Numerical simulation of C/C/C planar X-ray waveguides.

A numerical simulation was done to check the possibility of using planar C/C/C multilayers with density contrast 0.2 and 0.7 g/cm3 as an X-ray waveguide. After an optimization procedure, suitable waveguide layer thicknesses were found which provide a high degree of resonant standing wave field intensity enhancement in the core layer at incident beam energy of 13 keV. The obtained results were compared with those of the Mo/Be/Mo waveguide, whose high waveguiding capability at the same energy value was reported in the 1990s. The comparison shows that standing wave field intensity resonant enhancement provided by C/C/C planar multilayers is very high and, consequently, a guided beam can be well detected.     

Murahashi Cross-Coupling at −78 °C: A One-Pot Procedure for Sequential C−C/C−C,C−C/C−N,and C−C/C−S Cross-Coupling of Bromo-Chloro-Arenes

The coupling of organolithium reagents, including strongly hindered examples, at cryogenic temperatures (as low as −78 °C) has been achieved with high-reactivity Pd-NHC catalysts. A temperature-dependent chemoselectivity trigger has been developed for the selective coupling of aryl bromides in the presence of chlorides. Building on this, a one-pot, sequential coupling strategy is presented for the rapid construction of advanced building blocks. Importantly, one-shot addition of alkyllithium compounds to Pd cross-coupling reactions has been achieved, eliminating the need for slow addition by syringe pump.     

Highly efficient Fe/N/C catalyst using adenosine as C/N-source for APEFC

An environmentally friendly precursor, adenosine, has been used as a dual source of C and N to synthesize nitrogen-doped carbon catalyst with/without Fe. A hydrothermal carbonization method has been used and water is the carbonization media. The morphology of samples with/without Fe component has been compared by HRTEM, and the result shows that Fe can promote the graphitization of carbon. Further electro-chemical test shows that the oxygen reduction reaction(ORR) catalytic activity of Fe-containing sample(C–Fe N) is much higher than that of the Fe-free sample(C–N). Additionally, the intermediates of C–Fe N formed during each synthetic procedure have been thoroughly characterized by multiple methods,and the function of each procedure has been discussed. The C–Fe N sample exhibits high electro-catalytic stability and superior electro-catalytic activity toward ORR in alkaline media, with its half-wave potential 20 mV lower than that of commercial Pt/C(40 wt%). It is further incorporated into alkaline polymer electrolyte fuel cell(APEFC) as the cathode material and led to a power density of 100 m W/cm~2.     

C/C composite anodes for long-life lithium-ion batteries

The research of anodic materials which could improve the performance and reduce the cost of graphite-based materials in lithium-ion batteries leads to a considerable effort for creating novel carbons. In this work, special attention has been paid to investigating the possibility of improving the electrochemical behavior of graphite anode by application of composite materials with carbon materials coming from agro-wastes. For that, different carbons coming from agro-wastes have been synthesized and characterized in order to study the effect of their properties on the electrochemical performance of C/C composites with graphite. It has been established that introduction of hard carbon obtained from olive stones into the active mass of anode based on graphite allows one to increase the reversible capacity up to 405 mAh g^?1 for the total mass of graphite/carbon content of electrode, and also to improve stability of characteristics during cycling. We suggested that such a binary carbon mixture (graphite and hard carbon) would be a better choice for development of the anode for lithium-ion battery.     

甲醇在Pt/C和Pt/WO3/C电极上的电氧化

用液相还原法制备碳载Pt(Pt/C)和碳载Pt/WO3(Pt/WO3/C)催化剂.实验表明该催化剂中加入一定量的WO3后,其对甲醇的催化氧化活性和稳定性都有一定提高,并以Pt、W原子比为1∶1的催化剂性能最好.这是由于Pt催化剂中加入了WO3后,其电化学活性比表面积增大,并且降低了对CO吸附强度.     

