Unusual selectivity in photooxygenation of alkanes by air in CH3CN solutions catalyzed by CrCl3?C6H5CH2N(C2H5)3Cl

A new system CrCl₃–C₆H₅CH₂N(C₂H₅)₃Cl–CH₃CN for photooxygenation of alkanes is suggested. Unlike metal chlorides and oxocomplexes, it oxidizes alkanes to produce ketones and small amounts of alcohol. Adding of benzene, methylene chloride or ethanol to the cyclohexane solution rises the oxygenation rate and changes the ketone/alcohol ratio. With small amounts of hydroquinone the formation rate of cyclohexanone (but not of cyclohexanol) sharply decreases. Kinetic isotope effect in the oxidation of C₆H₁₂ and C₆D₁₂ is 1 for cyclohexanol and 2.9 for cyclohexanone. Cyclohexanol formation is assumed to follow a mechanism that does not involve free radicals. Free radicals can participate in the route toward ketone.

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CrCl₃–C₆H₅CH₂N(C₂H₅)₃Cl–CH₃CN . , . , /. ( ) . C₆H₁₂ C₆D₁₂ 1 2,9 . , , . , .

     

H2 Dissociation by Au1-Doped Closed-Shell Titanium Oxide Cluster Anions?

Dissociation of molecular hydrogen (H₂) is extensively studied to understand the mechanism of hydrogenation reactions. In this study, H₂ dissociation by Au₁-doped closed-shell titanium oxide cluster anions AuTi₃O₇^- and AuTi₃O₈^- has been identified by mass spectrometry and quantum chemistry calculations. The clusters were generated by laser ablation and massselected to react with H₂ in an ion trap reactor. In the reaction of AuTi₃O₈^- with H₂, the ion pair Au⁺-O₂^2- rather than Au⁺-O^2- is the active site to promote H₂ dissociation. This finding is in contrast with the previous result that the lattice oxygen is usually the reactive oxygen species in H₂ dissociation. The higher reactivity of the peroxide species is further supported by frontier molecular orbital analysis. This study provides new insights into gold catalysis involving H₂ activation and dissociation.     

Lithium insertion into In2S3 studied by perturbed γ-γ angular correlation

Li_xIn₂S₃ was electrochemically prepared with different small amounts x of lithium (0?x?0.13) in order to maintain the initial crystallographic structure of the thiospinel In₂S₃. About 10¹² radioactive ¹¹¹In ions have been implanted into these samples at 400 keV to perform PAC experiments in the temperature range from 10 to 773 K. The results are compared to previous experiments with undoped In₂S₃ samples. According to the structure of In₂S₃ in the β-phase, which belongs to the I4₁/amd space group having a unit cell with 32 In and 48 S atoms and the cell parameters α=7.61 Å and c=32.28 Å, three different electric field gradients were observed. Within two different temperature ranges dynamical EFGs occur, which are clearly influenced by the insertion of Lithium. The strong dependence of one EFG on the Li concentration x can be correlated to the effective charge of the In ions. This correlation is discussed with respect to XRD analyses of the Li_xIn₂S₃ samples and to XANES measurements on a similar sample.     

Phase transition induced by lithium insertion in αI- and αII-VOPO4

Lithium insertion in α_I-VOPO₄ and α_II-VOPO₄, either by chemical or electrochemical route, leads to the same new compound: α_I-LiVOPO₄ (space group P4/nmm). The structure, resolved by neutron and synchrotron diffraction, is made up of planes of corner-connected PO₄ and VO₅ polyhedra, whereas lithium atoms are located between the layers. The reversal of the short vanadyl bond that corresponds to the insertion-induced α_II-α_I transition finds an explanation in terms of lattice energy. It favors the migration of lithium ions in the (0 0 1) interlayer planes, a key parameter for the electrochemical performance as electrode material in Li-ion batteries.     

Electrochemical urea synthesis by co-reduction of CO2 and nitrate with FeⅡ-FeⅢOOH@BiVO4 heterostructures

Traditional urea synthesis under harsh conditions is usually associated with high energy input and has aroused severe environmental concerns.Electrocatalytic C-N coupling by converting nitrate and CO₂ into urea under ambient conditions represents a promising alternative process.But it was still limited by the strong competition between nitrate electrochemical reduction(NO₃ER) and CO₂ electrochemical reduction(CO₂ER).Here,Fe^Ⅱ-Fe^ⅢOO...     

