Rearrangement Of Oxygen Atoms Research Articles

Constructing Ni-Pt Bimetallic Catalysts for Catalytic Hydrogenation and Rearrangement of Furfural into Cyclopentanone with Insight in H/D Exchange by D2O Labeling.

Developing a metallic catalyst for converting furfural (FAL) to highly valuable products such as cyclopentanone (CPO) is important for fine chemical synthesis by the efficient utilization of biomass resources. The presence of diverse unsaturated carbon atoms in FAL and the rearrangement of oxygen atoms hinder the production of CPO. We developed an optimal nickel (Ni)-to-platinum (Pt) molar ratio (1:0.007) for a bimetallic Ni-Pt/alumina (Al2O3) catalyst with a low Pt loading via an impregnation method to efficiently catalyze the selective hydrogenation of FAL in an aqueous solution to form CPO. The comprehensive characterizations by X-ray diffraction and X-ray absorption near edge structure analyses elucidated the formation of Ni0/Pt0 and Ni2+/Pt4+ after reduction by H2. The addition of a low amount of the Pt-Ni/Al2O3 catalyst resulted in an alleviation of H2 reduction behavior detected by hydrogen temperature-programmed reduction, accompanied by low H2 desorption ability observed by hydrogen temperature-programmed desorption. The catalytic activity of Ni-Pt/Al2O3 was higher than those of Ni/Al2O3 and Pt/Al2O3 catalysts. The maximum CPO yield was 66% with 93% FAL conversion under the optimized conditions (160 °C, 20 bar of H2 pressure, and 2 h). Isotopic deuterium oxide (D2O) labeling revealed the transfer of deuterium (D) atoms from D2O to the intermediates and products during hydrogenation and rearrangement, which confirmed that water was a medium for rearrangement and the source of hydrogen for the reaction. This study developed an efficient catalyst for the catalytic hydrogenation and ring rearrangement of FAL into CPO.

Ultra‐High Capacity and Cyclability of β‐phase Ca0.14V2O5as a Promising Cathode in Calcium‐Ion Batteries

AbstractCrystalline water‐free β‐phase Ca0.14V2O5is reported for the first time as a viable cathode material for calcium‐ion batteries (CIBs). In contrast to layered α‐V2O5and δ‐CaxV2O5·nH2O, which have limited capacity, the β‐phase delivers a reversible capacity of ≈247 mAh g−1, which corresponds to the insertion/extraction of Ca2+between Ca0.14V2O5and Ca1.0V2O5. The process of Ca2+insertion process and the accompanying structural relaxation are theoretically and experimentally verified. The initial insertion of Ca2+into Ca0.14V2O5causes a slight shift of oxygen atoms surrounding hepta‐coordination sites, creating penta‐coordinated sites that are then partially filled up to Ca0.33V2O5. Further insertion occurs through the stepwise occupation of up to 50% of neighboring hexa‐ and tetra‐coordination sites to form Ca0.67V2O5and Ca1.0V2O5, respectively. The rearrangement of oxygen atoms in Ca0.14V2O5also minimizes dimensional changes, leading to high cyclic stability during repeated charge/discharge cycles. The remarkable electrochemical performance of full cells containing a Ca0.14V2O5cathode and a K metal anode in Ca2+/K+hybrid electrolytes, is also demonstrated, thanks to the inertness of K+insertion into Ca0.14V2O5and the absence of calcium plating/stripping. The cyclic stability and high capacity of Ca0.14V2O5is not compromised in hybrid electrolytes, making it a viable CIB cathode.

