently have linear metal units with octahedral ligand coordination. Other experiments have produced and isolated clusters of the form Ti _x O _y (THF) _z that apparently have linear metal oxide cores and larger (TiO₂) _x (THF) _y nanoparticle species. The isolation of these new cluster species suggest that the LVFR instrument has considerable potential for the production of new nanocluster materials.     

Polymerization and Catalytic Properties of Cluster-Containing Monomers and Polymers

Summary : Cluster-containing monomers were obtained and characterized. Mono- and disubstituted products were obtained under mild conditions via the interaction of Rh₆(CO)₁₆ with 4-vinylpyridine (4-VPy). Substitution of labile acetonitrile ligand in Rh₆(CO)₁₅NCMe by allyldiphenylphosphine (AlPPh₂) yields Rh₆(CO)₁₄(µ,η²-PPh₂CH₂CHCH₂) with formation of π-complex. The copolymerization of cluster-containing monomers synthesized with traditional monomers has been studied. It was found that Rh₆- containing monomers change neither the ligand surroundings nor the structure of cluster monomer framework during polymerization reaction. Polymer-immobilized clusters were found to be active in hydrogenation reactions of cyclohexene.     

Reactions of carbon cluster ions stored in an RF trap

Reactions of carbon clusterions with O₂ were studied by using an RF ion trap in which cluster ions of specific size produced by laser ablation could be stored selectively. Reaction rate constants for positive and negative carbon cluster ions were estimated. In the case of the positive cluster ions, these were consistent with the previous experimental results using FTMS. Negative carbon cluster ions C _n ^– (n=4–8) were much less reactive than positive cluster ions. The C_nO^– products were seen only in n=4 and 6.     

Effects of functional group interactions on the bimolecular and dissociation reactions of diols

The influence of functional group interactions on the bimolecular and dissociation reactions of diols were examined in a quadrupole ion trap mass spectrometer. Reactions of dimethyl ether ions with diols resulted in formation of (M + H)⁺ ions and (M + 13)⁺ ions (by net methyne addition). The product distribution depended on the relative separation of the hydroxyl groups within each diol, with the more proximate diols producing the greatest abundance of (M + 13)⁺ ions compared to (M + H)⁺ ions. The enhancement of the formation of (M + 13)⁺ ions is attributed to the capability for electrostatic interactions between the hydroxyl groups and the electropositive methylene group of the methoxymethylene reagent ion. The enhancement is most significant for diols that can adopt five- or to a lesser extent six-membered ring transition states (i.e, any 1,2 or 1,3 diol). Collision-activated dissociation (CAD) techniques, including both sequential activation experiments (MS ⁿ ) and comparison of CAD spectra for model compounds, suggest that the (M + 13)⁺ ions are protonated cyclic diethers.     

Reactions of indium phosphide cluster cations with ammonia and trimethylamine

Chemistry of indium phosphide clusters is studied using the powerful trapped ion cell techniques of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry in conjunction with an external cluster source and ion guide. The external source is capable of generating a wide range of cluster ions which the ion guide loads with high efficiency into the FTICR cell. The differential pumping of the ion guide allows for operation of the FTICR at requisite low pressure conditions while extracting clusters generated in a high pressure environment. Highly selective reactions of indium phosphide clusters are observed with ammonia and trimethylamine. Of all the In_xP⁺_y cluster sizes and stoichiometries studied, only the indium dimer ion reacts exothermically with ammonia. Thermalized In⁺₂ reacts by indium ion transfer to ammonia. Owing to its much higher basicity, trimethylamine is much more reactive. The smaller indium phosphide clusters react by indium ion transfer to trimethylamine. As the clusters become larger, however, the reaction probability decreases to zero.     

Experimental and theoretical study on the reactivity of phosphorus-containing cubane type clusters [RMPR’]<Subscript>4</Subscript> (M = Ga,In) toward pyridine

Reactions of cubane type clusters [EtGaPSi(Me)₂Thex]₄ [Thex = CMe₂(Pr-i)] and {EtInP[Si(i-Bu)₃]}₄ with pyridine were studied. The temperature dependences of vapor pressure over individual solid compounds were measured using a membrane pressure gauge. At a temperature above 200°C the examined clusters undergo irreversible thermal decomposition due to instability of organic substituents. According to the experimental data, the cubane clusters do not react with gaseous pyridine below their decomposition temperature. Thermodynamic parameters for the isomerization of model clusters [HMPH]₄ (M = Ga, In) and their gas-phase reactions with pyridine were calculated by quantum-chemical methods. The addition of pyridine is thermodynamically allowed only at low temperatures.     

Comparison of collision‐ versus electron‐induced dissociation of sodium chloride cluster cations

The collision‐induced dissociation (CID) and electron‐induced dissociation (EID) spectra of the [(NaCl)_m(Na)_n]ⁿ⁺ clusters of sodium chloride have been examined in a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer. For singly charged cluster ions (n = 1), mass spectra for CID and EID of the precursor exhibit clear differences, which become more pronounced for the larger cluster ions. Whereas CID yields fewer product ions, EID produces all possible [(NaCl)_xNa]⁺ product ions. In the case of doubly charged cluster ions, EID again leads to a larger variety of product ions. In addition, doubly charged product ions have been observed due to loss of neutral NaCl unit(s). For example, EID of [(NaCl)₁₁(Na)₂]²⁺ leads to formation of [(NaCl)₁₀(Na)₂]²⁺, which appears to be the smallest doubly charged cluster of sodium chloride observed experimentally to date. The most abundant product ions in EID spectra are predominantly magic number cluster ions. Finally, [(NaCl)_m(Na)₂]^{+ .} radical cations, formed via capture of low‐energy electrons, fragment via the loss of [(NaCl)_n(Na)] ^. radical neutrals. Copyright © 2008 John Wiley & Sons, Ltd.