Synthesis of Mo2C/MoC/C nanocomposite for hydrogen evolution reaction

Journal of Solid State Electrochemistry - Our energy sources such as fossil fuels and coal are limited and cause air pollution. Hydrogen has been promoted as an alternative source of energy, which...     

Direct borohydride oxidation electrocatalysts based on Ni-Ru/C and Ni-Ru-F/C alloys

A fluorine-containing bimetallic nickel-ruthenium catalyst on highly disperse carbon black is synthesized based on an organometal nickel complex and a ruthenium cluster in the presence of perfluoroenanthic acid. The resulting catalyst is characterized by the XRD and energy-dispersion analyses and laser mass spectrometry. The overall composition of the catalytic system corresponds to Ni₁₂RuF₅. Calculated on the base of XRD data, the particle size is 10.5–12 nm. According to voltammetric data, the specific characteristics of the synthesized catalyst in the reaction of direct oxidation of sodium borohydride at room temperature surpass the characteristics of nickel-ruthenium catalyst described in the literature.     

Submicro-sized porous SiO2/C and SiO2/C/graphene spheres for lithium ion batteries

Journal of Solid State Electrochemistry - In order to improve electrochemical performance of inert SiO2 anode for lithium ion batteries, submicro-sized porous SiO2/C and SiO2/C/graphene spheres...     

Electrochemical study of PtRh/C and PtRhNi/C electrocatalysts for ethylene glycol oxidation

Journal of Solid State Electrochemistry - In the last decades, the ethylene glycol has been considered as another option of fuel, in both acid and alkaline solutions, for fuel cells application....     

C_(60)/C_(70)及其衍生物(C_(60)Cl_n/C_(70)Cl_n)在丁二烯阴离子聚合中的偶联作用

Fullerene(富勒烯)独特的结构和性质吸引了高分子界广泛的关注.迄今,已通过和自由基共聚[1]、活性自由基聚合[2]、阳离子聚合[3]、阴离子聚合[4～8]以及配位聚合[9～13]等诸多方法相结合制备出了种类繁多的富勒烯高分子衍生物.不仅如此,富勒烯家族的重要分支--富勒烯卤化物,其独特的分子结构和具有的新性质也甚引起人们的重视[14,15].     

Mechanical properties and fracture behaviors of C/C composites with PyC/TaC/PyC,PyC/SiC/TaC/PyC multi-interlayers

Carbon/carbon (C/C) composites with PyC/TaC/PyC or PyC/SiC/TaC/PyC multi-interlayers were prepared by isothermal chemical vapor infiltration, followed by Furan resin impregnation and carbonization. Microstructures, mechanical properties including flexural strength, ductile displacement, and fracture behaviors of composites were studied. Furthermore, composites were heat treated at 2000 °C to study the effects of heat treatment on mechanical properties and fracture behaviors. PyC/TaC/PyC and PyC/SiC/TaC/PyC multi-interlayers have been deposited uniformly in C/C composites. With the introduction of PyC/TaC/PyC multi-interlayers in C/C composites, the flexural strength decreases; however, the ductile displacement increases. The fracture behavior changes from brittleness (0% TaC) to pseudo-ductility (5% TaC) and high toughness (10% TaC). When PyC/SiC/TaC/PyC multi-interlayers are introduced in C/C composites, the flexural strength is improved remarkably from 270 MPa to 522 MPa, but the ductile displacement decreases obviously from 0.49 mm to 0.24 mm, and the fracture behavior becomes brittle again. After heat treatment at 2000 °C, the flexural strength decreases, but the ductile displacement increases and pseudo-ductility or high toughness can be obtained.     