Selectivity catalytic transfer hydrogenation of biomass-based furfural to cyclopentanone

Because of furfural’s diverse unsaturated groups and the rearrangement of oxygen atoms, the production of cyclopentanone (CPO) from furfural (FF) can be challenging. Herein, a novel nitrogen-doped encapsulated catalyst (Co@NC) was synthesized to catalyze the selective hydrogenation of FF in an aqueous phase to CPO. A CPO yield of 86.5 % was obtained at 200 °C and 3 MPa H2. Meanwhile, furfuryl alcohol (FA) was inferred to be the primary intermediate in the formation of CPO and cyclopentanol (CPL). CPL originated from the further hydrogenation of CPO that was produced via FF selective hydrogenation to FA, followed by FA hydrodeoxgenation to CPO. The main presence of CPO illustrated that it avoided overhydrogenation, which contributed to the tailored hydrogenation ability of Co@NC and facilitated the selective preservation of CO bonds. The N atoms acting as electronegative heteroatoms can not only enhance the adsorption of FF but also provide weak Lewis acid sites for CPO production.

Chemically induced symmetry breaking in the crystal structure of guanidinium uranyl sulfate

The novel uranyl sulfate templated by protonated guanidinium molecules was obtained from aqueous solution under ambient conditions. Its crystal structure was determined by the single crystal X-ray diffraction analysis and evaluated using a topological approach and information-based complexity calculations. The Se-for-S substitution resulted in a symmetry breaking (from orthorhombic in sulfate to monoclinic in selenate) due to the rearrangement of oxygen atoms, so the resulting symmetry is a consequence of interplay between the template-substructure interactions and size of the tetrahedral cation.

Proton leakage across lipid bilayers: Oxygen atoms of phospholipid ester linkers align water molecules into transmembrane water wires

Up to half of the cellular energy gets lost owing to membrane proton leakage. The permeability of lipid bilayers to protons is by several orders of magnitude higher than to other cations, which implies efficient proton-specific passages. The nature of these passages remains obscure. By combining experimental measurements of proton flow across phosphatidylcholine vesicles, steered molecular dynamics (MD) simulations of phosphatidylcholine bilayers and kinetic modelling, we have analyzed whether protons could pass between opposite phospholipid molecules when they sporadically converge. The MD simulations showed that each time, when the phosphorus atoms of the two phosphatidylcholine molecules got closer than 1.6 nm, the eight oxygen atoms of their ester linkages could form a transmembrane ‘oxygen passage’ along which several water molecules aligned into a water wire. Proton permeability along such water wires would be limited by rearrangement of oxygen atoms, which could explain the experimentally shown independence of the proton permeability of pH, H2O/D2O substitution, and membrane dipole potential. We suggest that protons can cross lipid bilayers by moving along short, self-sustaining water wires supported by oxygen atoms of lipid ester linkages.

Pd(110) surface oxide structures investigated by STM and DFT

The adsorption of oxygen on a Pd(1 1 0) surface has been studied with scanning tunneling microscopy (STM). The particular emphasis was given to the preparation of low oxygen coverages with the well known c(2 × 4)-O oxygen phase as a starting structure in the experiments. The oxygen content, surface morphology and structure were changed by annealing the sample to temperatures below the onset of oxygen desorption. The surface was characterized after cool-down to room temperature or temperatures in the range 100–140 K. At low temperatures we found a new oxygen adsorption structure characterized by a (3 × 2) periodicity. We also calculate the O/Pd(1 1 0) surface phase diagram by first-principles thermodynamics. For small coverages, near the low-coverage end of the large stability region of the c(2 × 4)-O structure it was found that a (2 × 3)-deep-O and a (2 × 3)-1D-O structures, which are degenerate in energy, are most stable. Conversely, at high chemical potentials, i.e. high coverages, a (7 × √3)-O structure becomes more stable. The formation of the metastable (3 × 2)-O phase is explained in terms of partial deoxidation via the interaction with residual hydrogen and by quenching of other types of restructuring at low temperatures since the (3 × 2)-O phase can be derived from the c(2 × 4)-O phase by slight rearrangement of oxygen atoms after the oxygen content was lowered from 1/2 to 1/3 of a monolayer. This is not the case with more stable structures of the same coverage which require an additional rearrangement of palladium atoms.