Three-dimensional Co2V2O7·nH2O superstructures assembled by nanosheets for electrochemical energy storage

Hierarchical superstructures assembled by nanosheets can effectively prevent aggregation of nanosheets and improve performance in energy storage. Therefore, we proposed a facile hydrothermal method to obtain three-dimensional（3D） superstructure assembled by nanosheets. We found that the ratio of Co²⁺/HMTA affected the morphology of the samples, and the 3D hierarchical structures of are obtained while the ratio of Co²⁺/HMTA is 12:25. The hierarchical structures with sufficie...     

Deposition of NiO onto MoO3/γ-Al2O3 extrudates by slurry impregnation method

NiO-MoO₃/γ-Al₂O₃ catalysts were prepared by the reaction of γ-Al₂O₃ extrudates with an aqueous slurry of MoO₃, followed by the reaction of the MoO₃/γ-Al₂O₃ catalyst with an aqueous slurry of NiO, Ni(OH)₂, NiCO₃·2Ni(OH)₂·xH₂O, or 2NiCO₃·3Ni(OH)₂·4H₂O and by subsequent drying. The NiO deposition was examined with electron probe microanalysis. The deposited Ni efficiently increased the activity in benzothiophene hydrodesulfurization.     

Synthesis of Silica@α-Fe2O3 nanospheres by surface-initiated ATRP

We reported a new method to prepare Silica@α-Fe₂O₃ nanospheres by surface-initiated atom transfer radical polymerization (ATRP). Firstly, polymerizable surfactants-modified α-Fe₂O₃ nanoparticles were prepared in water-toluene microemulsion. Then, as-synthesized α-Fe₂O₃ nanoparticles acted as the macro-monomer of surface-initiated ATRP on silica nanospheres to make target product. Morphological characterization of the product was performed using transmission electron microscopy (TEM). Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance UV-vis spectroscopy were used to verify the incorporation of α-Fe₂O₃ nanoparticles on silica nanosphere.     

Kinetic study of the oxidation of L-threonine by MnO4? ions

A self-catalytic effect attributed to Mn²⁺ ions was observed when studying the oxidation of L-threonine by permanganate ions. The process obeys the rate equation:

Conductivity and chemical stability of SrCe0.92Nb0.03Tm0.05O3-δ membrane prepared by modified sol-gel method

SrCe0.92 Nb 0.03 Tm0.05 O 3-δ powders were synthesized by a modified sol-gel method using citrate as a chelating agent.X-ray diffraction(XRD) analysis verified SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ powders and membranes consisting of a single perovskite phase.The morphologies of the sintered membranes were investigated by using scanning electron microscopy(SEM) technique.Stability tests demonstrated that the Nb introduction into doped strontium cerate greatly enhanced the chemical stability.Electrical conductivities of SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ and SrCe 0.95 Tm 0.05 O 3-δ were measured by the four-point DC method under 10% H 2 /He atmosphere and temperatures(700-900℃).With a maximum conductivity of 0.0067 S cm-1 at 900℃,the total electrical conductivity of SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ increases with increasing temperature.The H 2 permeation flux of SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ is 0.035 mL cm-2 min-1 when 40% H 2 /He and Ar were used respectively as the feed and sweeping gases at 900℃.     

Pressure-induced transformations in α- and β-Ge3N4: in situ studies by synchrotron X-ray diffraction

Metastable high-pressure transformations in germanium nitride (α- and β-Ge₃N₄ polymorphs) have been studied by energy- and angle-dispersive synchrotron X-ray diffraction at high pressures in a diamond anvil cell. Between P=22 and 25 GPa, the phenacite-structured β-Ge₃N₄ phase (P6₃/m) undergoes a 7% reduction in unit-cell volume. The densification is primarily concerned with the a-axis parameter, in a plane normal to the hexagonal c-axis. Based on results of previous LDA calculations and Raman spectroscopic studies, we propose that the structural collapse is due to transformation into a new metastable polymorph (δ-Ge₃N₄) that has a unit-cell symmetry based upon P3, that is related to the low-pressure β-Ge₃N₄ phase by concerted displacements of N atoms away from special symmetry sites in the plane normal to the c-axis. No such transformation occurs for α-Ge₃N₄, due to the different stacking of linked GeN₄ layers. All three polymorphs (α-, β- and δ-Ge₃N₄) are based on tetrahedrally coordinated Ge atoms, unlike the spinel-structured γ-Ge₃N₄ phase, that contains octahedrally coordinated Ge⁴⁺. Experimentally determined bulk modulus values for α-Ge₃N₄ (K₀=165(10) GPa, K₀′=3.7(4)) and β-Ge₃N₄ (K₀=185(7) GPa, K₀′=4.4(5)) are in excellent agreement with theoretical predictions. The bulk modulus for the new δ-Ge₃N₄ polymorph is only determined above the β-δ transition pressure (P=24 GPa); K=161(20) GPa, assuming K′=4. Above 45 GPa, both α- and δ-Ge₃N₄ polymorphs become amorphous, as determined by X-ray diffraction and Raman scattering.     