Methane activation at low temperature in an acidic electrolyte using PdAu/C,PdCu/C,and PdTiO2/C electrocatalysts for PEMFC

Pd/C, PdAu/C, PdCu/C, and PdTiO₂/C electrocatalysts were prepared by a sodium borohydride reduction process for methane activation at low temperatures in a PEMFC reactor. These electrocatalysts were characterized by XRD, TEM, XPS, ICP-MS, ATR-FTIR, and cyclic voltammetry. The diffractograms of Pd/C, PdAu(50:50)/C, PdCu(50:50)/C, and PdTiO₂(50:50)/C electrocatalysts showed peaks associated with Pd face-centered cubic structure. PdAu(50:50)/C showed a small shift in the peak center when it was compared to Pd/C, while PdCu(50:50)/C showed a shift to higher angles when it was also compared to Pd/C. This effect can be due to the formation of an alloy between Pd and Au, and Pd and Cu. By TEM experiments, a mean nanoparticle size was observed between 6.9 and 8.9 nm for all electrocatalysts. Cyclic voltammograms of Pd/C, PdAu/C, PdCu/C and PdTiO₂/C electrocatalysts showed an increase in current density values after the adsorption of methane The ATR-FTIR experiments showed for all electrocatalysts the formation of methanol and formic acidic. Polarization curves at 80 °C acquired in a PEMFC reactor showed that PdAu(50:50)/C and PdTiO₂(50:50)/C had superior performance when compared to Pd/C, indicating the beneficial effect of adding the co-catalyst; this behavior has been attributed to the bifunctional mechanism or electronic effect.

     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

Kinetic study of liquid-phase hydrodechlorination of hexachlorobenzene on Ni/C and 2%PdNi/C

Liquid-phase hydrodechlorination of hexachlorobenzene was kinetically studied in the presence of both nickel (Ni/C) and palladium-promoted nickel (2%PdNi/C) catalysts under different reaction conditions. Molecular hydrogen (at 1 and 20 atm) and sodium borohydride (NaBH₄) were used as reducing agents. In the presence of the nickel catalyst, the hydrodechlorination of C₆Cl₆ occurs via a consecutive mechanism (removal of one chlorine atom from the substrate at each stage), whereas with the 2%PdNi/C catalyst, the transformation of C₆Cl₆ occurs via both consecutive and multiplet mechanism (with the elimination of several chlorine atoms without desorption of the chloroaromatic substrate from the catalyst surface). The promotion of the nickel catalysts with palladium substantially changes the selectivity of formation of intermediate products of C₆C1₆ dechlorination. The mechanism of hydrodechlorination of hexachlorobenzene was suggested that explained the presence of only certain products of partial dechlorination of hexachlorobenzene in the reaction medium.     

C1 Oxidation/C2 Reduction Isomerization of Unprotected Aldoses Induced by Light/Ketone

Unprotected aldoses in water undergo an isomerization reaction via a radical pathway when irradiated with light in the presence of water‐soluble benzophenone. Whereas its anomeric carbon (C1) is oxidized to a carboxy group, the hydroxy group on the C2 carbon is replaced by hydrogen. The generated 2‐deoxy lactones are readily reduced to the corresponding 2‐deoxy aldoses, which are often contained in bioactive compounds.     

Oxidation of 1,3-butadiene over Pd/C and Pd-Te/C catalysts in polar media

The oxidation of 1,3-butadiene over the Pd/C and Pd-Te/C heterogeneous catalysts occurs in organic solvents containing water at a temperature of 100°C and an oxygen partial pressure of $P_{\left[ {O_2 } \right]} = 4$ atm. Crotonaldehyde dominates among the three major products of oxidation over the Pd catalyst. The introduction of Te into the catalyst increases the methyl vinyl ketone yield, the furan yield being the lowest in all cases. X-ray photoelectron spectroscopy (XPS) showed that the active catalyst components can be in a partially oxidized state, particularly after storing the catalysts in air. Additional hydrogen treatment results in almost complete reduction of the active components to metals and enhances the catalytic activity. It is supposed that the oxidation of 1,3-butadiene over the Pd-Te catalysts proceeds via the activation of dioxygen over the Pd⁰ sites, with oxidized Pd and Te participating in subsequent chemical transformations.