Effects of Sr-doping on the phase transition and electrical properties in PrBa2−xSrxCu3Oy

Effects of Sr-doping on PrBa2Cu3Oy have been investigated in particular reference to the relationship between a phase transition and electrical properties. The orthorhombic to tetragonal (O–T) phase transition has been found to occur at a certain concentration (x) of dopant Sr when the synthesized compound PrBa2−xSrxCu3Oy is annealed in air- or oxygen-atmosphere. However, this transition does not occur for samples annealed in Ar-atmosphere. The resistivity ρ has been found to sharply rise together with occurrence of the O–T transition. This sharp rise in ρ has been first observed in the present work. In contrast, ρ of samples annealed in Ar-atmosphere behaves only as a decreasing function of x, exhibiting no sharp rise. The magnetization has also been found to behave differently according to the annealing process. The O–T transition is described in terms of Pr-incorporation into Ba site and rearrangement of oxygen atoms. The relationship between the crystalline transition and behavior of ρ is described in terms of a percolation process.

Transmission Electron Microscopy Study of Polymorphism in Barium Gallate BaGa2O4

Polymorphism in barium gallate BaGa2O4 was studied using electron diffraction and high resolution electron microscopy. Three modifications of BaGa2O4 with structures closely related to the high-temperature α-form were observed. The phase transitions from γ-BaGa2O4 (a γ = 18.6143(2) Å = 2<formula><radical><radicand>3</radicand></radical></formula>a α, c γ = 8.6544(1) Å = c α, S.G. P63) to β-BaGa2O4 (a β = 2a α, c β = c α S.G. P63) and to the new δ-polymorph having a monoclinic structure (a δ = c α, b δ = 2a α + b α, c δ = 2b α and β ≈ 92°, S.G. P21/c) were induced by electron beam irradiation. High resolution electron microscopy (HREM) observations allow to establish the close similarity between the structures of δ-BaGa2O4 and β-SrGa2O4. The γ→β and β→δ transitions involve a rearrangement of oxygen atoms in the BaO layers together with a tilting distortion of the tetrahedral framework. The microstructure of the δ-phase is characterised by the presence of numerous translation and orientation domains.

Elastic interaction of oxygen atoms on a graphite surface

The elastic interaction energy between two oxygen atoms deposited on a graphite basal plane is calculated by atomic ab initio simulations and continuum theory of elasticity. The comparison between the results obtained with the two different methods, despite their usual length scale domain of application, is very good; attractive and repulsive behaviors are found. We speculate that this type of interaction could play an important role in the rearrangement of oxygen atoms experimentally observed after a weak oxidation of a graphite surface.

Heat capacity of (Hf 1− yAl y)O 0.17 at high temperature

Heat capacities of (Hf 1− y Al y )O 0.17 ( y=0–0.03) were measured from 325 to 905 K by using an adiabatic scanning calorimeter. A heat capacity anomaly was observed around 700 K for all (Hf 1− y Al y )O 0.17 samples and assigned to an order–disorder rearrangement of oxygen atoms. The experimental transition temperatures, the enthalpy change and entropy changes due to the order–disorder transition decreased with increasing aluminium contents. The experimental entropy changes of the order–disorder transition are compared with the theoretical values from the view point of statistical thermodynamics and are discussed.

Thermodynamic Stability of Chemically Delithiated Li ( LixMn2 − x ) O 4

Stoichiometric and excess‐lithium spinels, (x = 0.0, 0.1, 0.2), were treated with diluted . The resulting products retained the spinel structure at reduced lithium content; those with lowest lithium content underwent exothermic phase transitions, observed as peaks in differential scanning calorimetry (DSC) curves between 250 and 300 °C at heating rates of 10 °C/m. The phase transition of the delithiated stoichiometric spinel was followed by powder X‐ray diffraction of heat‐treated samples. The structural analysis shows that the oxygen atoms rearrange first (from cubic to hexagonal packing), leaving the manganese atoms in disordered positions. It is this rearrangement of oxygen atoms that releases most of the heat observed in DSC measurements. Eventually the manganese atoms took their expected positions in the rutile or β‐form of . The metastability of the delithiated compounds turned out not to be the origin of the capacity fade in electrochemical cells using stoichiometric spinel as the cathode.