Reduction of an amorphous NiO?Al2O3/SiO2 catalyst by different olefins and hydrogen

By static magnetic measurements it was found that the ability to reduction of an amorphous NiO–Al₂O₃/SiO₂ catalyst decreases in the order: but-2-eneshydrogen isobutene>but-1-ene>propeneethene. The reduction temperatures are significantly higher than the dimerization reaction temperatures.

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, NiO–Al₂O₃/SiO₂ : -2>-1> . .

     

Synthesis of γ-butyrolactones containing α,α-difluoromethylenyl bisphosphonate initiated by Na2S2O4

Diethyl iododifluoromethylphosphonate (1) reacted with 4-pentenoic acids in the presence of Na₂S₂O₄ in aqueous acetonitrile solution at ambient temperature to afford various γ-butyrolactones containing α,α-difluoromethylenyl bisphosphonate moiety in moderate to good yields.     

Methanol Synthesis by co2 Hydrogenation over Titanium Modified γ -al2o3 Supported Copper Catalysts

A titanium-modified . -Al₂ O₃ supported copper catalyst has been prepared and used for methanol synthesis by CO₂ hydrogenation. The addition of Ti to the CuO/. -Al₂ O₃ catalyst enhances the activity in CO₂ hydrogenation greatly and makes the copper in the catalyst exist in much smaller crystallites. The effect of contact time on the relative selectivity ( 6 CH₃OH /SCO ) and selectivity of methanol was also investigated. The results indicated that methanol was formed directly from the hydrogenation of CO₂ .     

Super-exchange and Exchange-Enhanced Reactivity in Fe4S4-Mediated Activation of SAM by Radical SAM Enzymes?

[4Fe-4S]-dependent radical S-adenosylmethionine (SAM) proteins are a superfamily of oxidoreductases that can catalyze a series of challenging transformations using the common 5-dAdo radical intermediate. Although the structures and functions of radical SAM enzymes have been extensively studied, the electronic state-dependent reactions of the [4Fe-4S] clusters in these enzymes are still elusive. Herein we performed QM/MM calculations to elucidate the electronic state-dependent reactivity of the [4Fe-4S] cluster in pyruvate-formate lyase activating enzyme. Our calculations show that the electronic state-dependent SAM activation by the [4Fe-4S] clusters in radical SAM enzyme is determined by both the super-exchange and exchange-enhanced reactivities. The super-exchange coupling in the [4Fe-4S] cluster favors the antiferromagnetic coupling between two neighbouring pairs, which results in the \begin{document}$\alpha$\end{document}-electron rather than the \begin{document}$\beta$\end{document}-electron donation from the [4Fe-4S]\begin{document}$^{1+}$\end{document} cluster toward the SAM activation. Meanwhile, in the most favorable electronic state for the reductive cleavage of S\begin{document}$-$\end{document}C5\begin{document}$'$\end{document}, Fe4 would donate its \begin{document}$\alpha$\end{document}-electron to gain the maximum exchange interactions in the Fe4-block. Such super-exchange and exchange-enhanced reactivity could be the general principles for reactivities of [4Fe-4S] cluster in RS enzymes.     

Crystal structure analysis of β-tricalcium phosphate Ca3(PO4)2 by neutron powder diffraction

The crystal structure of sintered β-tricalcium phosphate, Ca₃(PO₄)₂, was refined using a high-resolution neutron powder diffraction data and the Rietveld method. This material was confirmed to have a rhombohedral structure (space group R3c, Z=21). Unit-cell parameters with higher precision (a=b=10.4352(2) Å, c=37.4029(5) Å, α=β=90°, and γ=120° in the hexagonal setting) and positional parameters for oxygen with equal precision were obtained by the neutron powder diffraction technique, compared with the single-crystal X-ray diffraction data by Dickens et al. (J. Solid State Chem. 10 (1974) 232). The site Ca(4) with atomic coordinates [0.0, 0.0, −0.0851(6)] was confirmed to be very different from the other four Ca sites: The position Ca(4) is three-fold coordinated with oxygen atoms, and has lower occupancy factor of 0.43(4), and a higher isotropic thermal parameter. On the contrary, each of the Ca(1), Ca(2), Ca(3), and Ca(5) is fully occupied by one Ca atom and these positions are coordinated with seven, eight, eight, and six oxygen atoms, respectively. The bond valence sums of Ca(4) and Ca(5) are lower (0.7) and higher (2.7), respectively, than the others (1.8-2.1).     