Effect of Sr and Sr-Ca substitution on the superconductivity of (Er0.76Ca0.24)Ba2(Cu2.76Co0.24)Oz

The structural and superconducting properties of (Er1-xCax)Ba2-ySry(Cu2.76Co0.24)Oz are investigated using X-ray diffraction, resistivity, ac susceptibility, and oxygen content measurements. Increasing the Sr content in (Er0.76Ca0.24)Ba2-ySry(Cu2.76Co0.24)Oz lowers the oxygen content and decreases theT c, which is attributed to the rearrangement of oxygen atoms in the basal plane. This suppression ofT c aty =0.6 cannot be improved by appropriate hole doping with Ca in (Er1-xCax)Ba1.4Sr0.6(Cu2.76Co0.24)Oz forx = 0.24-0.48.

‘Stable to unstable’ transition in the (Cs, O) activation layer on GaAs (100) surfaces with negative electron affinity in extremely high vacuum

The degradation of GaAs photocathodes with negative electron affinity, activated by (Cs, O) and (Cs, F) layers, was studied in a vacuum setup with a basic pressure below 10 −12 mbar. Activation and degradation are similar for (Cs, O) and (Cs, F) activation. A new type of degradation was observed during the operation of a (Cs, O)-activated cathode, showing up as an instability after exposure to oxygen and subsequent reactivation with Cs. The same amounts of oxygen and Cs added to a (Cs, F)-activated surface did not influence its stability. A rearrangement of oxygen atoms in the activation layer is suggested as an explanation of these observations.

Low-frequency internal friction near the antiferromagnetic phase transition in YBa2Cu3O7_8

The temperature spectra of low-frequency internal friction and shear modulus of YBa2Cu3O7-8 ceramics with δ = 0.3-0.8 have been measured. The investigations have shown a number of anomalous features which depend on the annealing treatments designed to change the oxygen concentration. A qualitative explanation is presented within the framework of antiferromagnetic phase transition (δ ≥ 0.6) and martensite-like transformation related to a rearrangement of oxygen atoms.

Heat capacity measurements of hafnium-oxygen solid solutions at high temperatures

Heat capacities of hafnium-oxygen alloys, HfO X ( X = 0.14, 0.17 and 0.19), were measured from 325 to 905 K by using an adiabatic scanning calorimeter. A λ type heat capacity anomaly was observed around 700 K for all the samples, and was assigned to an order-disorder rearrangement of oxygen atoms. The measured values for the entropies of the order-disorder transition are in good agreement with the theoretical values in the composition range of X ≤ 1 6 ( X = 0.14 and 0.17), but smaller than the theoretical value in the range of X > 1 6 (X = 0.19) . Another heat capacity anomaly was observed at a temperature lower than that of the order-disorder transition for the well-annealed samples. The appearance of this anomaly depends on the annealing conditions of the samples.

Enhancement of T c in argon-pretreated NdSrBaCu3O6+z

NdSrBaCu3O6+z prepared in air followed by oxygen annealing showed a Tc of 68 K. The Tc of the sample when treated in argon followed by oxygen annealing increased by 10 K. This could be related to the observed shrinking of the c axis and/or a rearrangement of oxygen atoms in the basal plane.

Heat-capacity measurement on ( Zr1− ySny) Ox from 325 to 905 K

Heat capacities of ( Zr 1− y Sn y ) O 0.17 and ( Zr 1− y Sn y ) O 0.28 ( y = 0−0.07) having α''-ZrO ~ 1 6 and α''- ZrO x type crystal structures, respectively, were measured from 325 to 905 K by using an adiabatic scanning calorimeter. Two kinds of heat capacity anomalies were observed for all samples. The anomaly at lower temperatures is attributed to a nonequilibrium phenomenon. Another anomaly at higher temperatures is assigned to an order-disorder rearrangement of oxygen atoms. The transition temperature, transition enthalpy and entropy changes due to the order-disorder transition decreased with increasing tin content, indicating that arrangement of oxygen atoms in the lower temperature phase may be partially disordered by substituting tin for zirconium. The entropy change due to the order-disorder transition for ( Zr 1− y Sn y ) O 0.17 and ( Zr 1− y Sn y ) O 0.28 solid solutions is compared with the theoretical value. The solubility limits of ( Zr 1− y Sn y ) O 0.17 and ( Zr 1− y Sn y ) O 0.28 were determined from the variation of lattice constants, transition temperature, transition enthalpy and entropy changes against tin content.

Heat capacity measurement of ZrOx and (Zr1−yNby)Ox from 325 TO 905 K

Heat capacities of zirconium-oxygen alloys, ZrOx (x=0.17, 0.20, 0.28 and 0.31), and those of niobium doped alloys, (Zr1−yNby)Ox (x=0.17 and 0.28, y=0.005 and 0.01), were measured from 325 to 905 K by an adiabatic scanning calorimeter. Two kinds of heat capacity anomalies were observed for all samples. The anomaly at higher temperatures was assigned to be due to an order-disorder rearrangement of oxygen atoms. Another anomaly at lower temperatures was due to a non-equilibrium phenomenon. The entropy change due to the order-disorder transition for Zr-O solid solution at higher temperature obtained from this experiment was compared with the theoretical value. The transition temperature, transition enthalpy and entropy changes due to the order-disorder transition decreased with increasing niobium contents, indicating that arrangement of oxygen atoms in lower temperature phase may be partially disordered by the interaction between niobium and oxygen atoms.

Monoenergetic Positron Beam Studies of Oxygen in Single Crystal Silicon - Stress Induced Clustering of Oxygen Atoms in Silicon

ABSTRACTA monoenergetic positron beam has been used to investigate the state of interstitial oxygen in Czochralski (CZ)-grown Si with either thermally grown S1O2 (100 nm thick) or silicon oxide (p-SiOx) deposited by plasma enhanced chemical vaper deposition technique on the surface. Both the growth of thermal SiO2 and the deposition of SiOx film resulted in a reduction of the doppler-broadening line shape parameter (S-parameter) for the positron annihilation in the bulk silicon region. Annealing at 450δC, the removal of oxide overlayer or long-term aging at room temperature caused the S-parameter to return to its intrinsic value. It was thought that tensile stress in silicon, induced by the thermal oxidation or the deposition of SiOx films which had compressive internal stress themselves, enhanced the rearrangement of oxygen atoms and caused the formation of oxygen clusters in silicon crystal. Oxygen interstitial clusters can trap positrons leading to the lower S-parameter value for annihilation in the bulk silicon region, because of large overlap with core electrons. The above results suggest that oxygen atoms can absorb lattice strain by clustering and thus prevent the generation of dislocations against external stress in the Si lattice. This results yield an additional explanation of the high mechanical strength of CZ Si crystal.

Stress-induced rearrangement of oxygen atoms in Si investigated by a monoenergetic positron beam

A monoenergetic positron beam has been used to investigate the state of interstitial oxygen in Czochralski-grown Si with coverage of SiO2 (100 nm) and poly-Si (200 nm)/SiO2 (100 nm), respectively. It was found that (i) the growth of SiO2 gives rise to a strong Doppler broadening of positrons in the bulk of Si and (ii) such a broadening can be recovered to the original level by annealing at 450 °C, by the removal of overlayers using chemical etching and by long-term aging at room temperature. This broadening was assigned to arise from the positron trapping by oxygen interstitial clusters. It was concluded that film stress is responsible for the rearrangement of oxygen atoms in Czochralski-grown Si.