Activity of γ-Al2O3 modified by NaOH in disproportionation of methanethiol

Na⁺/Al₂O₃ catalysts in disproportionation of methanethiol are highly selective towards dimethyl sulfide but less active compared to -Al₂O₃. Their activity falls with increasing Na⁺ in the sample. This decrease is due to the neutralization of Brönsted acid centers on the catalyst.

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Na⁺/Al₂O₃ , , -Al₂O₃. Na⁺ . .

     

Sr2/3Y1/3CoO8/3+δ: Transition from insulating antiferromagnet to metallic ferromagnet by control of the oxygen content

Magnetic and electronic properties of the oxygen deficient ordered perovskite, Sr_2/3Y_1/3CoO_8/3+δ, have been studied for two different oxygen contents corresponding to δ=0.00 and 0.04 in the chemical formula. For the former, at low temperature, the background state is antiferromagnetic insulating as expected from the presence of trivalent cobalt in the high spin-state. Remarkably, the more oxidized compound with a cobalt oxidation state of ≈3.08 is a ferromagnetic half-metal with Consistently, upon application of an external magnetic field, the spin-scattering reduction in the T_C vicinity is responsible for a weak negative magnetoresistance. These dramatic changes of the physical properties for such a slight increase of the cobalt oxidation state are interpreted as a result of the structural disordering created by the extra oxygens. The thermoelectric power measurements, showing a sign change of the Seebeck coefficient as the oxygen content increases, indicate that electrons moving in a metallic e_g band dominate the transport properties of the ferromagnetic and metallic compound. This suggests the existence of an orbital ordering in the pristine compound, related to an ordered array of CoO₄ tetrahedra, which can be collapsed by the presence of these extra oxygen anions.     

α-Phenylselenenylation of aldehydes and ketones with diphenyl diselenide mediated by KF/Al2O3

The utility of KF/Al₂O₃ for the synthesis of α-phenylseleno aldehydes and ketones from the corresponding aldehydes or ketones and diphenyl diselenide has been investigated. Simple stirring of a mixture of aldehyde or ketone and diphenyl diselenide in the presence of KF/Al₂O₃ at room temperature selectively produces the corresponding α-phenylseleno aldehyde or ketone in good to excellent yields.     

Hydrogen peroxide disproportionation by the [TPA2Mn2(μ-Cl)2] complex

The dichloride-bridged [TPA₂Mn₂(μ-Cl)₂]²⁺ complex (I) was synthesized as a structural and functional model complex of the chloride-inhibited manganese catalase, and its catalytic properties in MeCN have been studied. Complex I shows sigmoidal kinetics and the activity is significantly inhibited in the presence of water. The kinetic parameters of the hydrogen peroxide disproportionation by complex I have been successfully fitted with non-Michaelis–Menten kinetics of Hill’s equation, which implies a multiple-step substrate activation of complex I. After termination of the catalysis, the mononuclear [TPA₂Mn](ClO₄)₂ was isolated from the solution. During the catalysis, a new penta-coordinate [TPAMnCl](ClO₄) complex (IV), tending to accumulate at a lower ratio of H₂O₂, was isolated and its X-ray crystallographic structure, as well as physical properties, was determined. Transformation of complex I in the presence of different molar ratios of H₂O₂ was studied by UV–Vis, EPR and ESI-MS spectroscopy. Upon addition of H₂O₂, the catalytic solution turned dark green, with instant evolution of oxygen gas, and the electronic spectra obtained were identical to that of the dark green dioxo bridged [TPA₂Mn₂(μ-O)₂](ClO₄)₃ complex (III). When the catalytic solution was subjected to EPR measurement, the transient peaks corresponding to the electronically localized Mn(II) species developed in a short time at lower concentrations of H₂O₂. The signal was more distinctive in the presence of water, and the complex I·H₂O₂ adduct was suggested as the intermediate species based on ESI-MS measurements. The EPR signal corresponding to complex III was detected at higher concentrations (>800 equiv.) of H₂O₂. As possible catalytic intermediates, the [TPA₂Mn^III₂(μ-O)₂]²⁺ and [TPA₂Mn^III₂(μ-O)(μ-OH)]⁺ species were suggested. A possible catalytic mechanism of H₂O₂ disproportionation by complex I, including the formation of active species and termination of the catalysis, has also been suggested.